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ISO 8583 Tutorial – Introduction for Beginners

noreply@blogger.com (Hamid) — Wed, 26 Feb 2014 10:31:00 +0530

Introduction

reference Jimmy Blog
All (or most?) financial transaction is using ISO 8583 standard, which at first I thought is a complicated standard. But after learn and see how it implemented it’s not as complex as I thought.
In this post I will try to explain (based on my experience before I go deeper on the programming side.
Although it’s a ’standard’ I see that’s many variant for the detail implementation of ISO 8583.
Financial transaction is communication between 2 system through socket connection.
After connection established, each system can send message in ISO 8583 format which commonly will be request and the other system will response.
From my experience the communication will be start with sign on and then the financial transactions.
Periodically an echo message is send to make sure the other system is still alive.
If I break down the flow:

System A open connection to System B (through specific IP and Port).
Connection established.
System A send Sign-On request message.
System B send Sign-on response message.
System A will start send Echo request message periodically (e.g every 1 minute).
System B will send Echo response message when receive Echo request message.
When financial transaction happen, System A will send Transaction request message.
Then System B will send Transaction response message.
If something wrong happen (usually timeout so System A didn’t get the response), System A will send Reversal request message to cancel the previous transaction.
System B will send Reversal response message.

I hope my explaination give clear basic understanding about the flow.
Next the question will be what’s this ISO 8583 message looks like.
We can separate the message into 3 parts:

Message Type Identifier
Bitmaps
Data Elements

ISO8583 – structure

Message Type Identifier

Message Type Identifier or MTI is 4 digits numeric that describe the message type. It will explain the message function.
Commonly used:
- 02xx : Financial Message (e.g 0200 for request, 0210 for response)
- 04xx : Reversal Message (e.g 0400 for request, 0410 for response)
- 08xx : Network Management Message (e.g 0800 for request, 0810 for response)
* I found more detail & complete list at wikipedia

Bitmaps

Bitmaps is field that contain information about which data element is presence or absence. Based on the variant it could be 16 hexadecimal characters.
An example will make it clear.
The bitmap is:
B220000000100000
If we break down to binary (I hope you understand how to convert hexadecimal to binary:) :
1011001000100000000000000000000000000000000100000000000000000000
Since I’m nice I create graphical illustration.

Bitmap sample
You can see that in this bitmap it explain that data element in the message is 1, 3, 4, 7, 11.
There’s special meaning of first bit of bitmap, if it has value of 1 that mean there’s secondary bitmap.
And what the hell is this secondary bitmap?
Since 16 hexadecimal characters will can only contain info of 64 data element, some transactions contain data element number 64 – 128. That mean the 16 hexadecimal characters is not sufficient.
With set the first bit to ‘1′ that will inform there’s additional bitmap, which is another 16 hexadecimal characters.
So in this case the full bitmap example should be:
B2200000001000000000000000800000
Convert to binary:
10110010001000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000100000000000000000000000
From the bitmap, data element presence in the message : 3, 4, 7, 11, 105.

Sample Bitmap complete

Data Elements

Data Elements is the essense of the whole ISO message, contain information about the transaction (transaction type, amount, customer id, etc).
Each data element have their on format, attribute and length.
Each data element number also have standard purpose, for example DE #4 is transaction amount.
I will explain based on the example above, since this is only introduction I don’t want to confuse beginner reader. In wikipedia there’s full list.
For our examples, the data element list:

#3 – Processing code – n 6
#4 – Transaction amount – n 12
#7 – Transmission date & time – n 10
#11 – Systems trace audit number – n 6
#44 – Additional response data – an ..25
#105 – Reserved for ISO use – ans …999

To make it practical let’s just use example.
We want to send :

DE #3 : 201234
DE #4 : 10000
DE #7 : 1107221830
DE #11 : 123456
DE #44 : A5DFGR
DE #105 : ABCDEFGHIJ 1234567890

Using above value, the data in data elements :

ISO8583 – de
Based on the type each value will be formatted.

a : alpha (including blanks)
n : numeric value
s : special characters
x (no dot) : length is x (fixed)
.x (one dot) : max length is x (1 digit in front as length info)
..xx (two dot) : max length is xx (2 digit in front as length info)
…xxx (three dot) : max length is xxx (3 digit in front as length info)

ISO Message

From above examples the whole ISO message will be :
0200B2200000001000000000000000800000201234000000010000110722183012345606A5DFGR021ABCDEFGHIJ 1234567890

Conclusion

Ok. This article already long enough
Actually I always prefer short article, but on this case it’s cannot be to short.
Anyway, I hope this article is clear enough for you.
Like always, just drop question in the comment if you confused.

How to Get More Facebook Likes for Your Page

noreply@blogger.com (Hamid) — Sun, 3 Nov 2013 20:02:00 +0530

10 Easy Ways to Get More Facebook Likes for Your Business Page

In order to achieve success on Facebook you need a community. That’s a fact. If you don’t have a community, you don’t have anyone listening to you, and if there’s no one listening to you, it’s difficult to build brand awareness and deliver ROI.
You need a community filled with people who like you and share your content with like-minded friends. But it’s not just about the quantity of Facebook likes that you collect, it’s about the quality; attracting Facebook likes from a group targeted to suit your business goals whose comments (and endorsement!) can increase your shares on Facebook.
So here are ten quick and easy tips to drive targeted Facebook likes to your business page.

1. Complete your Facebook Page Profile

Your Facebook Page is the first thing people see when they come to visit you on Facebook. Let visitors know why they should like you! Create a catchy description and make sure you categorize your page correctly. Also make sure to list your address, phone number and hours of operation (if applicable). Not only will this inform your potential followers, it will tell Facebook what kind of organization you are you so they know to show your page when users are searching for companies like yours – which can increase your Facebook likes even more!

2. Ask friends and other contacts to like you on Facebook

Friends are like underpants. Some snap under pressure, some are a little twisted, but some will give you support. When you first create a Facebook Page like this PAGE invite your supportive friends, family and business partners to like your Facebook Page. These initial likes will give you higher social media credibility and visibility. Then, alert your customers, prospects and your other social communities, and promote your Facebook page anywhere you mention your website. If people don’t know your Facebook page exists, they can’t like it.

3. Add social plugins to your website

Visitors on your website should be able to find your Facebook Page easily. My recommendation is to use Facebook’s Social Plugins, like the Like box plugin, to get more Facebook likes. These plugins include a like button, your recent posts, and pictures of some of your fans.

4. Find out what interests your community

With Facebook’s new Graph Search it’s really easy to find out what interests your target community, and post relevant content to increase Facebook likes.
Here’s a real example:
I have a Facebook Page Shocking fb Tircks on facebook . To learn more about my target community’s interests, I search for “how many people like facebook trick".

This information is great to have at hand when I’m thinking about what to post on my Facebook page. By posting content that my audience is interested in (for example, suggesting how to secure your password and all) they will share it with their friends and help me get more Facebook likes. This same content will also attract likes from people who come to my Facebook page from my website, email signature, or a Facebook search.

5. Use Facebook Ads

Facebook ads are another great way to increase Facebook likes. To get the most out of your ads, you can target by your community’s interests to find people similar to your current fans.
In the image below, you can see how I’ve used the information that I got from Graph Search and how I’ve targeted my ad for my new pizza place.

Experiment with different types of ads to see what works best for your organization, and make sure you choose the option that allows Facebook users to like your page directly from the ad.

6. Run a contest

There are many companies that have created successful contests on Facebook that resulted in many thousands of Facebook likes. But there are some things that you need to know before you create your own contest. For starters, make sure that your contest follows Facebook’s promotion guidelines. Your contest must use a Facebook app, which allows you to create a fan-gate, so that only those who first like your page can participate in the contest. Apps also have a unique URL, so you can promote your contest with a Facebook ad and increase Facebook likes even more.
Also, when you create a contest make sure that your app is working for mobile users, that the content of the contest is funny, that it’s easy to participate and that the contest encourage users to share their result and participation with their friends.

7. Like, and interact with, other companies

Did you know that you can engage with other company pages as your Business Page on Facebook? This is a great way to build awareness among like-minded companies and their followers. To do this, visit your Facebook Page, click on “Edit Page” in your Admin Panel and select “Use Facebook as YourPage.”

Finding companies to like and interact with is easy. Use Graph search and search for e.g. companies, pages, places that is of interests for your company and like these Pages (you can’t like personal profiles).

After you have liked some Pages, you can view your company’s Newsfeed and engage with the pages you like. Not only is the company likely to follow you back, but their engagement with your page will help you increase Facebook likes amongst their followers as well.

8. Publish engaging content

It’s important to publish engaging, entertaining and interesting posts on a regular basis, and to keep an eye out for the posts that get the most engagement. If your posts are valuable to your followers, then they will share your posts with their friends, helping you increase your Facebook likes. Images are among the best types of post for driving engagement so make sure you publish images your followers can relate to and will like. You may also want to include calls to action in some of your posts, asking followers to like, comment or share your content, or ask your community a question.

9. Be active

By now you know that you should publish engaging, interesting and entertaining content. But how often should you post? There is no magic number but there are best practices and analytics to guide you. Post at least one status update per day, and experiment with the timing of your posts to see when the majority of your followers are active. People are unlikely to like your Facebook page if you don’t post regularly – and they certainly won’t engage with your content (or help you get more likes) if they don’t see your posts.

10. Measure, analyze and learn

Use Facebook Insights to find useful metrics on your page performance. You can see things like reach (how many users are seeing your posts), engaged users (how many users engage with your posts) and new likes (when and why do you get new followers). These metrics will help you understand what’s driving your likes and engagement, so that you can adjust your posts accordingly. If you would like to know if you have good engagement, or want other recommendations for improvement, try out our free Facebook analytics tool, LikeAlyzer.

Now you people think what about my own Website page, let me tell you I have more than 20 pages some of them have more than 2 lacs users and I am the only person who handles this.
check this out AASHIQUI2.
Would you like to add any tips for getting more Facebook likes? Did I forget something? Please add a comment and, if you like the post, feel free to share it with your friends.
Click Here To Know More

Introducing Next browser for Android, Experience the NextGen browsing

noreply@blogger.com (Hamid) — Sun, 3 Nov 2013 19:28:00 +0530

Next-Generation browser for Android-NEXT BROWSER

Android is the most advance operating system for mobile and it makes a smartphone even smarter. So, why not use the most advance web browser for the smart operating system. We are talking about the Next Browser for Android. This Next Browser is developed by Go Dev Team who are the developers of the most widely used Go Launchers set of themes.
It is far ahead from other browsers because it provides you with everything that you need while surfing in a browser such as, Flash player, Java and even a wide range of extensions that very few browser supports like Dolphin Browser and Firefox for Android. We will provide the list of extensions below.
Every other browser has it’s own feature such as Chrome has multi-tab browsing, Firefox offers extensions and Opera Mini is powered with lightning fast speed. But, what Go Launcher team has done is, they have taken the best features of all the above mentioned browsers and came up with a new, Next Browser. It has the option of multi-task, most visited site page, RSS view of your favorite sites, large pack of extensions and other cool features.

Here are some major Extensions in the Next Browser:
And many other extensions available. You can view the extensions by swiping to the left from the edge of the screen. It also supports Flash and has the options to disable Flash, enable Flash or enable when required.
The best part of this app is that it is free of cost and it can be downloaded from the Play Store.
Download:>> Next Browser

Android KitKat (4.4) is going to expand Google marketshare

noreply@blogger.com (Hamid) — Sat, 2 Nov 2013 12:48:00 +0530

SAN FRANCISCO: Google on Thursday unveiled the newest version of its Android smartphone software, aiming to allow more smartphone users access to its evolving menu of online services such as driving directions voice-activated search.

The new "KitKat" version of Android will be able to run on inexpensive, low-end smartphones as well as the most advanced devices, Sundar Pichai, Google senior vice president of Android, Chrome and Apps said at a press event in San Francisco.

"Now you have one version of the operating system which will run across all versions of Android smartphones," Pichai said, noting that smartphones sold in "emerging markets" often come loaded with older versions of Android, that lack many key features and capabilities.

The move could help Google ensure that more users have access to the growing selection of profitable online services. It also could make the Android software more attractive to third-party app developers, who have been frustrated by what they call the "fragmented" nature of Android devices.

Google's Android software runs on 80% of the world's smartphones, according to industry analysts. But many of the Android devices sold use older versions of the software, which are not compatible with many new features.

Many developers still build apps intended for Apple's iPhone and iPad first, said BGC Partners analyst Colin Gillis.

"You want your users to be using your services, and KitKat will help foster that," said Gillis.

Roughly 29% of the Android smartphones in operation as of Oct. 2 feature the " Gingerbread" version of the operating system. Introduced in December 2010, that version of Android relies on an older Web browser and does not support Google Now, a sort of personal digital assistant technology that automatically provides relevant information about a user's personal calendar, weather and travel plans.

The new KitKat version of Android integrates Google search technology directly into the phone in various ways. The phone's contact list allows users to find phone numbers of their personal acquaintances as well as of local businesses, such as restaurants and dry cleaners.

Google also showed off a new feature that will allow smartphone users to find information by searching pages on the Web as well as information within the apps they have loaded on their phones. A search for a particular chocolate cookie recipe, for example, could yield results from a cooking app.

Google also showed off the new Nexus 5 smartphone which will be the first device to feature the KitKat software. The phone, built by LG, will be available in 10 countries starting Thursday without a contract for $349.

Barack Obama's Twitter, Facebook, Campaign website and Email Accounts hacked by Syrian Electronic Army

noreply@blogger.com (Hamid) — Sat, 2 Nov 2013 12:41:00 +0530

The pro-Assad group Syrian Electronic Army claims it has hacked the President Barack Obama’s website , Twitter-Facebook accounts and access email accounts linked to Organizing For Action, the non-profit offshoot of Obama For America, Obama's 2012 campaign operation.

Last night, Syrian Electronic Army (SEA) hacked into Obama's donation website donate.barackobama.com, which was temporarily redirected to the website of the hacking group (sea.sy/indexs/) with a short message: “Hacked by SEA”.

The hackers were able to take over only a secondary donations page. It was an older page - still on the site, but was no longer being used.

They have also posted fake tweets and updates from Obama's Facebook Page and Twitter accounts, "All the links that Barack Obama account tweeted it and post it on Facebook was redirected to a video showing the truth about Syria" Hacker told Mashable in an interview.

The attackers also compromised the URL shortening service that the President used to share links through social media (ShortSwitch.com). The compromised links directed users to a video called “Syria Facing Terrorism”, hosted on YouTube, which has since been removed.

At the time of writing, the donate.barackobama.com website no longer redirects visitors to the SEA’s website, but the links posted on his Twitter and Facebook accounts had not been fixed as of publishing time.

According to a screenshot shared by the hacking group, they have also claimed that they have access Obama Campaign email accounts.

Zone-H mirrors of hack are also available for readers:

Link 1 (http://donate.barackobama.com)
Link 2 (https://my.barackobama.com/page/s/hacked-by-sea)

'Syrian Electronic Army is an organized hacking group loyal to the Syrian President Bashar al-Assad and known for their high profile cyber attacks. This year they were able to disrupt the New York Times web page multiple times, Twitter, CNN, the Huffington Post and Global Post and many more targets.

The SEA website launched in May 2011 stating the group's mission: to attack the enemies of the Syrian government, mainly those who fabricated stories about the Syrian civil war.

Hacked Facebook Account with One SMS.

noreply@blogger.com (Hamid) — Wed, 30 Oct 2013 18:09:00 +0530

Hacked Facebook Account with One SMS by UK based Hacker, Facebook Security Team rewarded him reporting flaws in the System.

Guys Today's story is different from others. People usually use Malicious code, Social Engineering, Trojans, Phishing to Hack a Facebook Account, But this story is entirely change, here Hacker called "fin1te" which is from UK found a big flaws in Facebook messaging system, reported to Facebook and Facebook rewarded him By $20,000 US.

Today I am going to explain you that how a UK based Security Researcher, "fin1te" is able to hack any Facebook account within a minute by doing one SMS.

Because 90% of us are Facebook user too, so we know that there is an option of linking your mobile number with your account, which allows you to receive Facebook account updates via SMS directly to your mobile and also you can login into your account using that linked number rather than your email address or username.

According to hacker, the loophole was in phone number linking process, or in technical terms, at file /ajax/settings/mobile/confirm_phone.php

This particular webpage works in background when user submit his phone number and verification code, sent by Facebook to mobile. That submission form having two main parameters, one for verification code, and second is profile_id, which is the account to link the number to.

As attacker, follow these steps to execute hack:

Change value of profile_id to the Victim's profile_id value by tampering the parameters.

Send the letter F to 32665, which is Facebook’s SMS shortcode in the UK. You will receive an 8 character verification code back.
Enter that code in the box or as confirmation_code parameter value and Submit the form.

Facebook will accept that confirmation code and attacker's mobile number will be linked to victim's Facebook profile.

In next step hacker just need to go to Forgot password option and initiate the password reset request against of victim's account.

Attacker now can get password recovery code to his own mobile number which is linked to victim's account using above steps. Enter the code and Reset the password!

Facebook no longer accepting the profile_id parameter from the user end after receiving the bug report from the hacker.

In return, Facebook paying $20,000 to fin1te as Bug Bounty.

Found Really interesting??
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10 Simple Tips to Secure Your Email Account

noreply@blogger.com (Hamid) — Mon, 28 Oct 2013 20:02:00 +0530

10 Simple Tips to Secure Your Email Account:

It’s tough to get people to pay attention and be serious about their online identity. An Email account is the first and primary component of your online identity and yet it’s the one that is left unguarded the most. Email accounts may be virtual but once hacked, the consequences and damages are very real.
The problem with a hacked email account is the domino effect. All registrations, purchases, renewals, transactions, password reminders etc. are sent to your email inbox. So once the first domino falls, the entire setup falls apart in one fell swoop. After the jump, we’ve rounded up a few tips that can help you secure your email accounts of popular webmail services.

Use a Strong Password

Strong Password

Yes, I know this is what every other tech blogger says every single time. But that has never made people any wiser. Even hackers feel insulted when they come across passwords like “sweetlove123”, “pass@123” and the like. Google is the best when it comes to putting real effort into securing your email account proactively. You can use special characters, numbers, upper and lower case alphabets of almost any length. My Gmail password is between 60 to 80 characters long and my general rule of thumb is to have a password that only the NSA can hack.

Use a reliable Secondary Email Address

Absolutely no Hotmail accounts for secondary fallback email account people. They still have their stone age era email account expiry plan after certain number days of non usage. So if the secondary email address is Hotmail and is expired, anyone create it back again to receive password reset information. And since webmail providers have this peculiar habit of giving all kinds of hints to remind you of the email address where the password recovery link has been sent, use an uncommon, custom domain or corporate email address that is hard to guess and hack into.

Setup SMS Alerts

SMS Alerts

Go to your account settings and add your mobile number to receive SMS alerts. Once that’s set up, Google will send you the password reset code whenever somebody tries to reset your password. Alternatively, if you are a smartphone user, you can rely on these SMS alerts and disable password recovery via email altogether. Email accounts are always vulnerable to a hacker from a remote place but your mobile phone is not. Yahoo provides the same feature free too. Hotmail has a similar feature but is not supported in a lot of countries.

Be sensible with your security question

Ok. There’s absolutely no point in having the security question, “My favorite doggy”, and posting pics of you and your poodle with images titled “Rolling with Rosy” on Facebook and Twitter. A lot of personal information is available online, thanks to social networks. On being the weakest links in the email security chain, security questions rank ahead of weak passwords. It’s nice to be an open book but select a question from those stapled pages and blacked out lines.

Check Filters and Forwarding Addresses

In the event of a hack and after reclaiming the account, go through the existing filters to check if there are some sneaky filters set up that forward all your credit card, login info, bank account and other sensitive correspondence to an email address that is not yours. Go to the forwarding page and see that all your incoming mails are not forwarded to the hacker either. This helps you avoid getting hacked in the future too.

Avoid Public WiFi

Happy to have discovered an unsecured WiFi hotspot? Or mooching your neighbour’s spilt WiFi? Enjoying the free WiFi of the coffee shop round the corner? Good for you and so is for the hacker sitting nearby to sniff the packets right out of thin air. Avoid using public WiFi for accessing email or transacting online with a credit card. Casual browsing and YouTube watching (without logging in) are Ok. Accessing emails is a big no, no.

Do not share your login information

Another obvious fact. But at times, it’s necessary for small businesses and online entrepreneurs to share login information with colleagues. For example, accessing Google AdSense, Analytics or Microsoft Live services etc. The ideal solution is to create a dedicated account for accessing these services instead of linking everything to your personal email id and sharing it.

Login regularly

Even if a hacker gets hold of the answer to your security question, they cannot use it immediately to reset the password and break into your Gmail account. Password reset with security question is possible only after 24 hours of your account being inactive after receiving the password reset instructions. So for once, checking your mail regularly is a good thing. Also, it will help reset the Hotmail account’s expiry date. Unfortunately Hotmail and Yahoo do not have this useful restriction in place.

Special Features

Gmail

Enable HTTPS by default from your account settings. This helps from the password getting sniffed when transmitted over public WiFi hot spots. If you are a Google Apps user, enable pre release features to avail the upcoming two factor authentication system before it launches.

Hotmail

Use the Windows Live Essentials package and verify the computer you are using as reliable. “Trusted PC” is a unique new proof that lets you link your Hotmail account with one or more of your personal computers. Then, if you ever need to regain control of your account by resetting your password, you simply have to use the trusted computer and Hotmail will know you are the legitimate owner. It’s a great feature for those who are really paranoid about email security.

Yahoo

Make use of the sign in seal option to verify the computer. Sign in seal is basically an image or color that Yahoo displays for each of your computers adding another layer of security to the login process.

Avoid Webmail

Still not sure about the safety and security of your email account online? It is totally understandable and I suggest you to take it off the Internet. I mean, partially. Get hold of an ISP and get a POP or IMAP account set up for your email address forgoing the webmail set up. Then use desktop email clients like Outlook or Thunderbird to pull your mails. It will make you feel dated, but is reliable and works effectively too.
Did we miss an important tip or got a better suggestion? Share it with the rest of community in the comments section.

Mobile device could be dangerous for You

noreply@blogger.com (Hamid) — Tue, 22 Oct 2013 19:25:00 +0530

READ THIS!!!!

IMPORTANT FROM THE UNIVERSITY OF MIAMI HOSPITAL

VERY SERIOUS WARNING...

I do this all the time! I guess I won't be doing it ANY more !

A few days ago, a person was recharging his mobile phone at home.

Just at that time a call came in and he answered it with the charging Instrument still connected to the outlet.

After a few seconds electricity flowed into the cell phone unrestrained and the young man was thrown to the floor with a heavy thud. As you can see, the phone actually exploded.

His parents rushed to the room only to find him unconscious, with a weak heartbeat and burnt fingers.

He was rushed to the nearby hospital, but was pronounced dead on arrival.

Cell phones are a very useful modern invention.

However, we must be aware that it can also be an instrument of death.

Never use the cell phone while it is hooked to the electrical outlet! If you are charging the cell phone and a call comes in, unplug it from the charger and outlet.

FORWARD THIS TO THE PEOPLE THAT MATTER IN YOUR LIFE!!!

How to install Java in Windows and Mac Operating system

noreply@blogger.com (Hamid) — Mon, 14 Oct 2013 13:12:00 +0530

How to Install Java (Windows &reg)

Java Development Kit (JDK) 1.7 (officially named Java SE 7), which is freely available from Sun Microsystems (now part of Oracle), is needed for writing Java programs. JDK can be downloaded from the Java mother site @ http://java.sun.com (or http://www.oracle.com/technetwork/java/index.html).

JDK or JRE?

JRE (Java Runtime) is needed for running Java programs. JDK (Java Development Kit), which includes JRE plus the development tools (such as compiler and debugger), is need for writing as well as running Java programs. Since you are supposed to write Java Programs, you should install JDK, which includes JRE.

Step 0(a): Un-Install Older Version(s) of JDK/JRE

I recommend that you install the latest JDK, but it can be messy if you have multiple versions of JDK/JRE.
If you have previously installed older version(s) of JDK/JRE, un-install ALL of them. Run "Control Panel" ⇒ Program and Features ⇒ Un-install programs begin with "Java", such as "Java SE Development Kit" and "Java SE Runtime". If you are not sure whether you have older version(s) of JDK, check!

Step 0(b): Understand Windows' CMD Shell

Programmers need to know how to use CMD shell to issue commands. If you are completely new to CMD, read "Programmer's Survival Guide for Windows".

Step 1: Download JDK

Goto Java SE download site @ http://www.oracle.com/technetwork/java/javase/downloads/index.html.
Click the "Download" button under "JDK" of "Java SE 7".
Choose your operating platform, e.g., Windows x86 for 32-bit Windows OS or Windows x64 for 64-bit Windows OS. You can check whether your Windows OS is 32-bit or 64-bit via "Control Panel" ⇒ System ⇒ Under the "System Type".

Step 2: Install JDK and JRE

Run the downloaded installer (e.g., "jdk-7uxx-windows-i586.exe"), which installs both the JDK (Java Development Kit) and JRE (Java Runtime). By default, the JDK will be installed in directory "C:\Program Files\Java\jdk1.7.0_{xx}", where {xx} denotes the latest upgrade number; and JRE in "C:\Program Files\Java\jre7".
For novices, accept the defaults. Simply click "next"..."next"... to install JDK in "C:\Program Files\Java\jdk1.7.0_{xx}" and JRE in "C:\Program Files\Java\jre7". Take note of you JDK installed directory. I shall refer to the JDK installed directory as <JAVA_HOME>, hereafter, in this article.

(For Advanced Users Only) The default JDK/JRE directories work but I recommend avoiding "Program Files" directory because of that blank character in the directory name. You may change the installed directories for JDK and JRE during installation. I personally installed JDK and all my programming tools in "d:\bin" (instead of "C:\Program Files") for ease of maintenance.

Step 3: Include JDK's "bin" Directory in the PATH

Windows OS searches the current directory and the directories listed in the PATH environment variable for executable programs. JDK's programs (such as Java compiler javac.exe and Java runtime java.exe) reside in directory "<JAVA_HOME>\bin" (where <JAVA_HOME> denotes the JDK installed directory, e.g., C:\Program Files\Java\jdk1.7.0_{xx}). You need to include the "<JAVA_HOME>\bin" directory in the PATH.
To edit the PATH environment variable in Windows 2000/XP/Vista/7/8:

Click "Start" button ⇒ "Control Panel" ⇒ "System" ⇒ (Vista/7/8 only) "Advanced system settings".
Switch to "Advanced" tab ⇒ "Environment Variables..."
In "System Variables" box, scroll down to select "PATH" ⇒ "Edit..."
(CAUTION: Read this paragraph 3 times before doing this step! There is no UNDO) In "Variable value" field, INSERT "c:\Program Files\Java\jdk1.7.0_{xx}\bin" (VERIFY that this is your JDK's binary directory) IN FRONT of all the existing directories, followed by a semi-colon (;) which separates the JDK's binary directory from the rest of the existing directories. DO NOT DELETE any existing entries; otherwise, some existing applications may not run.
```
Variable name  : PATH
Variable value : c:\Program Files\Java\jdk1.7.0_{xx}\bin;[exiting entries]
```

(For Advanced Users Only)
I suggested that you place the JDK bin directory in front of "c:\windows\system32" and "c:\windows". This is because some Windows systems may have an out-dated copy of JDK/JRE in these directories. Do a search for "java.exe", and you will be amazed by the findings.
You could read "Java Applications and Environment Variable" for more discussions about PATH environment variable.
I also recommend that you define an environment variable called JAVA_HOME, which contains the JDK installed directory, and include the JDK bin directory in the PATH via JAVA_HOME, i.e., PATH=%JAVA_HOME%\bin;.....

Step 4: Verify the JDK Installation

Launch a CMD shell (Click "Start" button ⇒ run... ⇒ enter "cmd"; or "Start" button ⇒ All Programs ⇒ Accessories ⇒ Command Prompt).

Issue a "path" command to list the contents of the PATH environment variable. Check the output and make sure that <JAVA_HOME>\bin is listed in the PATH.
```
prompt> path
PATH=c:\Program Files\Java\jdk1.7.0_{xx}\bin;[other entries]
```

Issue the following commands to verify that JDK/JRE are properly installed and display their version:

prompt> java -version
java version "1.7.0_{xx}"
Java(TM) SE Runtime Environment (build 1.7.0_{xx}-b11)
Java HotSpot(TM) Client VM (build 23.3-b01, mixed mode, sharing)
 
prompt> javac -version
javac 1.7.0_{xx}

Step 5: Write a Hello-World Java Program

Create a directory to keep all your works, e.g., d:\myproject, or any directory of your choice. Do NOT save your works in "Desktop" or "Documents" as they are hard to locate. The directory name shall not contain blank or special characters. Use meaningful but short name as it is easier to type.

Launch a programming text editor (such as TextPad or NotePad++). Begin with a new file and enter the following source code. Save the file as "Hello.java", under your work directory (e.g., d:\myproject).

/*
 * First Java program to say Hello
 */
public class Hello {   // Save as "Hello.java" under "d:\myproject"
   public static void main(String[] args) {
      System.out.println("Hello, world!");
   }
}

Step 6: Compile and Run the Hello-World Java Program

To compile the source code "Hello.java":
1. Start a CMD Shell (Click "Start" button ⇒ Select "run..." ⇒ Enter "cmd"; or "Start" button ⇒ All Programs ⇒ Accessories ⇒ Command Prompt).
2. Set the Current Drive to the drive where you saved your source file "Hello.java". For example, suppose that your source file is saved in drive "d", enter "d:" as follow:
```
prompt> d:
D:\xxx>
```
3. Set the Current Working Directory to the directory that you saved your source file via the cd (Change Directory) command. For example, suppose that your source file is saved in directory "d:\myproject".
```
D:\xxx> cd \myproject
D:\myproject>
```
4. Issue a dir (List Directory) command to confirm that your source file is present in the current directory.
```
D:\myproject> dir
......
08-May-XX  06:25 PM               277 Hello.java
......
```
5. Invoke the JDK compiler "javac" to compile the source code "Hello.java".
```
D:\myproject> javac Hello.java
```
  The compilation is successful if the command prompt returns. Otherwise, error messages would be shown. Correct the errors in your source file and re-compile. Check "Common JDK Installation Errors", if you encounter problem compiling your program.
6. The output of the compilation is a Java class called "Hello.class". Issue a dir (List Directory) command again to check for the output.
```
D:\myproject> dir
......
xx-xxx-xx  01:53 PM               416 Hello.class
xx-xxx-xx  06:25 PM               277 Hello.java
......
```
To run the program, invoke the Java Runtime "java":
```
D:\myproject> java Hello
Hello, world!
```

Step 7: (Optional) Download JDK API Documentation, Samples and Demos

The JDK download does not include the documentation, which needs to be downloaded separately. In the past, I always insist that my students should have a local copy of JDK API Documentation. But, today, you can easily access the online copy by googling "JDK 7 Documentation".
To install JDK API documentation:

From the Java SE download page (@ http://www.oracle.com/technetwork/java/javase/downloads/index.html), look for "Java SE 7 Documentation" (under "Additional Resources") ⇒ Download the zip-file (e.g., "jdk-7....zip" - about 57MB).
Unzip into the <JAVA_HOME> (JDK installed directory). The documentation will be unzipped into "<$JAVA_HOME>\docs". Browse the JDK documentation by opening "<JAVA_HOME>\docs\index.html".

You should also download the "JDK Samples and Demos" from the Java SE download site.

Step 8: (For Advanced Users Only) JDK's Source Code

Source code for JDK is provided and kept in "<JAVA_HOME>\src.zip". I strongly recommend that you to go through some of the source files such as "String.java", "Math.java", and "Integer.java", under "java\lang".

1.1 Using TextPad for Java Programming (on Windows)

TextPad (@ www.textpad.com) is an excellent programming text editor for writing toy Java programs. It can be configured to couple with the JDK, hence, bypassing the CMD shell. From the TextPad editor, you can invoke the JDK compiler/runtime directly via "Tools" menu ⇒ External Tools ⇒ "Compile Java" or "Run Java Application". Take note of the keyboard shortcuts - Ctrl+1 for compile and Ctrl+2 for run.
If you cannot find these commands in the "Tools" menu, goto "Configure" ⇒ Preferences... ⇒ Tools ⇒ Add ⇒ JDK Commands. You can also configure the properties of "compile" and "run" there, such as prompting for command-line arguments.

1.2 Using NotePad++ for Java Programming (on Windows)

Notepad++ (@ http://notepad-plus-plus.org) is a free and open-source programming editor.
You can use NotePad++ to input Java source code, and compile and run the Java program under CMD shell.

NotePad++ Customization and Tips

You can customize Notepad++ to compile and run Java programs with hot-keys.

How Google Works

noreply@blogger.com (Hamid) — Sun, 6 Oct 2013 12:56:00 +0530

The Google Search Engine.

Today, Google's popularity continues to grow. In 2007, the company surpassed Microsoft as the most visited site on the Web [source: Kopytoff]. The company's influence on the Web is undeniable. Practically every webmaster wants his or her site listed high on Google's search engine results pages (SERPs), because it almost always translates into more traffic on the corresponding Web site. Google has also acquired other Internet companies, ranging from blogging services to the video-sharing site YouTube. For a while, the company's search technology even powered rival companies' search engines -- Yahoo! relied on Google searches for nearly four years until developing its own search engine technologies in 2004 [sources: Google; Hu and Olsen].
Google's search engine is a powerful tool. Without search engines like Google, it would be practically impossible to find the information you need when you browse the Web. Like all search engines, Google uses a special algorithm to generate search results. While Google shares general facts about its algorithm, the specifics are a company secret. This helps Google remain competitive with other search engines on the Web and reduces the chance of someone finding out how to abuse the system.
Google uses automated programs called spiders or crawlers, just like most search engines. Also like other search engines, Google has a large index of keywords and where those words can be found. What sets Google apart is how it ranks search results, which in turn determines the order Google displays results on its search engine results page (SERP). Google uses a trademarked algorithm called PageRank, which assigns each Web page a relevancy score.
A Web page's PageRank depends on a few factors:

The frequency and location of keywords within the Web page: If the keyword only appears once within the body of a page, it will receive a low score for that keyword.
How long the Web page has existed: People create new Web pages every day, and not all of them stick around for long. Google places more value on pages with an established history.
The number of other Web pages that link to the page in question: Google looks at how many Web pages link to a particular site to determine its relevance.

Out of these three factors, the third is the most important. It's easier to understand it with an example. Let's look at a search for the terms "Planet Earth."

As more Web pages link to Discovery's Planet Earth page, the Discovery page's rank increases. When Discovery's page ranks higher than other pages, it shows up at the top of the Google search results page.
Because Google looks at links to a Web page as a vote, it's not easy to cheat the system. The best way to make sure your Web page is high up on Google's search results is to provide great content so that people will link back to your page. The more links your page gets, the higher its PageRank score will be. If you attract the attention of sites with a high PageRank score, your score will grow faster.
Google initiated an experiment with its search engine in 2008. For the first time, Google is allowing a group of beta testers to change the ranking order of search results. In this experiment, beta testers can promote or demote search results and tailor their search experience so that it's more personally relevant. Google executives say there's no guarantee that the company will ever implement this feature into the search engine globally.

Continue Reading..,

How Google Search Engine Works

noreply@blogger.com (Hamid) — Sun, 6 Oct 2013 12:54:00 +0530

Internet search engines are special sites on the Web that are designed to help people find information stored on other sites. There are differences in the ways various search engines work, but they all perform three basic tasks:

They search the Internet -- or select pieces of the Internet -- based on important words.
They keep an index of the words they find, and where they find them.
They allow users to look for words or combinations of words found in that index.

Early search engines held an index of a few hundred thousand pages and documents, and received maybe one or two thousand inquiries each day. Today, a top search engine will index hundreds of millions of pages, and respond to tens of millions of queries per day. In this article, we'll tell you how these major tasks are performed, and how Internet search engines put the pieces together in order to let you find the information you need on the Web.

Web Crawling

When most people talk about Internet search engines, they really mean World Wide Web search engines. Before the Web became the most visible part of the Internet, there were already search engines in place to help people find information on the Net. Programs with names like "gopher" and "Archie" kept indexes of files stored on servers connected to the Internet, and dramatically reduced the amount of time required to find programs and documents. In the late 1980s, getting serious value from the Internet meant knowing how to use gopher, Archie, Veronica and the rest.
Today, most Internet users limit their searches to the Web, so we'll limit this article to search engines that focus on the contents of Web pages.
Before a search engine can tell you where a file or document is, it must be found. To find information on the hundreds of millions of Web pages that exist, a search engine employs special software robots, called spiders, to build lists of the words found on Web sites. When a spider is building its lists, the process is called Web crawling. (There are some disadvantages to calling part of the Internet the World Wide Web -- a large set of arachnid-centric names for tools is one of them.) In order to build and maintain a useful list of words, a search engine's spiders have to look at a lot of pages.
How does any spider start its travels over the Web? The usual starting points are lists of heavily used servers and very popular pages. The spider will begin with a popular site, indexing the words on its pages and following every link found within the site. In this way, the spidering system quickly begins to travel, spreading out across the most widely used portions of the Web.
Google began as an academic search engine. In the paper that describes how the system was built, Sergey Brin and Lawrence Page give an example of how quickly their spiders can work. They built their initial system to use multiple spiders, usually three at one time. Each spider could keep about 300 connections to Web pages open at a time. At its peak performance, using four spiders, their system could crawl over 100 pages per second, generating around 600 kilobytes of data each second.
Keeping everything running quickly meant building a system to feed necessary information to the spiders. The early Google system had a server dedicated to providing URLs to the spiders. Rather than depending on an Internet service provider for the domain name server (DNS) that translates a server's name into an address, Google had its own DNS, in order to keep delays to a minimum.
When the Google spider looked at an HTML page, it took note of two things:

The words within the page
Where the words were found

Words occurring in the title, subtitles, meta tags and other positions of relative importance were noted for special consideration during a subsequent user search. The Google spider was built to index every significant word on a page, leaving out the articles "a," "an" and "the." Other spiders take different approaches.

Meta Tags

Meta tags allow the owner of a page to specify key words and concepts under which the page will be indexed. This can be helpful, especially in cases in which the words on the page might have double or triple meanings -- the meta tags can guide the search engine in choosing which of the several possible meanings for these words is correct. There is, however, a danger in over-reliance on meta tags, because a careless or unscrupulous page owner might add meta tags that fit very popular topics but have nothing to do with the actual contents of the page. To protect against this, spiders will correlate meta tags with page content, rejecting the meta tags that don't match the words on the page.

Building the Index

Once the spiders have completed the task of finding information on Web pages (and we should note that this is a task that is never actually completed -- the constantly changing nature of the Web means that the spiders are always crawling), the search engine must store the information in a way that makes it useful. There are two key components involved in making the gathered data accessible to users:

The information stored with the data
The method by which the information is indexed

In the simplest case, a search engine could just store the word and the URL where it was found. In reality, this would make for an engine of limited use, since there would be no way of telling whether the word was used in an important or a trivial way on the page, whether the word was used once or many times or whether the page contained links to other pages containing the word. In other words, there would be no way of building the ranking list that tries to present the most useful pages at the top of the list of search results.An index has a single purpose: It allows information to be found as quickly as possible. There are quite a few ways for an index to be built, but one of the most effective ways is to build a hash table. In hashing, a formula is applied to attach a numerical value to each word. The formula is designed to evenly distribute the entries across a predetermined number of divisions. This numerical distribution is different from the distribution of words across the alphabet, and that is the key to a hash table's effectiveness.

Building a Search

Searching through an index involves a user building a query and submitting it through the search engine. The query can be quite simple, a single word at minimum. Building a more complex query requires the use of Boolean operators that allow you to refine and extend the terms of the search.
The Boolean operators most often seen are:

AND - All the terms joined by "AND" must appear in the pages or documents. Some search engines substitute the operator "+" for the word AND.
OR - At least one of the terms joined by "OR" must appear in the pages or documents.
NOT - The term or terms following "NOT" must not appear in the pages or documents. Some search engines substitute the operator "-" for the word NOT.
FOLLOWED BY - One of the terms must be directly followed by the other.
NEAR - One of the terms must be within a specified number of words of the other.
Quotation Marks - The words between the quotation marks are treated as a phrase, and that phrase must be found within the document or file.

courtesy:HowStuffWorks.com

10 Easy Steps to build a Website

noreply@blogger.com (Hamid) — Thu, 3 Oct 2013 23:19:00 +0530

step 1:

Selecting a domain name For Your Website:

Preselect a domain name but 1st find the keywords / key phrases that pertain to your business or service. if you are not familiar with what a key word, key phrase or long tail keyword is chick here keywords. incorporate your keywords into your domain name. your domain name does not have to be your business name.

step 2:

Check availability of your selected domain name For Your Website:

Use one of the two services listed on the right side bar to determine if your domain name has been taken. it is a free service. in godaddy click on find your domain or in hostgator click on Domains. if you find a domain you like lock it in so no one else can steal it from you. then follow the instructions on having your domain hosted.

step 3:

Build A Website:

determine what type of platform / website you want to build. I use standard html and word press. there are free templates that come with your hosting sites our you can create your own design. design your website prior to publishing / uploading it to your hosting company.

step 4:

SEO Optimization For Your Website:

Size your image files to match your webpage size also name your files with a name that is relevant to your website image sizes. use h1 h2 h3 h4 tags. paragraph your text. provide links both internal and external. have some relevant back links to your site (these are links for other websites linked back to your website).

step 5:

Website Title Line, Keywords And Description:

Keep Your Title Line Between 20 And 60 Characters And Use Your Keywords / Key Phrases In It. Don't Copy Your Domain Name. Your Website Description Should Also Use Your Keywords. The Length Should Be No Longer Than 140 Characters. Don't Over Stuff Your Keywords In Your Website Or Description. In The Head Section Of Your Source Code Of Your Website Make Sure You Have A Keyword Meta Tag. Add Your Keywords / Key Phrases That Are Relevant To Your Website Only Once And In The Order That They Are Mostly Used / Density. Use 50 Max. Use One Of The Free Website Tools To Check The Density.

step 6:

Website Video:

Google Owns YouTube. Shoot Or Build A Video. Windows Has A Video Maker In It. Once Made Upload It To YouTube Or Another Video Hosting Platform. Open It And Copy The Embedment File. In Your Website Program Install Your Embedment File Into Your Website. Here Is An Example. Video How To Build A Website

step 7:

Indexing Your Website For Search Engines & Directories:

Index Your Website So It Will Push It Through The Search Engines Faster. It May Take 24 Hrs To 8 Days But To Fully Index Your Site and All Its Links May Take Up To 90 Days.

step 8:

Website 1st Page Ranking Using Localization:

Localizing Your Search Results Will Make It Easier To Obtain 1st Page Ranking For Your Website. Most Clients / Customers Will Not Venture Past The 1st Or 2nd Page. To Do This You Might Want To Add To Your Domain Name The City That You Want To Do Business In And In Some Cases The State or You Can Create Another Index Or Html Folder Under Your Root Folder (Domain Name).

step 9:

Website 1st Page Ranking Using Link Building:

Link Building can improve your Website Ranking With Out Localizing Or Long Tail Key Phrases.
It Is Important When Link Building To Use Relevant Links Both In and Out. Make Sure You Are
Selecting Linked Sites That Themselves Have A High Page Ranking. A Low Ranked Site Can
Weight Your Website Down.
Here Is A Site Link That We Recommend For Finding Great Back Links. Link Building Made Easy

step 10:

Website 1st Page Ranking Using Blogs:

You Can Create a Blog Website using Word Press Or Coral, Both Are Great Blog Platforms,

they offer free templates and lots of free plug ins including SEO plug ins. Blog website templates

are search engine friendly and help in page ranking. search engines like new content and a blog site

will give you that. down fall is once your site reaches front page ranking your site will
be blasted with bloggers attaching to your blog website. this works like backing for them
in their comment like spam will have their website link.
so be prepaid to receive allot of computer generated comments.

Create Your Own Website with Wix - No Coding Needed

HOW TO READ BAR CODES

noreply@blogger.com (Hamid) — Tue, 1 Oct 2013 15:42:00 +0530

HOW TO READ BAR CODES...(everyone must know)

ALWAYS READ THE LABELS ON THE FOODS YOU BUY--NO MATTER WHAT THE FRONT OF THE BOX OR PACKAGE SAYS, TURN IT OVER AND READ THE BACK---CAREFULLY!

With all the food and pet products now coming from China, it is best to make sure you read label at the supermarket and especially when buying food products. Many products no longer show where they were made, only give where the distributor is located. The whole world is concerned about China-made "black- hearted goods".

Can you differentiate which one is made in Taiwan or China ?

The world is also concerned about GMO (Genetically Modified Organism) foods; steroid fed animals (ex: 45 days old

broiler chicken).

It is important to read the bar code to track its origin. How to read Bar Codes ....interesting !

If the first 3 digits of the bar code are 690, 691 or 692, the product is MADE IN CHINA. 471 is Made in Taiwan .

If the first 3 digits of the barcode are

00-09 then it's made or sourced in USA

This is our right to know, but the government and related departments never educate the public, therefore we have to RESCUE ourselves.

Nowadays, Chinese businessmen know that consumers do not prefer products"MADE IN CHINA", so they don't show from which country it is made. However, you may now refer to the barcode - remember if the first 3 digits are:

890......MADE IN INDIA

690, 691, 692 ... then it is MADE IN CHINA

00 - 09 ... USA and CANADA

30 - 37 ... FRANCE

40 - 44 ... GERMANY

471 ........ Taiwan

49 .......... JAPAN

50 .......... UK

C++ Tuorial Part-I

noreply@blogger.com (Hamid) — Sun, 29 Sep 2013 12:59:00 +0530

C++ Tutorial

C++ is a middle-level programming language developed by Bjarne Stroustrup starting in 1979 at Bell Labs. C++ runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.
This reference will take you through simple and practical approach while learning C++ Programming language.

Audience

This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to C++ Programming languages.

Prerequisites

Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about what is a computer program and what is a computer programming language?

Compile/Execute C++ Programs

For most of the examples given in this tutorial, you will find Try it option to compile and execute C++ programs online, so just make use of it and enjoy your learning.
Try the following example using Try it option available at the top right corner of the below sample code box:

#include <iostream>
using namespace std;

int main()
{
   cout << "Hello World";
   return 0;
}

C++ is a statically typed, compiled, general-purpose, case-sensitive, free-form programming language that supports procedural, object-oriented, and generic programming.
C++ is regarded as a middle-level language, as it comprises a combination of both high-level and low-level language features.
C++ was developed by Bjarne Stroustrup starting in 1979 at Bell Labs in Murray Hill, New Jersey, as an enhancement to the C language and originally named C with Classes but later it was renamed C++ in 1983.
C++ is a superset of C, and that virtually any legal C program is a legal C++ program.
Note: A programming language is said to use static typing when type checking is performed during compile-time as opposed to run-time.

Object-Oriented Programming

C++ fully supports object-oriented programming, including the four pillars of object-oriented development:

Encapsulation
Data hiding
Inheritance
Polymorphism

Standard Libraries

Standard C++ consists of three important parts:

The core language giving all the building blocks including variables, data types and literals, etc.
The C++ Standard Library giving a rich set of functions manipulating files, strings, etc.
The Standard Template Library (STL) giving a rich set of methods manipulating data structures, etc.

The ANSI Standard

The ANSI standard is an attempt to ensure that C++ is portable -- that code you write for Microsoft's compiler will compile without errors, using a compiler on a Mac, UNIX, a Windows box, or an Alpha.
The ANSI standard has been stable for a while, and all the major C++ compiler manufacturers support the ANSI standard.

Learning C++

The most important thing to do when learning C++ is to focus on concepts and not get lost in language technical details.
The purpose of learning a programming language is to become a better programmer; that is, to become more effective at designing and implementing new systems and at maintaining old ones.
C++ supports a variety of programming styles. You can write in the style of Fortran, C, Smalltalk, etc., in any language. Each style can achieve its aims effectively while maintaining runtime and space efficiency.

Use of C++

C++ is used by hundreds of thousands of programmers in essentially every application domain.
C++ is being highly used to write device drivers and other softwares that rely on direct manipulation of hardware under realtime constraints.
C++ is widely used for teaching and research because it is clean enough for successful teaching of basic concepts.
Anyone who has used either an Apple Macintosh or a PC running Windows has indirectly used C++ because the primary user interfaces of these systems are written in C++.

C++ Basic Syntax

When we consider a C++ program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods and instant variables mean.

Object - Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors - wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/blueprint that describes the behaviors/states that object of its type support.
Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant variables.

C++ Program Structure:

Let us look at a simple code that would print the words Hello World.

#include <iostream>
using namespace std;

// main() is where program execution begins.

int main()
{
   cout << "Hello World"; // prints Hello World
   return 0;
}

Let us look various parts of the above program:

The C++ language defines several headers, which contain information that is either necessary or useful to your program. For this program, the header <iostream> is needed.
The line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively recent addition to C++.
The next line // main() is where program execution begins. is a single-line comment available in C++. Single-line comments begin with // and stop at the end of the line.
The line int main() is the main function where program execution begins.
The next line cout << "This is my first C++ program."; causes the message "This is my first C++ program" to be displayed on the screen.
The next line return 0; terminates main( )function and causes it to return the value 0 to the calling process.

Compile & Execute C++ Program:

Let's look at how to save the file, compile and run the program. Please follow the steps given below:

Open a text editor and add the code as above.
Save the file as: hello.cpp
Open a command prompt and go to the directory where you saved the file.
Type 'g++ hello.cpp ' and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line and would generate a.out executable file.
Now, type ' a.out' to run your program.
You will be able to see ' Hello World ' printed on the window.

$ g++ hello.cpp
$ ./a.out
Hello World

Make sure that g++ is in your path and that you are running it in the directory containing file hello.cpp.
You can compile C/C++ programs using makefile. For more details, you can check Makefile Tutorial.

Semicolons & Blocks in C++:

In C++, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.
For example, following are three different statements:

x = y;
y = y+1;
add(x, y);

A block is a set of logically connected statements that are surrounded by opening and closing braces. For example:

{
   cout << "Hello World"; // prints Hello World
   return 0;
}

C++ does not recognize the end of the line as a terminator. For this reason, it does not matter where on a line you put a statement. For example:

x = y;
y = y+1;
add(x, y);

is the same as

x = y; y = y+1; add(x, y);

C++ Identifiers:

A C++ identifier is a name used to identify a variable, function, class, module, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).
C++ does not allow punctuation characters such as @, $, and % within identifiers. C++ is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C++.
Here are some examples of acceptable identifiers:

mohd       zara    abc   move_name  a_123
myname50   _temp   j     a23b9      retVal

C++ Keywords:

The following list shows the reserved words in C++. These reserved words may not be used as constant or variable or any other identifier names.

asm	else	new	this
auto	enum	operator	throw
bool	explicit	private	true
break	export	protected	try
case	extern	public	typedef
catch	false	register	typeid
char	float	reinterpret_cast	typename
class	for	return	union
const	friend	short	unsigned
const_cast	goto	signed	using
continue	if	sizeof	virtual
default	inline	static	void
delete	int	static_cast	volatile
do	long	struct	wchar_t
double	mutable	switch	while
dynamic_cast	namespace	template

Trigraphs:

A few characters have an alternative representation, called a trigraph sequence. A trigraph is a three-character sequence that represents a single character and the sequence always starts with two question marks.
Trigraphs are expanded anywhere they appear, including within string literals and character literals, in comments, and in preprocessor directives.
Following are most frequently used trigraph sequences:

Trigraph	Replacement
??=	#
??/	\
??'	^
??(	[
??)	]
??!	\|
??<	{
??>	}
??-	~

All the compilers do not support trigraphs and they are not advised to be used because of their confusing nature.

Whitespace in C++:

A line containing only whitespace, possibly with a comment, is known as a blank line, and C++ compiler totally ignores it.
Whitespace is the term used in C++ to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins. Therefore, in the statement,

int age;

there must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the statement

fruit = apples + oranges;   // Get the total fruit

no whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose.
Click here to Learn About C++ Object Oriented Part>>

C++ Object Oriented

C++ Tutorial Part-II

noreply@blogger.com (Hamid) — Sun, 29 Sep 2013 12:58:00 +0530

C++ Classes and Objects

The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types.
A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.

C++ Class Definitions:

When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object.
A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. A class definition must be followed either by a semicolon or a list of declarations. For example, we defined the Box data type using the keyword class as follows:

class Box
{
   public:
      double length;   // Length of a box
      double breadth;  // Breadth of a box
      double height;   // Height of a box
};

The keyword public determines the access attributes of the members of the class that follow it. A public member can be accessed from outside the class anywhere within the scope of the class object. You can also specify the members of a class as private or protected which we will discuss in a sub-section.

Define C++ Objects:

A class provides the blueprints for objects, so basically an object is created from a class. We declare objects of a class with exactly the same sort of declaration that we declare variables of basic types. Following statements declare two objects of class Box:

Box Box1;          // Declare Box1 of type Box
Box Box2;          // Declare Box2 of type Box

Both of the objects Box1 and Box2 will have their own copy of data members.

Accessing the Data Members:

The public data members of objects of a class can be accessed using the direct member access operator (.). Let us try the following example to make the things clear:

#include <iostream>

using namespace std;

class Box
{
   public:
      double length;   // Length of a box
      double breadth;  // Breadth of a box
      double height;   // Height of a box
};

int main( )
{
   Box Box1;        // Declare Box1 of type Box
   Box Box2;        // Declare Box2 of type Box
   double volume = 0.0;     // Store the volume of a box here
 
   // box 1 specification
   Box1.height = 5.0; 
   Box1.length = 6.0; 
   Box1.breadth = 7.0;

   // box 2 specification
   Box2.height = 10.0;
   Box2.length = 12.0;
   Box2.breadth = 13.0;
   // volume of box 1
   volume = Box1.height * Box1.length * Box1.breadth;
   cout << "Volume of Box1 : " << volume <<endl;

   // volume of box 2
   volume = Box2.height * Box2.length * Box2.breadth;
   cout << "Volume of Box2 : " << volume <<endl;
   return 0;
}

When the above code is compiled and executed, it produces the following result:

Volume of Box1 : 210
Volume of Box2 : 1560

It is important to note that private and protected members can not be accessed directly using direct member access operator (.). We will learn how private and protected members can be accessed.

Classes & Objects in Detail:

So far, you have got very basic idea about C++ Classes and Objects. There are further interesting concepts related to C++ Classes and Objects which we will discuss in various sub-sections listed below:

Concept	Description
Class member functions	A member function of a class is a function that has its definition or its prototype within the class definition like any other variable.
Class access modifiers	A class member can be defined as public, private or protected. By default members would be assumed as private.
Constructor & destructor	A class constructor is a special function in a class that is called when a new object of the class is created. A destructor is also a special function which is called when created object is deleted.
C++ copy constructor	The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously.
C++ friend functions	A friend function is permitted full access to private and protected members of a class.
C++ inline functions	With an inline function, the compiler tries to expand the code in the body of the function in place of a call to the function.
The this pointer in C++	Every object has a special pointer this which points to the object itself.
Pointer to C++ classes	A pointer to a class is done exactly the same way a pointer to a structure is. In fact a class is really just a structure with functions in it.
Static members of a class	Both data members and function members of a class can be declared as static.

C++ Inheritance

One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.
When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.
The idea of inheritance implements the is a relationship. For example, mammal IS-A animal, dog IS-A mammal hence dog IS-A animal as well and so on.

Base & Derived Classes:

A class can be derived from more than one classes, which means it can inherit data and functions from multiple base classes. To define a derived class, we use a class derivation list to specify the base class(es). A class derivation list names one or more base classes and has the form:

class derived-class: access-specifier base-class

Where access-specifier is one of public, protected, or private, and base-class is the name of a previously defined class. If the access-specifier is not used, then it is private by default.
Consider a base class Shape and its derived class Rectangle as follows:

#include <iostream>
 
using namespace std;

// Base class
class Shape 
{
   public:
      void setWidth(int w)
      {
         width = w;
      }
      void setHeight(int h)
      {
         height = h;
      }
   protected:
      int width;
      int height;
};

// Derived class
class Rectangle: public Shape
{
   public:
      int getArea()
      { 
         return (width * height); 
      }
};

int main(void)
{
   Rectangle Rect;
 
   Rect.setWidth(5);
   Rect.setHeight(7);

   // Print the area of the object.
   cout << "Total area: " << Rect.getArea() << endl;

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Total area: 35

Access Control and Inheritance:

A derived class can access all the non-private members of its base class. Thus base-class members that should not be accessible to the member functions of derived classes should be declared private in the base class.
We can summarize the different access types according to who can access them in the following way:

Access	public	protected	private
Same class	yes	yes	yes
Derived classes	yes	yes	no
Outside classes	yes	no	no

A derived class inherits all base class methods with the following exceptions:

Constructors, destructors and copy constructors of the base class.
Overloaded operators of the base class.
The friend functions of the base class.

Type of Inheritance:

When deriving a class from a base class, the base class may be inherited through public, protected or private inheritance. The type of inheritance is specified by the access-specifier as explained above.
We hardly use protected or private inheritance, but public inheritance is commonly used. While using different type of inheritance, following rules are applied:

Public Inheritance: When deriving a class from a public base class, public members of the base class become public members of the derived class and protected members of the base class become protected members of the derived class. A base class's private members are never accessible directly from a derived class, but can be accessed through calls to the public and protected members of the base class.
Protected Inheritance: When deriving from a protected base class, public and protected members of the base class become protected members of the derived class.
Private Inheritance: When deriving from a private base class, public and protected members of the base class become private members of the derived class.

Multiple Inheritances:

A C++ class can inherit members from more than one class and here is the extended syntax:

class derived-class: access baseA, access baseB....

Where access is one of public, protected, or private and would be given for every base class and they will be separated by comma as shown above. Let us try the following example:

#include <iostream>
 
using namespace std;

// Base class Shape
class Shape 
{
   public:
      void setWidth(int w)
      {
         width = w;
      }
      void setHeight(int h)
      {
         height = h;
      }
   protected:
      int width;
      int height;
};

// Base class PaintCost
class PaintCost 
{
   public:
      int getCost(int area)
      {
         return area * 70;
      }
};

// Derived class
class Rectangle: public Shape, public PaintCost
{
   public:
      int getArea()
      { 
         return (width * height); 
      }
};

int main(void)
{
   Rectangle Rect;
   int area;
 
   Rect.setWidth(5);
   Rect.setHeight(7);

   area = Rect.getArea();
   
   // Print the area of the object.
   cout << "Total area: " << Rect.getArea() << endl;

   // Print the total cost of painting
   cout << "Total paint cost: $" << Rect.getCost(area) << endl;

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Total area: 35
Total paint cost: $2450

C++ Overloading (Operator and Function)

C++ allows you to specify more than one definition for a function name or an operator in the same scope, which is called function overloading and operator overloading respectively.
An overloaded declaration is a declaration that had been declared with the same name as a previously declared declaration in the same scope, except that both declarations have different arguments and obviously different definition (implementation).
When you call an overloaded function or operator, the compiler determines the most appropriate definition to use by comparing the argument types you used to call the function or operator with the parameter types specified in the definitions. The process of selecting the most appropriate overloaded function or operator is called overload resolution.

Function overloading in C++:

You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You can not overload function declarations that differ only by return type.
Following is the example where same function print() is being used to print different data types:
#include <iostream> using namespace std; class printData { public: void print(int i) { cout << "Printing int: " << i << endl; } void print(double f) { cout << "Printing float: " << f << endl; } void print(char* c) { cout << "Printing character: " << c << endl; } }; int main(void) { printData pd; // Call print to print integer pd.print(5); // Call print to print float pd.print(500.263); // Call print to print character pd.print("Hello C++"); return 0; } When the above code is compiled and executed, it produces the following result:
Printing int: 5 Printing float: 500.263 Printing character: Hello C++

Operators overloading in C++:

You can redefine or overload most of the built-in operators available in C++. Thus a programmer can use operators with user-defined types as well.
Overloaded operators are functions with special names the keyword operator followed by the symbol for the operator being defined. Like any other function, an overloaded operator has a return type and a parameter list.
Box operator+(const Box&); declares the addition operator that can be used to add two Box objects and returns final Box object. Most overloaded operators may be defined as ordinary non-member functions or as class member functions. In case we define above function as non-member function of a class then we would have to pass two arguments for each operand as follows:
Box operator+(const Box&, const Box&); Following is the example to show the concept of operator over loading using a member function. Here an object is passed as an argument whose properties will be accessed using this object, the object which will call this operator can be accessed using this operator as explained below:
#include <iostream> using namespace std; class Box { public: double getVolume(void) { return length * breadth * height; } void setLength( double len ) { length = len; } void setBreadth( double bre ) { breadth = bre; } void setHeight( double hei ) { height = hei; } // Overload + operator to add two Box objects. Box operator+(const Box& b) { Box box; box.length = this->length + b.length; box.breadth = this->breadth + b.breadth; box.height = this->height + b.height; return box; } private: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box }; // Main function for the program int main( ) { Box Box1; // Declare Box1 of type Box Box Box2; // Declare Box2 of type Box Box Box3; // Declare Box3 of type Box double volume = 0.0; // Store the volume of a box here // box 1 specification Box1.setLength(6.0); Box1.setBreadth(7.0); Box1.setHeight(5.0); // box 2 specification Box2.setLength(12.0); Box2.setBreadth(13.0); Box2.setHeight(10.0); // volume of box 1 volume = Box1.getVolume(); cout << "Volume of Box1 : " << volume <<endl; // volume of box 2 volume = Box2.getVolume(); cout << "Volume of Box2 : " << volume <<endl; // Add two object as follows: Box3 = Box1 + Box2; // volume of box 3 volume = Box3.getVolume(); cout << "Volume of Box3 : " << volume <<endl; return 0; } When the above code is compiled and executed, it produces the following result:
Volume of Box1 : 210 Volume of Box2 : 1560 Volume of Box3 : 5400

Overloadable/Non-overloadableOperators:

Following is the list of operators which can be overloaded:

+	-	*	/	%	^
&	\|	~	!	,	=
<	>	<=	>=	++	--
<<	>>	==	!=	&&	\|\|
+=	-=	/=	%=	^=	&=
\|=	*=	<<=	>>=	[]	()
->	->*	new	new []	delete	delete []

Following is the list of operators, which can not be overloaded:

Polymorphism in C++

The word polymorphism means having many forms. Typically, polymorphism occurs when there is a hierarchy of classes and they are related by inheritance.
C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function.
Consider the following example where a base class has been derived by other two classes:

#include <iostream> 
using namespace std;
 
class Shape {
   protected:
      int width, height;
   public:
      Shape( int a=0, int b=0)
      {
         width = a;
         height = b;
      }
      int area()
      {
         cout << "Parent class area :" <<endl;
         return 0;
      }
};
class Rectangle: public Shape{
   public:
      Rectangle( int a=0, int b=0)
      {
        Shape(a, b); 
      }
      int area ()
      { 
         cout << "Rectangle class area :" <<endl;
         return (width * height); 
      }
};
class Triangle: public Shape{
   public:
      Triangle( int a=0, int b=0)
      {
        Shape(a, b); 
      }
      int area ()
      { 
         cout << "Rectangle class area :" <<endl;
         return (width * height / 2); 
      }
};
// Main function for the program
int main( )
{
   Shape *shape;
   Rectangle rec(10,7);
   Triangle  tri(10,5);

   // store the address of Rectangle
   shape = &rec;
   // call rectangle area.
   shape->area();

   // store the address of Triangle
   shape = &tri;
   // call triangle area.
   shape->area();
   
   return 0;
}

When the above code is compiled and executed, it produces the following result:

Parent class area
Parent class area

The reason for the incorrect output is that the call of the function area() is being set once by the compiler as the version defined in the base class. This is called static resolution of the function call, or static linkage - the function call is fixed before the program is executed. This is also sometimes called early binding because the area() function is set during the compilation of the program.
But now, let's make a slight modification in our program and precede the declaration of area() in the Shape class with the keyword virtual so that it looks like this:

class Shape {
   protected:
      int width, height;
   public:
      Shape( int a=0, int b=0)
      {
         width = a;
         height = b;
      }
      virtual int area()
      {
         cout << "Parent class area :" <<endl;
         return 0;
      }
};

After this slight modification, when the previous example code is compiled and executed, it produces the following result:

Rectangle class area
Triangle class area

This time, the compiler looks at the contents of the pointer instead of it's type. Hence, since addresses of objects of tri and rec classes are stored in *shape the respective area() function is called.
As you can see, each of the child classes has a separate implementation for the function area(). This is how polymorphism is generally used. You have different classes with a function of the same name, and even the same parameters, but with different implementations.

Virtual Function:

A virtual function is a function in a base class that is declared using the keyword virtual. Defining in a base class a virtual function, with another version in a derived class, signals to the compiler that we don't want static linkage for this function.
What we do want is the selection of the function to be called at any given point in the program to be based on the kind of object for which it is called. This sort of operation is referred to as dynamic linkage, or late binding.

Pure Virtual Functions:

It's possible that you'd want to include a virtual function in a base class so that it may be redefined in a derived class to suit the objects of that class, but that there is no meaningful definition you could give for the function in the base class.
We can change the virtual function area() in the base class to the following:

class Shape {
   protected:
      int width, height;
   public:
      Shape( int a=0, int b=0)
      {
         width = a;
         height = b;
      }
      // pure virtual function
      virtual int area() = 0;
};

The = 0 tells the compiler that the function has no body and above virtual function will be called pure virtual function.

Data Abstraction in C++

Data abstraction refers to, providing only essential information to the outside world and hiding their background details, i.e., to represent the needed information in program without presenting the details.
Data abstraction is a programming (and design) technique that relies on the separation of interface and implementation.
Let's take one real life example of a TV, which you can turn on and off, change the channel, adjust the volume, and add external components such as speakers, VCRs, and DVD players, BUT you do not know its internal details, that is, you do not know how it receives signals over the air or through a cable, how it translates them, and finally displays them on the screen.
Thus, we can say a television clearly separates its internal implementation from its external interface and you can play with its interfaces like the power button, channel changer, and volume control without having zero knowledge of its internals.
Now, if we talk in terms of C++ Programming, C++ classes provides great level of data abstraction. They provide sufficient public methods to the outside world to play with the functionality of the object and to manipulate object data, i.e., state without actually knowing how class has been implemented internally.
For example, your program can make a call to the sort() function without knowing what algorithm the function actually uses to sort the given values. In fact, the underlying implementation of the sorting functionality could change between releases of the library, and as long as the interface stays the same, your function call will still work.
In C++, we use classes to define our own abstract data types (ADT). You can use the cout object of class ostream to stream data to standard output like this:

#include <iostream>
using namespace std;

int main( )
{
   cout << "Hello C++" <<endl;
   return 0;
}

Here, you don't need to understand how cout displays the text on the user's screen. You need to only know the public interface and the underlying implementation of cout is free to change.

Access Labels Enforce Abstraction:

In C++, we use access labels to define the abstract interface to the class. A class may contain zero or more access labels:

Members defined with a public label are accessible to all parts of the program. The data-abstraction view of a type is defined by its public members.
Members defined with a private label are not accessible to code that uses the class. The private sections hide the implementation from code that uses the type.

There are no restrictions on how often an access label may appear. Each access label specifies the access level of the succeeding member definitions. The specified access level remains in effect until the next access label is encountered or the closing right brace of the class body is seen.

Benefits of Data Abstraction:

Data abstraction provides two important advantages:

Class internals are protected from inadvertent user-level errors, which might corrupt the state of the object.
The class implementation may evolve over time in response to changing requirements or bug reports without requiring change in user-level code.

By defining data members only in the private section of the class, the class author is free to make changes in the data. If the implementation changes, only the class code needs to be examined to see what affect the change may have. If data are public, then any function that directly accesses the data members of the old representation might be broken.

Data Abstraction Example:

Any C++ program where you implement a class with public and private members is an example of data abstraction. Consider the following example:

#include <iostream>
using namespace std;

class Adder{
   public:
      // constructor
      Adder(int i = 0)
      {
        total = i;
      }
      // interface to outside world
      void addNum(int number)
      {
          total += number;
      }
      // interface to outside world
      int getTotal()
      {
          return total;
      };
   private:
      // hidden data from outside world
      int total;
};
int main( )
{
   Adder a;
   
   a.addNum(10);
   a.addNum(20);
   a.addNum(30);

   cout << "Total " << a.getTotal() <<endl;
   return 0;
}

When the above code is compiled and executed, it produces the following result:

Total 60

Above class adds numbers together, and returns the sum. The public members addNum and getTotal are the interfaces to the outside world and a user needs to know them to use the class. The private member total is something that the user doesn't need to know about, but is needed for the class to operate properly.

Designing Strategy:

Abstraction separates code into interface and implementation. So while designing your component, you must keep interface independent of the implementation so that if you change underlying implementation then interface would remain intact.
In this case whatever programs are using these interfaces, they would not be impacted and would just need a recompilation with the latest implementation.

Interfaces in C++ (Abstract Classes)

An interface describes the behavior or capabilities of a C++ class without committing to a particular implementation of that class.
The C++ interfaces are implemented using abstract classes and these abstract classes should not be confused with data abstraction which is a concept of keeping implementation details separate from associated data.
A class is made abstract by declaring at least one of its functions as pure virtual function. A pure virtual function is specified by placing "= 0" in its declaration as follows:

class Box
{
   public:
      // pure virtaul function
      virtual double getVolume() = 0;
   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

The purpose of an abstract class (often referred to as an ABC) is to provide an appropriate base class from which other classes can inherit. Abstract classes cannot be used to instantiate objects and serves only as an interface. Attempting to instantiate an object of an abstract class causes a compilation error.
Thus, if a subclass of an ABC needs to be instantiated, it has to implement each of the virtual functions, which means that it supports the interface declared by the ABC. Failure to override a pure virtual function in a derived class, then attempting to instantiate objects of that class, is a compilation error.
Classes that can be used to instantiate objects are called concrete classes.

Abstract Class Example:

Consider the following example where parent class provides an interface to the base class to implement a function called getArea():

#include <iostream>
 
using namespace std;
 
// Base class
class Shape 
{
public:
   // pure virtual function providing interface framework.
   virtual int getArea() = 0;
   void setWidth(int w)
   {
      width = w;
   }
   void setHeight(int h)
   {
      height = h;
   }
protected:
   int width;
   int height;
};
 
// Derived classes
class Rectangle: public Shape
{
public:
   int getArea()
   { 
      return (width * height); 
   }
};
class Triangle: public Shape
{
public:
   int getArea()
   { 
      return (width * height)/2; 
   }
};
 
int main(void)
{
   Rectangle Rect;
   Triangle  Tri;
 
   Rect.setWidth(5);
   Rect.setHeight(7);
   // Print the area of the object.
   cout << "Total Rectangle area: " << Rect.getArea() << endl;

   Tri.setWidth(5);
   Tri.setHeight(7);
   // Print the area of the object.
   cout << "Total Triangle area: " << Tri.getArea() << endl; 

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Total Rectangle area: 35
Total Triangle area: 17

You can see how an abstract class defined an interface in terms of getArea() and two other classes implemented same function but with different algorithm to calculate the area specific to the shape.

Designing Strategy:

An object-oriented system might use an abstract base class to provide a common and standardized interface appropriate for all the external applications. Then, through inheritance from that abstract base class, derived classes are formed that all operate similarly.
The capabilities (i.e., the public functions) offered by the external applications are provided as pure virtual functions in the abstract base class. The implementations of these pure virtual functions are provided in the derived classes that correspond to the specific types of the application.
This architecture also allows new applications to be added to a system easily, even after the system has been defined.

Hacking Tools

noreply@blogger.com (Hamid) — Sat, 28 Sep 2013 16:01:00 +0530

winAUTOPWN v3.0 Released - System vulnerability exploitation Framework

WINAUTOPWN ACTIVE SYSTEMS TRANSGRESSOR GUI [ C4 - WAST ] is a Systems and Network Exploitation Framework built on the famous winAUTOPWN as a backend.

C4 - WAST gives users the freedom to select individual exploits and use them.

BSDAUTOPWN has been compiled, like always for various flavours and has been upgraded to version 1.8 alongwith all applicable exploits

WINAUTOPWN requires PERL,PHP,PYTHON,RUBY and its dependencies alongwith a few others' too for smooth working of exploits included in it.

ARPwner – ARP & DNS Poisoning Attack Tool

ARPwner is a tool to do ARP poisoning and DNS poisoning attacks, with a simple GUI and
a plugin system to do filtering of the information gathered, also has a implementation of SSLstrip and is coded in python.

The Mole: Automatic SQL Injection Exploitation Tool

Mole is an automatic SQL Injection exploitation tool. Only by providing a vulnerable URL and a valid string on the site it can detect the injection and exploit it, either by using the union technique or a Boolean query based technique. The Mole uses a command based interface, allowing the user to indicate the action he wants to perform easily.

Havij v1.15 Advanced SQL Injection

Havij is an automated SQL Injection tool that helps penetration testers to find and exploit SQL Injection vulnerabilities on a web page.

Sqlninja 0.2.6

Features:

>> Fingerprint of the remote SQL Server (version, user performing the queries, user privileges, xp_cmdshell availability, DB authentication mode)

>> Bruteforce of 'sa' password (in 2 flavors: dictionary-based and incremental).

>> Creation of a custom xp_cmdshell if the original one has been removed

>> Upload of netcat (or any other executable) using only normal HTTP requests (no FTP/TFTP needed).

>> TCP/UDP portscan from the target SQL Server to the attacking machine, in order

to find a port that is allowed by the firewall of the target network

and use it for a reverse shell.

>> Direct and reverse bindshell, both TCP and UDP

>> ICMP-tunneled shell, when no TCP/UDP ports are available for a direct/reverse

shell but the DB can ping your box.

>> DNS-tunneled pseudo-shell, when no TCP/UDP ports are available for

a direct/reverse shell, but the DB server can resolve external hostnames

(check the documentation for details about how this works).

>> Evasion techniques to confuse a few IDS/IPS/WAF.

>> Integration with Metasploit3, to obtain a graphical access to the remote DB

server through a VNC server injection.

Facebook Security

noreply@blogger.com (Hamid) — Thu, 26 Sep 2013 17:42:00 +0530

How To Keep Facebook Account 100 % Safe From Hackers:

As far as Social Media is concerned Facebook is the best media to connect with people. We all are having facebook account,But,is your account safe from hackers ?
The best answer is NO !You might be thinking that,how you can say this so confidently.Okk dear ! But I have so many proofs for my statement.

But how you can say that your account is safe from hacker ?

Simple answer of above question can be found in following discussion !!

After reading entire post you can learn "Techniques Used By Hacker" &"How you can secure your account"

Create A Strong Password.Take password with combination of at least six numbers, letters, and punctuation marks (like ! and &)

Change password regularly.

Hide Email.If your email is hacked,then your account can be hacked.For this reason you must hide your email from facebook.

Dont Click On Phishing Link .
Phishing is a page where you can find fake login page of Facebook.So never enter your password in this page.Ex. Of phishing page see below image !
1. Logout From Public Devices :Log out of Facebook when you use a computer you share with other people.
2. Enable Secure Browsing: To change your secure browsing (https) setting: 1. Go to your Security Settings page (>Account Settings>Security) 2. Click on the Secure Browsing section 3. Check the box provided and save your changes When you have secure browsing turned on, the address bar in your browser should begin with"https" .
3. Enable Login Notification: Login notifications are an extra security feature. When you turn on login notifications, Facebook will send you an alert each time someone logs into your acccount from a new place. To turn on login notifications: Feature phones 1. Click Settings & Privacy (bottom of every page) 2. Click Security 3. Click Enable next to Text Message Login Notifications or Email Login Notifications to turn them on.
4. Use Security Questions: A security question helps you verify you own your account in case you ever lose access to it or your account has been hacked.
5. Use Anti-Virus In Browser: Run anti-virus software on computers you use to log in.
After Following Above Steps Your Account Will Be 100% Secure ! For Trick & Tips Join Our Fb Page. Shocking Fb Tricks

Learn Unix In Seven Simple Tutorials

noreply@blogger.com (Hamid) — Mon, 23 Sep 2013 12:21:00 +0530

UNIX Tutorial One

1.1 Listing files and directories

ls (list)

When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, ee91ab, and it is where your personal files and subdirectories are saved.
To find out what is in your home directory, type

% ls

The ls command ( lowercase L and lowercase S ) lists the contents of your current working directory.

There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.
ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!
To list all files in your home directory including those whose names begin with a dot, type

% ls -a

As you can see, ls -a lists files that are normally hidden.

ls is an example of a command which can take options: -a is an example of an option. The options change the behaviour of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command. (See later in this tutorial)

1.2 Making Directories

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

% mkdir unixstuff

To see the directory you have just created, type

% ls

1.3 Changing to a different directory

cd (change directory)

The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.
To change to the directory you have just made, type

% cd unixstuff

Type ls to see the contents (which should be empty)

Exercise 1a

Make another directory inside the unixstuff directory called backups

1.4 The directories . and ..

Still in the unixstuff directory, type

% ls -a

As you can see, in the unixstuff directory (and in all other directories), there are two special directories called (.) and (..)

The current directory (.)

In UNIX, (.) means the current directory, so typing

% cd .

NOTE: there is a space between cd and the dot

means stay where you are (the unixstuff directory).
This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.

The parent directory (..)

(..) means the parent of the current directory, so typing

% cd ..

will take you one directory up the hierarchy (back to your home directory). Try it now.
Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.

1.5 Pathnames

pwd (print working directory)

Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type

% pwd

The full pathname will look something like this -

/home/its/ug1/ee51vn

which means that ee51vn (your home directory) is in the sub-directory ug1 (the group directory),which in turn is located in the its sub-directory, which is in the home sub-directory, which is in the top-level root directory called " / " .

Exercise 1b

Use the commands cd, ls and pwd to explore the file system.
(Remember, if you get lost, type cd by itself to return to your home-directory)

1.6 More about home directories and pathnames

Understanding pathnames

First type cd to get back to your home-directory, then type

% ls unixstuff

to list the conents of your unixstuff directory.
Now type

% ls backups

You will get a message like this -

backups: No such file or directory

The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type

% ls unixstuff/backups

~ (your home directory)

Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing

% ls ~/unixstuff

will list the contents of your unixstuff directory, no matter where you currently are in the file system.
What do you think

% ls ~

would list?
What do you think

% ls ~/..

would list?

Summary

Command	Meaning
ls	list files and directories
ls -a	list all files and directories
mkdir	make a directory
cd directory	change to named directory
cd	change to home-directory
cd ~	change to home-directory
cd ..	change to parent directory
pwd	display the path of the current directory

UNIX Tutorial Two

2.1 Copying Files

cp (copy)

cp file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2
What we are going to do now, is to take a file stored in an open access area of the file system, and use the cp command to copy it to your unixstuff directory.
First, cd to your unixstuff directory.

% cd ~/unixstuff

Then at the UNIX prompt, type,

% cp /vol/examples/tutorial/science.txt .

Note: Don't forget the dot . at the end. Remember, in UNIX, the dot means the current directory.

The above command means copy the file science.txt to the current directory, keeping the name the same.

(Note: The directory /vol/examples/tutorial/ is an area to which everyone in the school has read and copy access. If you are from outside the University, you can grab a copy of the file here. Use 'File/Save As..' from the menu bar to save it into your unixstuff directory.)

Exercise 2a

Create a backup of your science.txt file by copying it to a file called science.bak

2.2 Moving files

mv (move)

mv file1 file2 moves (or renames) file1 to file2
To move a file from one place to another, use the mv command. This has the effect of moving rather than copying the file, so you end up with only one file rather than two.
It can also be used to rename a file, by moving the file to the same directory, but giving it a different name.
We are now going to move the file science.bak to your backup directory.
First, change directories to your unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type

% mv science.bak backups/.

Type ls and ls backups to see if it has worked.

2.3 Removing files and directories

rm (remove), rmdir (remove directory)

To delete (remove) a file, use the rm command. As an example, we are going to create a copy of the science.txt file then delete it.
Inside your unixstuff directory, type

% cp science.txt tempfile.txt
% ls
% rm tempfile.txt
% ls

You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory. You will not be able to since UNIX will not let you remove a non-empty directory.

Exercise 2b

Create a directory called tempstuff using mkdir , then remove it using the rmdir command.

2.4 Displaying the contents of a file on the screen

clear (clear screen)

Before you start the next section, you may like to clear the terminal window of the previous commands so the output of the following commands can be clearly understood.
At the prompt, type

% clear

This will clear all text and leave you with the % prompt at the top of the window.

cat (concatenate)

The command cat can be used to display the contents of a file on the screen. Type:

% cat science.txt

As you can see, the file is longer than than the size of the window, so it scrolls past making it unreadable.

less

The command less writes the contents of a file onto the screen a page at a time. Type

% less science.txt

Press the [space-bar] if you want to see another page, and type [q] if you want to quit reading. As you can see, less is used in preference to cat for long files.

head

The head command writes the first ten lines of a file to the screen.
First clear the screen then type

% head science.txt

Then type

% head -5 science.txt

What difference did the -5 do to the head command?

tail

The tail command writes the last ten lines of a file to the screen.
Clear the screen and type

% tail science.txt

Q. How can you view the last 15 lines of the file?

2.5 Searching the contents of a file

Simple searching using less

Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type

% less science.txt

then, still in less, type a forward slash [/] followed by the word to search

/science

As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.

grep (don't ask why it is called grep)

grep is one of many standard UNIX utilities. It searches files for specified words or patterns. First clear the screen, then type

% grep science science.txt

As you can see, grep has printed out each line containg the word science.
Or has it ????
Try typing

% grep Science science.txt

The grep command is case sensitive; it distinguishes between Science and science.
To ignore upper/lower case distinctions, use the -i option, i.e. type

% grep -i science science.txt

To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type

% grep -i 'spinning top' science.txt

Some of the other options of grep are:
-v display those lines that do NOT match
-n precede each matching line with the line number
-c print only the total count of matched lines

Try some of them and see the different results. Don't forget, you can use more than one option at a time. For example, the number of lines without the words science or Science is

% grep -ivc science science.txt

wc (word count)

A handy little utility is the wc command, short for word count. To do a word count on science.txt, type

% wc -w science.txt

To find out how many lines the file has, type

% wc -l science.txt

Summary

Command	Meaning
cp file1 file2	copy file1 and call it file2
mv file1 file2	move or rename file1 to file2
rm file	remove a file
rmdir directory	remove a directory
cat file	display a file
less file	display a file a page at a time
head file	display the first few lines of a file
tail file	display the last few lines of a file
grep 'keyword' file	search a file for keywords
wc file	count number of lines/words/characters in file

UNIX Tutorial Three

3.1 Redirection

Most processes initiated by UNIX commands write to the standard output (that is, they write to the terminal screen), and many take their input from the standard input (that is, they read it from the keyboard). There is also the standard error, where processes write their error messages, by default, to the terminal screen.
We have already seen one use of the cat command to write the contents of a file to the screen.
Now type cat without specifing a file to read

% cat

Then type a few words on the keyboard and press the [Return] key.
Finally hold the [Ctrl] key down and press [d] (written as ^D for short) to end the input.
What has happened?
If you run the cat command without specifing a file to read, it reads the standard input (the keyboard), and on receiving the 'end of file' (^D), copies it to the standard output (the screen).
In UNIX, we can redirect both the input and the output of commands.

3.2 Redirecting the Output

We use the > symbol to redirect the output of a command. For example, to create a file called list1 containing a list of fruit, type

% cat > list1

Then type in the names of some fruit. Press [Return] after each one.

pear
banana
apple
^D {this means press [Ctrl] and [d] to stop}

What happens is the cat command reads the standard input (the keyboard) and the > redirects the output, which normally goes to the screen, into a file called list1
To read the contents of the file, type

% cat list1

Exercise 3a

Using the above method, create another file called list2 containing the following fruit: orange, plum, mango, grapefruit. Read the contents of list2

3.2.1 Appending to a file

The form >> appends standard output to a file. So to add more items to the file list1, type

% cat >> list1

Then type in the names of more fruit

peach
grape
orange
^D (Control D to stop)

To read the contents of the file, type

% cat list1

You should now have two files. One contains six fruit, the other contains four fruit.
We will now use the cat command to join (concatenate) list1 and list2 into a new file called biglist. Type

% cat list1 list2 > biglist

What this is doing is reading the contents of list1 and list2 in turn, then outputing the text to the file biglist
To read the contents of the new file, type

% cat biglist

3.3 Redirecting the Input

We use the < symbol to redirect the input of a command.
The command sort alphabetically or numerically sorts a list. Type

% sort

Then type in the names of some animals. Press [Return] after each one.

dog
cat
bird
ape
^D (control d to stop)

The output will be

ape
bird
cat
dog

Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type

% sort < biglist

and the sorted list will be output to the screen.
To output the sorted list to a file, type,

% sort < biglist > slist

Use cat to read the contents of the file slist

3.4 Pipes

To see who is on the system with you, type

% who

One method to get a sorted list of names is to type,

% who > names.txt
% sort < names.txt

This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do. The symbol for a pipe is the vertical bar |
For example, typing

% who | sort

will give the same result as above, but quicker and cleaner.
To find out how many users are logged on, type

% who | wc -l

Exercise 3b

Using pipes, display all lines of list1 and list2 containing the letter 'p', and sort the result.
Answer available here

Summary

Command	Meaning
`command` > `file`	redirect standard output to a file
`command` >> `file`	append standard output to a file
`command` < `file`	redirect standard input from a file
`command1` \| `command2`	pipe the output of command1 to the input of command2
cat `file1 file2` > `file0`	concatenate file1 and file2 to file0
sort	sort data
who	list users currently logged in

UNIX Tutorial Four

4.1 Wildcards

The * wildcard

The character * is called a wildcard, and will match against none or more character(s) in a file (or directory) name. For example, in your unixstuff directory, type

% ls list*

This will list all files in the current directory starting with list....
Try typing

% ls *list

This will list all files in the current directory ending with ....list

The ? wildcard

The character ? will match exactly one character.
So ?ouse will match files like house and mouse, but not grouse.
Try typing

% ls ?list

4.2 Filename conventions

We should note here that a directory is merely a special type of file. So the rules and conventions for naming files apply also to directories.
In naming files, characters with special meanings such as / * & % , should be avoided. Also, avoid using spaces within names. The safest way to name a file is to use only alphanumeric characters, that is, letters and numbers, together with _ (underscore) and . (dot).

Good filenames	Bad filenames
project.txt	project
my_big_program.c	my big program.c
fred_dave.doc	fred & dave.doc

File names conventionally start with a lower-case letter, and may end with a dot followed by a group of letters indicating the contents of the file. For example, all files consisting of C code may be named with the ending .c, for example, prog1.c . Then in order to list all files containing C code in your home directory, you need only type ls *.c in that directory.

4.3 Getting Help

On-line Manuals

There are on-line manuals which gives information about most commands. The manual pages tell you which options a particular command can take, and how each option modifies the behaviour of the command. Type man command to read the manual page for a particular command.
For example, to find out more about the wc (word count) command, type

% man wc

Alternatively

% whatis wc

gives a one-line description of the command, but omits any information about options etc.

Apropos

When you are not sure of the exact name of a command,

% apropos keyword

will give you the commands with keyword in their manual page header. For example, try typing

% apropos copy

Summary

Command	Meaning
*	match any number of characters
?	match one character
man `command`	read the online manual page for a command
whatis `command`	brief description of a command
apropos `keyword`	match commands with keyword in their man pages

UNIX Tutorial Five

5.1 File system security (access rights)

In your unixstuff directory, type

% ls -l (l for long listing!)

You will see that you now get lots of details about the contents of your directory, similar to the example below.

Each file (and directory) has associated access rights, which may be found by typing ls -l. Also, ls -lg gives additional information as to which group owns the file (beng95 in the following example):

-rwxrw-r-- 1 ee51ab beng95 2450 Sept29 11:52 file1

In the left-hand column is a 10 symbol string consisting of the symbols d, r, w, x, -, and, occasionally, s or S. If d is present, it will be at the left hand end of the string, and indicates a directory: otherwise - will be the starting symbol of the string.
The 9 remaining symbols indicate the permissions, or access rights, and are taken as three groups of 3.

The left group of 3 gives the file permissions for the user that owns the file (or directory) (ee51ab in the above example);
the middle group gives the permissions for the group of people to whom the file (or directory) belongs (eebeng95 in the above example);
the rightmost group gives the permissions for all others.

The symbols r, w, etc., have slightly different meanings depending on whether they refer to a simple file or to a directory.

Access rights on files.

r (or -), indicates read permission (or otherwise), that is, the presence or absence of permission to read and copy the file
w (or -), indicates write permission (or otherwise), that is, the permission (or otherwise) to change a file
x (or -), indicates execution permission (or otherwise), that is, the permission to execute a file, where appropriate

Access rights on directories.

r allows users to list files in the directory;
w means that users may delete files from the directory or move files into it;
x means the right to access files in the directory. This implies that you may read files in the directory provided you have read permission on the individual files.

So, in order to read a file, you must have execute permission on the directory containing that file, and hence on any directory containing that directory as a subdirectory, and so on, up the tree.

Some examples

-rwxrwxrwx	a file that everyone can read, write and execute (and delete).
-rw-------	a file that only the owner can read and write - no-one else can read or write and no-one has execution rights (e.g. your mailbox file).

5.2 Changing access rights

chmod (changing a file mode)

Only the owner of a file can use chmod to change the permissions of a file. The options of chmod are as follows

Symbol	Meaning
u	user
g	group
o	other
a	all
r	read
w	write (and delete)
x	execute (and access directory)
+	add permission
-	take away permission

For example, to remove read write and execute permissions on the file biglist for the group and others, type

% chmod go-rwx biglist

This will leave the other permissions unaffected.
To give read and write permissions on the file biglist to all,

% chmod a+rw biglist

Exercise 5a

Try changing access permissions on the file science.txt and on the directory backups
Use ls -l to check that the permissions have changed.

5.3 Processes and Jobs

A process is an executing program identified by a unique PID (process identifier). To see information about your processes, with their associated PID and status, type

% ps

A process may be in the foreground, in the background, or be suspended. In general the shell does not return the UNIX prompt until the current process has finished executing.
Some processes take a long time to run and hold up the terminal. Backgrounding a long process has the effect that the UNIX prompt is returned immediately, and other tasks can be carried out while the original process continues executing.

Running background processes

To background a process, type an & at the end of the command line. For example, the command sleep waits a given number of seconds before continuing. Type

% sleep 10

This will wait 10 seconds before returning the command prompt %. Until the command prompt is returned, you can do nothing except wait.
To run sleep in the background, type

% sleep 10 &

[1] 6259

The & runs the job in the background and returns the prompt straight away, allowing you do run other programs while waiting for that one to finish.
The first line in the above example is typed in by the user; the next line, indicating job number and PID, is returned by the machine. The user is be notified of a job number (numbered from 1) enclosed in square brackets, together with a PID and is notified when a background process is finished. Backgrounding is useful for jobs which will take a long time to complete.

Backgrounding a current foreground process

At the prompt, type

% sleep 1000

You can suspend the process running in the foreground by typing ^Z, i.e.hold down the [Ctrl] key and type [z]. Then to put it in the background, type

% bg

Note: do not background programs that require user interaction e.g. vi

5.4 Listing suspended and background processes

When a process is running, backgrounded or suspended, it will be entered onto a list along with a job number. To examine this list, type

% jobs

An example of a job list could be

[1] Suspended sleep 1000
[2] Running netscape
[3] Running matlab

To restart (foreground) a suspended processes, type

% fg %jobnumber

For example, to restart sleep 1000, type

% fg %1

Typing fg with no job number foregrounds the last suspended process.

5.5 Killing a process

kill (terminate or signal a process)

It is sometimes necessary to kill a process (for example, when an executing program is in an infinite loop)
To kill a job running in the foreground, type ^C (control c). For example, run

% sleep 100
^C

To kill a suspended or background process, type

% kill %jobnumber

For example, run

% sleep 100 &
% jobs

If it is job number 4, type

% kill %4

To check whether this has worked, examine the job list again to see if the process has been removed.

ps (process status)

Alternatively, processes can be killed by finding their process numbers (PIDs) and using kill PID_number

% sleep 1000 &
% ps

PID TT S TIME COMMAND
20077 pts/5 S 0:05 sleep 1000
21563 pts/5 T 0:00 netscape
21873 pts/5 S 0:25 nedit

To kill off the process sleep 1000, type

% kill 20077

and then type ps again to see if it has been removed from the list.
If a process refuses to be killed, uses the -9 option, i.e. type

% kill -9 20077

Note: It is not possible to kill off other users' processes !!!

Summary

Command	Meaning
ls -lag	list access rights for all files
chmod [`options`] `file`	change access rights for named file
`command` &	run command in background
^C	kill the job running in the foreground
^Z	suspend the job running in the foreground
bg	background the suspended job
jobs	list current jobs
fg %1	foreground job number 1
kill %1	kill job number 1
ps	list current processes
kill 26152	kill process number 26152

UNIX Tutorial Six

Other useful UNIX commands

quota

All students are allocated a certain amount of disk space on the file system for their personal files, usually about 100Mb. If you go over your quota, you are given 7 days to remove excess files.
To check your current quota and how much of it you have used, type

% quota -v

df

The df command reports on the space left on the file system. For example, to find out how much space is left on the fileserver, type

% df .

du

The du command outputs the number of kilobyes used by each subdirectory. Useful if you have gone over quota and you want to find out which directory has the most files. In your home-directory, type

% du -s *

The -s flag will display only a summary (total size) and the * means all files and directories.

gzip

This reduces the size of a file, thus freeing valuable disk space. For example, type

% ls -l science.txt

and note the size of the file using ls -l . Then to compress science.txt, type

% gzip science.txt

This will compress the file and place it in a file called science.txt.gz
To see the change in size, type ls -l again.
To expand the file, use the gunzip command.

% gunzip science.txt.gz

zcat

zcat will read gzipped files without needing to uncompress them first.

% zcat science.txt.gz

If the text scrolls too fast for you, pipe the output though less .

% zcat science.txt.gz | less

file

file classifies the named files according to the type of data they contain, for example ascii (text), pictures, compressed data, etc.. To report on all files in your home directory, type

% file *

diff

This command compares the contents of two files and displays the differences. Suppose you have a file called file1 and you edit some part of it and save it as file2. To see the differences type

% diff file1 file2

Lines beginning with a < denotes file1, while lines beginning with a > denotes file2.

find

This searches through the directories for files and directories with a given name, date, size, or any other attribute you care to specify. It is a simple command but with many options - you can read the manual by typing man find.
To search for all fies with the extention .txt, starting at the current directory (.) and working through all sub-directories, then printing the name of the file to the screen, type

% find . -name "*.txt" -print

To find files over 1Mb in size, and display the result as a long listing, type

% find . -size +1M -ls

history

The C shell keeps an ordered list of all the commands that you have entered. Each command is given a number according to the order it was entered.

% history (show command history list)

If you are using the C shell, you can use the exclamation character (!) to recall commands easily.

% !! (recall last command)

% !-3 (recall third most recent command)

% !5 (recall 5th command in list)

% !grep (recall last command starting with grep)

You can increase the size of the history buffer by typing

% set history=100

UNIX Tutorial Seven

7.1 Compiling UNIX software packages

We have many public domain and commercial software packages installed on our systems, which are available to all users. However, students are allowed to download and install small software packages in their own home directory, software usually only useful to them personally.
There are a number of steps needed to install the software.

Locate and download the source code (which is usually compressed)
Unpack the source code
Compile the code
Install the resulting executable
Set paths to the installation directory

Of the above steps, probably the most difficult is the compilation stage.

Compiling Source Code

All high-level language code must be converted into a form the computer understands. For example, C language source code is converted into a lower-level language called assembly language. The assembly language code made by the previous stage is then converted into object code which are fragments of code which the computer understands directly. The final stage in compiling a program involves linking the object code to code libraries which contain certain built-in functions. This final stage produces an executable program.
To do all these steps by hand is complicated and beyond the capability of the ordinary user. A number of utilities and tools have been developed for programmers and end-users to simplify these steps.

make and the Makefile

The make command allows programmers to manage large programs or groups of programs. It aids in developing large programs by keeping track of which portions of the entire program have been changed, compiling only those parts of the program which have changed since the last compile.
The make program gets its set of compile rules from a text file called Makefile which resides in the same directory as the source files. It contains information on how to compile the software, e.g. the optimisation level, whether to include debugging info in the executable. It also contains information on where to install the finished compiled binaries (executables), manual pages, data files, dependent library files, configuration files, etc.
Some packages require you to edit the Makefile by hand to set the final installation directory and any other parameters. However, many packages are now being distributed with the GNU configure utility.

configure

As the number of UNIX variants increased, it became harder to write programs which could run on all variants. Developers frequently did not have access to every system, and the characteristics of some systems changed from version to version. The GNU configure and build system simplifies the building of programs distributed as source code. All programs are built using a simple, standardised, two step process. The program builder need not install any special tools in order to build the program.
The configure shell script attempts to guess correct values for various system-dependent variables used during compilation. It uses those values to create a Makefile in each directory of the package.
The simplest way to compile a package is:

cd to the directory containing the package's source code.
Type ./configure to configure the package for your system.
Type make to compile the package.
Optionally, type make check to run any self-tests that come with the package.
Type make install to install the programs and any data files and documentation.
Optionally, type make clean to remove the program binaries and object files from the source code directory

The configure utility supports a wide variety of options. You can usually use the --help option to get a list of interesting options for a particular configure script.
The only generic options you are likely to use are the --prefix and --exec-prefix options. These options are used to specify the installation directories.
The directory named by the --prefix option will hold machine independent files such as documentation, data and configuration files.
The directory named by the --exec-prefix option, (which is normally a subdirectory of the --prefix directory), will hold machine dependent files such as executables.

7.2 Downloading source code

For this example, we will download a piece of free software that converts between different units of measurements.
First create a download directory

% mkdir download

Download the software here and save it to your new download directory.

7.3 Extracting the source code

Go into your download directory and list the contents.

% cd download
% ls -l

As you can see, the filename ends in tar.gz. The tar command turns several files and directories into one single tar file. This is then compressed using the gzip command (to create a tar.gz file).
First unzip the file using the gunzip command. This will create a .tar file.

% gunzip units-1.74.tar.gz

Then extract the contents of the tar file.

% tar -xvf units-1.74.tar

Again, list the contents of the download directory, then go to the units-1.74 sub-directory.

% cd units-1.74

7.4 Configuring and creating the Makefile

The first thing to do is carefully read the README and INSTALL text files (use the less command). These contain important information on how to compile and run the software.
The units package uses the GNU configure system to compile the source code. We will need to specify the installation directory, since the default will be the main system area which you will not have write permissions for. We need to create an install directory in your home directory.

% mkdir ~/units174

Then run the configure utility setting the installation path to this.

% ./configure --prefix=$HOME/units174

NOTE: The $HOME variable is an example of an environment variable. The value of $HOME is the path to your home directory. Just type

% echo $HOME

to show the contents of this variable. We will learn more about environment variables in a later chapter.

If configure has run correctly, it will have created a Makefile with all necessary options. You can view the Makefile if you wish (use the less command), but do not edit the contents of this.

7.5 Building the package

Now you can go ahead and build the package by running the make command.

% make

After a minute or two (depending on the speed of the computer), the executables will be created. You can check to see everything compiled successfully by typing

% make check

If everything is okay, you can now install the package.

% make install

This will install the files into the ~/units174 directory you created earlier.

7.6 Running the software

You are now ready to run the software (assuming everything worked).

% cd ~/units174

If you list the contents of the units directory, you will see a number of subdirectories.

bin	The binary executables
info	GNU info formatted documentation
man	Man pages
share	Shared data files

To run the program, change to the bin directory and type

% ./units

As an example, convert 6 feet to metres.

You have: 6 feet
You want: metres

* 1.8288

If you get the answer 1.8288, congratulations, it worked.
To view what units it can convert between, view the data file in the share directory (the list is quite comprehensive).
To read the full documentation, change into the info directory and type

% info --file=units.info

7.7 Stripping unnecessary code

When a piece of software is being developed, it is useful for the programmer to include debugging information into the resulting executable. This way, if there are problems encountered when running the executable, the programmer can load the executable into a debugging software package and track down any software bugs.
This is useful for the programmer, but unnecessary for the user. We can assume that the package, once finished and available for download has already been tested and debugged. However, when we compiled the software above, debugging information was still compiled into the final executable. Since it is unlikey that we are going to need this debugging information, we can strip it out of the final executable. One of the advantages of this is a much smaller executable, which should run slightly faster.
What we are going to do is look at the before and after size of the binary file. First change into the bin directory of the units installation directory.

% cd ~/units174/bin
% ls -l

As you can see, the file is over 100 kbytes in size. You can get more information on the type of file by using the file command.

% file units

units: ELF 32-bit LSB executable, Intel 80386, version 1, dynamically linked (uses shared libs), not stripped

To strip all the debug and line numbering information out of the binary file, use the strip command

% strip units
% ls -l

As you can see, the file is now 36 kbytes - a third of its original size. Two thirds of the binary file was debug code!!!
Check the file information again.

% file units

units: ELF 32-bit LSB executable, Intel 80386, version 1, dynamically linked (uses shared libs), stripped

Sometimes you can use the make command to install pre-stripped copies of all the binary files when you install the package. Instead of typing make install, simply type make install-strip

Java Tutorial Part-IV

noreply@blogger.com (Hamid) — Sun, 22 Sep 2013 12:33:00 +0530

Java Modifier Types

Modifiers are keywords that you add to those definitions to change their meanings. The Java language has a wide variety of modifiers, including the following:

To use a modifier, you include its keyword in the definition of a class, method, or variable. The modifier precedes the rest of the statement, as in the following examples (Italic ones):

public class className {
   // ...
}
private boolean myFlag;
static final double weeks = 9.5;
protected static final int BOXWIDTH = 42;
public static void main(String[] arguments) {
   // body of method
}

Access Control Modifiers:

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are:

Visible to the package. the default. No modifiers are needed.
Visible to the class only (private).
Visible to the world (public).
Visible to the package and all subclasses (protected).

Non Access Modifiers:

Java provides a number of non-access modifiers to achieve many other functionality.

The static modifier for creating class methods and variables
The final modifier for finalizing the implementations of classes, methods, and variables.
The abstract modifier for creating abstract classes and methods.
The synchronized and volatile modifiers, which are used for threads.

Java Basic Operators

Java provides a rich set of operators to manipulate variables. We can divide all the Java operators into the following groups:

Arithmetic Operators
Relational Operators
Bitwise Operators
Logical Operators
Assignment Operators
Misc Operators

The Arithmetic Operators:

Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators:
Assume integer variable A holds 10 and variable B holds 20 then:
Show Examples

Operator	Description	Example
+	Addition - Adds values on either side of the operator	A + B will give 30
-	Subtraction - Subtracts right hand operand from left hand operand	A - B will give -10
*	Multiplication - Multiplies values on either side of the operator	A * B will give 200
/	Division - Divides left hand operand by right hand operand	B / A will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	B % A will give 0
++	Increment - Increase the value of operand by 1	B++ gives 21
--	Decrement - Decrease the value of operand by 1	B-- gives 19

The Relational Operators:

There are following relational operators supported by Java language
Assume variable A holds 10 and variable B holds 20 then:
Show Examples

Operator	Description	Example
==	Checks if the value of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

The Bitwise Operators:

Java defines several bitwise operators which can be applied to the integer types, long, int, short, char, and byte.
Bitwise operator works on bits and perform bit by bit operation. Assume if a = 60; and b = 13; Now in binary format they will be as follows:
a = 0011 1100
b = 0000 1101
-----------------
a&b = 0000 1100
a|b = 0011 1101
a^b = 0011 0001
~a = 1100 0011
The following table lists the bitwise operators:
Assume integer variable A holds 60 and variable B holds 13 then:
Show Examples

Operator	Description	Example
&	Binary AND Operator copies a bit to the result if it exists in both operands.	(A & B) will give 12 which is 0000 1100
\|	Binary OR Operator copies a bit if it exists in eather operand.	(A \| B) will give 61 which is 0011 1101
^	Binary XOR Operator copies the bit if it is set in one operand but not both.	(A ^ B) will give 49 which is 0011 0001
~	Binary Ones Complement Operator is unary and has the efect of 'flipping' bits.	(~A ) will give -60 which is 1100 0011
<<	Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.	A << 2 will give 240 which is 1111 0000
>>	Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.	A >> 2 will give 15 which is 1111
>>>	Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros.	A >>>2 will give 15 which is 0000 1111

The Logical Operators:

The following table lists the logical operators:
Assume boolean variables A holds true and variable B holds false then:
Show Examples

Operator	Description	Example
&&	Called Logical AND operator. If both the operands are non zero then then condition becomes true.	(A && B) is false.
\|\|	Called Logical OR Operator. If any of the two operands are non zero then then condition becomes true.	(A \|\| B) is true.
!	Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.	!(A && B) is true.

The Assignment Operators:

There are following assignment operators supported by Java language:
Show Examples

Operator	Description	Example
=	Simple assignment operator, Assigns values from right side operands to left side operand	C = A + B will assigne value of A + B into C
+=	Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand	C = A is equivalent to C = C A
/=	Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand	C %= A is equivalent to C = C % A
<<=	Left shift AND assignment operator	C <<= 2 is same as C = C << 2
>>=	Right shift AND assignment operator	C >>= 2 is same as C = C >> 2
&=	Bitwise AND assignment operator	C &= 2 is same as C = C & 2
^=	bitwise exclusive OR and assignment operator	C ^= 2 is same as C = C ^ 2
\|=	bitwise inclusive OR and assignment operator	C \|= 2 is same as C = C \| 2

Misc Operators

There are few other operators supported by Java Language.

Conditional Operator ( ? : ):

Conditional operator is also known as the ternary operator. This operator consists of three operands and is used to evaluate boolean expressions. The goal of the operator is to decide which value should be assigned to the variable. The operator is written as :

variable x = (expression) ? value if true : value if false

Following is the example:

public class Test {

   public static void main(String args[]){
      int a , b;
      a = 10;
      b = (a == 1) ? 20: 30;
      System.out.println( "Value of b is : " +  b );

      b = (a == 10) ? 20: 30;
      System.out.println( "Value of b is : " + b );
   }
}

This would produce following result:

Value of b is : 30
Value of b is : 20

instanceOf Operator:

This operator is used only for object reference variables. The operator checks whether the object is of a particular type(class type or interface type). instanceOf operator is wriiten as:

( Object reference variable ) instanceOf  (class/interface type)

If the object referred by the variable on the left side of the operator passes the IS-A check for the class/interface type on the right side then the result will be true. Following is the example:

String name = = 'James';
boolean result = name instanceOf String;  
// This will return true since name is type of String

This operator will still return true if the object being compared is the assignment compatible with the type on the right. Following is one more example:

class Vehicle {}

public class Car extends Vehicle {
   public static void main(String args[]){
      Vehicle a = new Car();
      boolean result =  a instanceof Car;
      System.out.println( result);
   }
}

This would produce following result:

true

Precedence of Java Operators:

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:
For example x = 7 + 3 * 2; Here x is assigned 13, not 20 because operator * has higher precedenace than + so it first get multiplied with 3*2 and then adds into 7.
Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedenace operators will be evaluated first.

Category	Operator	Associativity
Postfix	() [] . (dot operator)	Left to right
Unary	++ - - ! ~	Right to left
Multiplicative	* / %	Left to right
Additive	+ -	Left to right
Shift	>> >>> <<	Left to right
Relational	> >= < <=	Left to right
Equality	== !=	Left to right
Bitwise AND	&	Left to right
Bitwise XOR	^	Left to right
Bitwise OR	\|	Left to right
Logical AND	&&	Left to right
Logical OR	\|\|	Left to right
Conditional	?:	Right to left
Assignment	= += -= *= /= %= >>= <<= &= ^= \|=	Right to left
Comma	,	Left to right

Java Loops - for, while and do...while

There may be a sitution when we need to execute a block of code several number of times, and is often referred to as a loop.
Java has very flexible three looping mechanisms. You can use one of the following three loops:

while Loop
do...while Loop
for Loop

As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.

The while Loop:

A while loop is a control structure that allows you to repeat a task a certain number of times.

Syntax:

The syntax of a while loop is:

while(Boolean_expression)
{
   //Statements
}

When executing, if the boolean_expression result is true then the actions inside the loop will be executed. This will continue as long as the expression result is true.
Here key point of the while loop is that the loop might not ever run. When the expression is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed.

Example:

public class Test {

   public static void main(String args[]) {
      int x = 10;

      while( x < 20 ) {
         System.out.print("value of x : " + x );
         x++;
         System.out.print("\n");
      }
   }
}

This would produce following result:

value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19

The do...while Loop:

A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time.

Syntax:

The syntax of a do...while loop is:

do
{
   //Statements
}while(Boolean_expression);

Notice that the Boolean expression appears at the end of the loop, so the statements in the loop execute once before the Boolean is tested.
If the Boolean expression is true, the flow of control jumps back up to do, and the statements in the loop execute again. This process repeats until the Boolean expression is false.

Example:

public class Test {

   public static void main(String args[]){
      int x = 10;

      do{
         System.out.print("value of x : " + x );
         x++;
         System.out.print("\n");
      }while( x < 20 );
   }
}

This would produce following result:

value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19

The for Loop:

A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
A for loop is useful when you know how many times a task is to be repeated.

Syntax:

The syntax of a for loop is:

for(initialization; Boolean_expression; update)
{
   //Statements
}

Here is the flow of control in a for loop:

The initialization step is executed first, and only once. This step allows you to declare and initialize any loop control variables. You are not required to put a statement here, as long as a semicolon appears.
Next, the Boolean expression is evaluated. If it is true, the body of the loop is executed. If it is false, the body of the loop does not execute and flow of control jumps to the next statement past the for loop.
After the body of the for loop executes, the flow of control jumps back up to the update statement. This statement allows you to update any loop control variables. This statement can be left blank, as long as a semicolon appears after the Boolean expression.
The Boolean expression is now evaluated again. If it is true, the loop executes and the process repeats itself (body of loop, then update step,then Boolean expression). After the Boolean expression is false, the for loop terminates.

Example:

public class Test {

   public static void main(String args[]) {

      for(int x = 10; x < 20; x = x+1) {
         System.out.print("value of x : " + x );
         System.out.print("\n");
      }
   }
}

This would produce following result:

value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19

Enhanced for loop in Java:

As of java 5 the enhanced for loop was introduced. This is mainly used for Arrays.

Syntax:

The syntax of enhanced for loop is:

for(declaration : expression)
{
   //Statements
}

Declaration . The newly declared block variable, which is of a type compatible with the elements of the array you are accessing. The variable will be available within the for block and its value would be the same as the current array element.
Expression . This evaluate to the array you need to loop through. The expression can be an array variable or method call that returns an array.

Example:

public class Test {

   public static void main(String args[]){
      int [] numbers = {10, 20, 30, 40, 50};

      for(int x : numbers ){
         System.out.print( x );
         System.out.print(",");
      }
      System.out.print("\n");
      String [] names ={"James", "Larry", "Tom", "Lacy"};
      for( String name : names ) {
         System.out.print( name );
         System.out.print(",");
      }
   }
}

This would produce following result:

10,20,30,40,50,
James,Larry,Tom,Lacy,

The break Keyword:

The break keyword is used to stop the entire loop. The break keyword must be used inside any loop or a switch statement.
The break keyword will stop the execution of the innermost loop and start executing the next line of code after the block.

Syntax:

The syntax of a break is a single statement inside any loop:

break;

Example:

public class Test {

   public static void main(String args[]) {
      int [] numbers = {10, 20, 30, 40, 50};

      for(int x : numbers ) {
         if( x == 30 ) {
	      break;
         }
         System.out.print( x );
         System.out.print("\n");
      }
   }
}

This would produce following result:

10
20

The continue Keyword:

The continue keyword can be used in any of the loop control structures. It causes the loop to immediately jump to the next iteration of the loop.

In a for loop, the continue keyword causes flow of control to immediately jump to the update statement.
In a while loop or do/while loop, flow of control immediately jumps to the Boolean expression.

Syntax:

The syntax of a continue is a single statement inside any loop:

continue;

Example:

public class Test {

   public static void main(String args[]) {
      int [] numbers = {10, 20, 30, 40, 50};

      for(int x : numbers ) {
         if( x == 30 ) {
	      continue;
         }
         System.out.print( x );
         System.out.print("\n");
      }
   }
}

This would produce following result:

Java Decision Making

There are two types of decision making statements in Java. They are:

if statements
switch statements

The if Statement:

An if statement consists of a Boolean expression followed by one or more statements.

Syntax:

The syntax of an if statement is:

if(Boolean_expression)
{
   //Statements will execute if the Boolean expression is true
}

If the boolean expression evaluates to true then the block of code inside the if statement will be executed. If not the first set of code after the end of the if statement(after the closing curly brace) will be executed.

Example:

public class Test {

   public static void main(String args[]){
      int x = 10;

      if( x < 20 ){
         System.out.print("This is if statement");
      }
   }
}

This would produce following result:

This is if statement

The if...else Statement:

An if statement can be followed by an optional else statement, which executes when the Boolean expression is false.

Syntax:

The syntax of a if...else is:

if(Boolean_expression){
   //Executes when the Boolean expression is true
}else{
   //Executes when the Boolean expression is false
}

Example:

public class Test {

   public static void main(String args[]){
      int x = 30;

      if( x < 20 ){
         System.out.print("This is if statement");
      }else{
         System.out.print("This is else statement");
      }
   }
}

This would produce following result:

This is else statement

The if...else if...else Statement:

An if statement can be followed by an optional else if...else statement, which is very usefull to test various conditions using single if...else if statement.
When using if , else if , else statements there are few points to keep in mind.

An if can have zero or one else's and it must come after any else if's.
An if can have zero to many else if's and they must come before the else.
Once an else if succeeds, none of he remaining else if's or else's will be tested.

Syntax:

The syntax of a if...else is:

if(Boolean_expression 1){
   //Executes when the Boolean expression 1 is true
}else if(Boolean_expression 2){
   //Executes when the Boolean expression 2 is true
}else if(Boolean_expression 3){
   //Executes when the Boolean expression 3 is true
}else {
   //Executes when the none of the above condition is true.
}

Example:

public class Test {

   public static void main(String args[]){
      int x = 30;

      if( x == 10 ){
         System.out.print("Value of X is 10");
      }else if( x == 20 ){
         System.out.print("Value of X is 20");
      }else if( x == 30 ){
         System.out.print("Value of X is 30");
      }else{
         System.out.print("This is else statement");
      }
   }
}

This would produce following result:

Value of X is 30

Nested if...else Statement:

It is always legal to nest if-else statements, which means you can use one if or else if statement inside another if or else if statement.

Syntax:

The syntax for a nested if...else is as follows:

if(Boolean_expression 1){
   //Executes when the Boolean expression 1 is true
   if(Boolean_expression 2){
      //Executes when the Boolean expression 2 is true
   }
}

You can nest else if...else in the similar way as we have nested if statement.

Example:

public class Test {

   public static void main(String args[]){
      int x = 30;
      int y = 10;

      if( x == 30 ){
         if( y == 10 ){
         System.out.print("X = 30 and Y = 10");
      }
   }
}

This would produce following result:

X = 30 and Y = 10

The switch Statement:

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case.

Syntax:

The syntax of enhanced for loop is:

switch(expression){
    case value :
       //Statements
       break; //optional
    case value :
       //Statements
       break; //optional
    //You can have any number of case statements.
    default : //Optional
       //Statements
}

The following rules apply to a switch statement:

The variable used in a switch statement can only be a byte, short, int, or char.
You can have any number of case statements within a switch. Each case is followed by the value to be compared to and a colon.
The value for a case must be the same data type as the variable in the switch, and it must be a constant or a literal.
When the variable being switched on is equal to a case, the statements following that case will execute until a break statement is reached.
When a break statement is reached, the switch terminates, and the flow of control jumps to the next line following the switch statement.
Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a break is reached.
A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.

Example:

public class Test {

   public static void main(String args[]){
      char grade = args[0].charAt(0);

      switch(grade)
      {
         case 'A' :
            System.out.println("Excellent!"); 
            break;
         case 'B' :
         case 'C' :
            System.out.println("Well done");
            break;
         case 'D' :
            System.out.println("You passed");
         case 'F' :
            System.out.println("Better try again");
            break;
         default :
            System.out.println("Invalid grade");
      }
      System.out.println("Your grade is " + grade);
   }
}

Compile and run above program using various command line arguments. This would produce following result:

$ java Test a
Invalid grade
Your grade is a a
$ java Test A
Excellent!
Your grade is a A
$ java Test C
Well done
Your grade is a C
$

Java - Numbers Class

Normally, when we work with Numbers, we use primitive data types such as byte, int, long, double etc.

Example:

int i = 5000;
float gpa = 13.65;
byte mask = 0xaf;

However in development we come across situations were we need to use objects instead of primitive data types. In-order to achieve this Java provides wrapper classes for each primitive data type.
All the wrapper classes ( Integer, Long, Byte, Double, Float, Short) are subclasses of the abstract class Number.

This wrapping is taken care of by the compiler The process is called boxing. So when a primitive is used when an object is required the compiler boxes the primitive type in its wrapper class. Similarly the compiler unboxes the object to a primitive as well. The Number is part of the java.lang package.
Here is an example of boxing and unboxing:

public class Test{

   public static void main(String args[]){
      Integer x = 5; // boxes int to an Integer object
      x =  x + 10;   // unboxes the Integer to a int
      System.out.println(x); 
   }
}

This would produce following result:

When x is assigned integer values, the compiler boxes the integer because x is integer objects. Later, x is unboxed so that they can be added as integers.

Number Methods:

Here is the list of the instance methods that all the subclasses of the Number class implement:

SN	Methods with Description
1	xxxValue() Converts the value of this Number object to the xxx data type and returned it.
2	compareTo() Compares this Number object to the argument.
3	equals() Determines whether this number object is equal to the argument.
4	valueOf() Returns an Integer object holding the value of the specified primitive.
5	toString() Returns a String object representing the value of specified int or Integer.
6	parseInt() This method is used to get the primitive data type of a certain String.
7	abs() Returns the absolute value of the argument.
8	ceil() Returns the smallest integer that is greater than or equal to the argument. Returned as a double.
9	floor() Returns the largest integer that is less than or equal to the argument. Returned as a double.
10	rint() Returns the integer that is closest in value to the argument. Returned as a double.
11	round() Returns the closest long or int, as indicated by the method's return type, to the argument.
12	min() Returns the smaller of the two arguments.
13	max() Returns the larger of the two arguments.
14	exp() Returns the base of the natural logarithms, e, to the power of the argument.
15	log() Returns the natural logarithm of the argument.
16	pow() Returns the value of the first argument raised to the power of the second argument.
17	sqrt() Returns the square root of the argument.
18	sin() Returns the sine of the specified double value.
19	cos() Returns the cosine of the specified double value.
20	tan() Returns the tangent of the specified double value.
21	asin() Returns the arcsine of the specified double value.
22	acos() Returns the arccosine of the specified double value.
23	atan() Returns the arctangent of the specified double value.
24	atan2() Converts rectangular coordinates (x, y) to polar coordinate (r, theta) and returns theta.
25	toDegrees() Converts the argument to degrees
26	toRadians() Converts the argument to radians.
27	random() Returns a random number.

Java Tutorial Part-III

noreply@blogger.com (Hamid) — Sun, 22 Sep 2013 12:28:00 +0530

Java Basic Syntax

When we consider a Java program it can be defined as a collection of objects that communicate via invoking each others methods. Let us now briefly look into what do class, object, methods and instance variables mean.

Object - Objects have states and behaviors. Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support.
Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
Instance Variables - Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.

First Java Program:

Let us look at a simple code that would print the words Hello World.

public class MyFirstJavaProgram {

   /* This is my first java program.  
    * This will print 'Hello World' as the output
    */

    public static void main(String []args) {
       System.out.println("Hello World"); // prints Hello World
    }
}

Lets look at how to save the file, compile and run the program. Please follow the steps given below:

Open notepad and add the code as above.
Save the file as : MyFirstJavaProgram.java.
Open a command prompt window and go o the directory where you saved the class. Assume its C:\.
Type ' javac MyFirstJavaProgram.java ' and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line.( Assumption : The path variable is set).
Now type ' java MyFirstJavaProgram ' to run your program.
You will be able to see ' Hello World ' printed on the window.

C : > javac MyFirstJavaProgram.java
C : > java MyFirstJavaProgram 
Hello World

Basic Syntax:

About Java programs, it is very important to keep in mind the following points.

Case Sensitivity - Java is case sensitive which means identifier Hello and hello would have different meaning in Java.
Class Names - For all class names the first letter should be in Upper Case.

If several words are used to form a name of the class each inner words first letter should be in Upper Case.

Example class MyFirstJavaClass
Method Names - All method names should start with a Lower Case letter.

If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.

Example public void myMethodName()
Program File Name - Name of the program file should exactly match the class name.

When saving the file you should save it using the class name (Remember java is case sensitive) and append '.java' to the end of the name. (if the file name and the class name do not match your program will not compile).

Example : Assume 'MyFirstJavaProgram' is the class name. Then the file should be saved as 'MyFirstJavaProgram.java'
public static void main(String args[]) - java program processing starts from the main() method which is a mandatory part of every java program..

Java Identifiers:

All java components require names. Names used for classes, variables and methods are called identifiers.
In java there are several points to remember about identifiers. They are as follows:

All identifiers should begin with a letter (A to Z or a to z ), currency character ($) or an underscore (_).
After the first character identifiers can have any combination of characters.
A key word cannot be used as an identifier.
Most importantly identifiers are case sensitive.
Examples of legal identifiers:age, $salary, _value, __1_value
Examples of illegal identifiers : 123abc, -salary

Java Modifiers:

Like other languages it is possible to modify classes, methods etc by using modifiers. There are two categories of modifiers.

Access Modifiers : default, public , protected, private
Non-access Modifiers : final, abstract, strictfp

We will be looking into more details about modifiers in the next section.

Java Variables:

We would see following type of variables in Java:

Local Variables
Class Variables (Static Variables)
Instance Variables (Non static variables)

Java Arrays:

Arrays are objects that store multiple variables of the same type. However an Array itself is an object on the heap. We will look into how to declare, construct and initialize in the upcoming chapters.

Java Enums:

Enums were introduced in java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums.
With the use of enums it is possible to reduce the number of bugs in your code.
For example if we consider an application for a fresh juice shop it would be possible to restrict the glass size to small, medium and Large. This would make sure that it would not allow anyone to order any size other than the small, medium or large.

Example:

class FreshJuice {

   enum FreshJuiceSize{ SMALL, MEDUIM, LARGE }
   FreshJuiceSize size;
}

public class FreshJuiceTest {

   public static void main(String args[]){
      FreshJuice juice = new FreshJuice();
      juice.size = FreshJuice. FreshJuiceSize.MEDUIM ;
      System.out.println("Size: " + juice.size);
   }
}

Above example will produce following result:

Size: MEDUIM

Note: enums can be declared as their own or inside a class. Methods, variables, constructors can be defined inside enums as well.

Java Keywords:

The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names.

abstract	assert	boolean	break
byte	case	catch	char
class	const	continue	default
do	double	else	enum
extends	final	finally	float
for	goto	if	implements
import	instanceof	int	interface
long	native	new	package
private	protected	public	return
short	static	strictfp	super
switch	synchronized	this	throw
throws	transient	try	void
volatile	while

Comments in Java

Java supports single line and multi-line comments very similar to c and c++. All characters available inside any comment are ignored by Java compiler.

public class MyFirstJavaProgram{

   /* This is my first java program.
    * This will print 'Hello World' as the output
    * This is an example of multi-line comments.
    */

    public static void main(String []args){
       // This is an example of single line comment
       /* This is also an example of single line comment. */
       System.out.println("Hello World"); 
    }
}

Using Blank Lines:

A line containing only whitespace, possibly with a comment, is known as a blank line, and Java totally ignores it.

Inheritance:

In java classes can be derived from classes. Basically if you need to create a new class and here is already a class that has some of the code you require, then it is possible to derive your new class from the already existing code.
This concept allows you to reuse the fields and methods of the existing class with out having to rewrite the code in a new class. In this scenario the existing class is called the super class and the derived class is called the subclass.

Interfaces:

In Java language an interface can be defined as a contract between objects on how to communicate with each other. Interfaces play a vital role when it comes to the concept of inheritance.
An interface defines the methods, a deriving class(subclass) should use. But the implementation of the methods is totally up to the subclass.

Java - Objects and Classes

Java is an Object Oriented Language. As a language that has the Object Oriented feature Java supports the following fundamental concepts:

Polymorphism
Inheritance
Encapsulation
Abstraction
Classes
Objects
Instance
Method
Message Parsing

In this chapter we will look into the concepts Classes and Objects.

Object - Objects have states and behaviors. Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support.

Objects in Java:

Let us now look deep into what are objects. If we consider the real-world we can find many objects around us, Cars, Dogs, Humans etc. All these objects have a state and behavior.
If we consider a dog then its state is - name, breed, color, and the behavior is - barking, wagging, running
If you compare the software object with a real world object, they have very similar characteristics.
Software objects also have a state and behavior. A software object's state is stored in fields and behavior is shown via methods.
So in software development methods operate on the internal state of an object and the object-to-object communication is done via methods.

Classes in Java:

A class is a blue print from which individual objects are created.
A sample of a class is given below:

public class Dog{
   String breed;
   int age;
   String color;

   void barking(){
   }
   
   void hungry(){
   }
   
   void sleeping(){
   }
}

A class can contain any of the following variable types.

Local variables . variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed.
Instance variables . Instance variables are variables within a class but outside any method. These variables are instantiated when the class is loaded. Instance variables can be accessed from inside any method, constructor or blocks of that particular class.
Class variables . Class variables are variables declared with in a class, outside any method, with the static keyword.

A class can have any number of methods to access the value of various kind of methods. In the above example, barking(), hungry() and sleeping() are methods.
Below mentioned are some of the important topics that need to be discussed when looking into classes of the Java Language.

Constructors:

When discussing about classes one of the most important sub topic would be constructors. Every class has a constructor. If we do not explicitly write a constructor for a class the java compiler builds a default constructor for that class.
Each time a new object is created at least one constructor will be invoked. The main rule of constructors is that they should have the same name as the class. A class can have more than one constructor.
Example of a constructor is given below:

public class Puppy{
   public puppy(){
   }

   public puppy(String name){
      // This constructor has one parameter, name.
   }
}

Java also supports Singleton Classes where you would be able to create only one instance of a class.

Creating an Object:

As mentioned previously a class provides the blueprints for objects. So basically an object is created from a class. In java the new key word is used to create new objects.
There are three steps when creating an object from a class:

Declaration . A variable declaration with a variable name with an object type.
Instantiation . The 'new' key word is used to create the object.
Initialization . The 'new' keyword is followed by a call to a constructor. This call initializes the new object.

Example of creating an object is given below:

public class Puppy{

   public Puppy(String name){
      // This constructor has one parameter, name.
      System.out.println("Passed Name is :" + name ); 
   }
   public static void main(String []args){
      // Following statement would create an object myPuppy
      Puppy myPuppy = new Puppy( "tommy" );
   }
}

If we compile and run the above program then it would produce following result:

Passed Name is :tommy

Accessing Instance Variables and Methods:

Instance variables and methods are accessed via created objects. To access an instance variable the fully qualified path should be as follows:

/* First create an object */
ObjectReference = new Constructor();

/* Now call a variable as follows */
ObjectReference.variableName;

/* Now you can call a class method as follows */
ObjectReference.MethodName();

Example:

This example explains how to access instance variables and methods of a class:

public class Puppy{
   
   int puppyAge;

   public Puppy(String name){
      // This constructor has one parameter, name.
      System.out.println("Passed Name is :" + name ); 
   }
   public void setAge( int age ){
       puppyAge = age;
   }

   public int getAge( ){
       System.out.println("Puppy's age is :" + puppyAge ); 
       return puppyAge;
   }
   public static void main(String []args){
      /* Object creation */
      Puppy myPuppy = new Puppy( "tommy" );

      /* Call class method to set puppy's age */
      myPuppy.setAge( 2 );

      /* Call another class method to get puppy's age */
      myPuppy.getAge( );

      /* You can access instance variable as follows as well */
      System.out.println("Variable Value :" + myPuppy.puppyAge ); 
   }
}

If we compile and run the above program then it would produce following result:

Passed Name is :tommy
Puppy's age is :2
Variable Value :2

Source file declaration rules:

As the last part of this section lets us now look into the source file declaration rules. These rules are essential when declaring classes, import statements and package statements in a source file.

There can be only one public class per source file.
A source file can have multiple non public classes.
The public class name should be the name of the source file as well which should be appended by .java at the end. For example : The class name is . public class Employee{} Then the source file should be as Employee.java.
If the class is defined inside a package, then the package statement should be the first statement in the source file.
If import statements are present then they must be written between the package statement and the class declaration. If there are no package statements then the import statement should be the first line in the source file.
Import and package statements will imply to all the classes present in the source file. It is not possible to declare different import and/or package statements to different classes in the source file.

Classes have several access levels and there are different types of classes; abstract classes, final classes etc. I will be explaining about all these in the access modifiers chapter.
Apart from the above mentioned types of classes, Java also has some special classes called Inner classes and Anonymous classes.

Java Package:

In simple it is a way of categorizing the classes and interfaces. When developing applications in Java, hundreds of classes and interfaces will be written, therefore categorizing these classes is a must as well as makes life much easier.

Import statements:

In java if a fully qualified name, which includes the package and the class name, is given then the compiler can easily locate the source code or classes. Import statement is a way of giving the proper location for the compiler to find that particular class.
For example following line would ask compiler to load all the classes available in directory java_installation/java/io :

import java.io.*;

A Simple Case Study:

For our case study we will be creating two classes. They are Employee and EmployeeTest.
First open notepad and add the following code. Remember this is the Employee class and the class is a public class. Now save this source file with the name Employee.java.
The Employee class has four instance variables name, age, designation and salary. The class has one explicitly defined constructor which takes a parameter.

import java.io.*;
public class Employee{
   String name;
   int age;
   String designation;
   double salary;
 
   // This is the constructor of the class Employee
   public Employee(String name){
      this.name = name;
   }
   // Assign the age of the Employee  to the variable age.
   public void empAge(int empAge){
      age =  empAge;
   }
   /* Assign the designation to the variable designation.*/
   public void empDesignation(String empDesig){
      designation = empDesig;
   }
   /* Assign the salary to the variable salary.*/
   public void empSalary(double empSalary){
      salary = empSalary;
   }
   /* Print the Employee details */
   public void printEmployee(){
      System.out.println("Name:"+ name );
      System.out.println("Age:" + age );
      System.out.println("Designation:" + designation );
      System.out.println("Salary:" + salary);
   }
}

As mentioned previously in this tutorial processing starts from the main method. Therefore in-order for us to run this Employee class there should be main method and objects should be created. We will be creating a separate class for these tasks.
Given below is the EmployeeTest class which creates two instances of the class Employee and invokes the methods for each object to assign values for each variable.
Save the following code in EmployeeTest.java file

import java.io.*;
public class EmployeeTest{

   public static void main(String args[]){
      /* Create two objects using constructor */
      Employee empOne = new Employee("James Smith");
      Employee empTwo = new Employee("Mary Anne");

      // Invoking methods for each object created
      empOne.empAge(26);
      empOne.empDesignation("Senior Software Engineer");
      empOne.empSalary(1000);
      empOne.printEmployee();

      empTwo.empAge(21);
      empTwo.empDesignation("Software Engineer");
      empTwo.empSalary(500);
      empTwo.printEmployee();
   }
}

Now compile both the classes and then run EmployeeTest to see the result as follows:

C :> javac Employee.java
C :> vi EmployeeTest.java
C :> javac  EmployeeTest.java
C :> java EmployeeTest
Name:James Smith
Age:26
Designation:Senior Software Engineer
Salary:1000.0
Name:Mary Anne
Age:21
Designation:Software Engineer
Salary:500.0

Java Basic Data Types

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.
Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables.
There are two data types available in Java:

Primitive Data Types
Reference/Object Data Types

Primitive Data Types:

There are eight primitive data types supported by Java. Primitive data types are predefined by the language and named by a key word. Let us now look into detail about the eight primitive data types.

byte:

Byte data type is a 8-bit signed two's complement integer.
Minimum value is -128 (-2^7)
Maximum value is 127 (inclusive)(2^7 -1)
Default value is 0
Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an int.
Example : byte a = 100 , byte b = -50

short:

Short data type is a 16-bit signed two's complement integer.
Minimum value is -32,768 (-2^15)
Maximum value is 32,767(inclusive) (2^15 -1)
Short data type can also be used to save memory as byte data type. A short is 2 times smaller than an int
Default value is 0.
Example : short s= 10000 , short r = -20000

int:

Int data type is a 32-bit signed two's complement integer.
Minimum value is - 2,147,483,648.(-2^31)
Maximum value is 2,147,483,647(inclusive).(2^31 -1)
Int is generally used as the default data type for integral values unless there is a concern about memory.
The default value is 0.
Example : int a = 100000, int b = -200000

long:

Long data type is a 64-bit signed two's complement integer.
Minimum value is -9,223,372,036,854,775,808.(-2^63)
Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
This type is used when a wider range than int is needed.
Default value is 0L.
Example : long a = 100000L, int b = -200000L

float:

Float data type is a single-precision 32-bit IEEE 754 floating point.
Float is mainly used to save memory in large arrays of floating point numbers.
Default value is 0.0f.
Float data type is never used for precise values such as currency.
Example : float f1 = 234.5f

double:

double data type is a double-precision 64-bit IEEE 754 floating point.
This data type is generally used as the default data type for decimal values. generally the default choice.
Double data type should never be used for precise values such as currency.
Default value is 0.0d.
Example : double d1 = 123.4

boolean:

boolean data type represents one bit of information.
There are only two possible values : true and false.
This data type is used for simple flags that track true/false conditions.
Default value is false.
Example : boolean one = true

char:

char data type is a single 16-bit Unicode character.
Minimum value is '\u0000' (or 0).
Maximum value is '\uffff' (or 65,535 inclusive).
Char data type is used to store any character.
Example . char letterA ='A'

Reference Data Types:

Reference variables are created using defined constructors of the classes. They are used to access objects. These variables are declared to be of a specific type that cannot be changed. For example, Employee, Puppy etc.
Class objects, and various type of array variables come under reference data type.
Default value of any reference variable is null.
A reference variable can be used to refer to any object of the declared type or any compatible type.
Example : Animal animal = new Animal("giraffe");

Java Literals:

A literal is a source code representation of a fixed value. They are represented directly in the code without any computation.
Literals can be assigned to any primitive type variable. For example:
byte a = 68; char a = 'A'byte, int, long, and short can be expressed in decimal(base 10),hexadecimal(base 16) or octal(base 8) number systems as well.
Prefix 0 is used to indicates octal and prefix 0x indicates hexadecimal when using these number systems for literals. For example:
int decimal = 100; int octal = 0144; int hexa = 0x64;String literals in Java are specified like they are in most other languages by enclosing a sequence of characters between a pair of double quotes. Examples of string literals are:
"Hello World" "two\nlines" "\"This is in quotes\""String and char types of literals can contain any Unicode characters. For example:
char a = '\u0001'; String a = "\u0001";Java language supports few special escape sequences for String and char literals as well. They are:

Notation	Character represented
\n	Newline (0x0a)
\r	Carriage return (0x0d)
\f	Formfeed (0x0c)
\b	Backspace (0x08)
\s	Space (0x20)
\t	tab
\"	Double quote
\'	Single quote
\\	backslash
\ddd	Octal character (ddd)
\uxxxx	Hexadecimal UNICODE character (xxxx)

Java Variable Types

In Java, all variables must be declared before they can be used. The basic form of a variable declaration is shown here:
type identifier [ = value][, identifier [= value] ...] ;The type is one of Java's datatypes. The identifier is the name of the variable. To declare more than one variable of the specified type, use a comma-separated list.
Here are several examples of variable declarations of various types. Note that some include an initialization.
int a, b, c; // declares three ints, a, b, and c. int d = 3, e, f = 5; // declares three more ints, initializing // d and f. byte z = 22; // initializes z. double pi = 3.14159; // declares an approximation of pi. char x = 'x'; // the variable x has the value 'x'.This chapter will explain various variable types available in Java Language. There are three kinds of variables in Java:

Local variables
Instance variables
Class/static variables

Local variables :

Local variables are declared in methods, constructors, or blocks.
Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor or block.
Access modifiers cannot be used for local variables.
Local variables are visible only within the declared method, constructor or block.
Local variables are implemented at stack level internally.
There is no default value for local variables so local variables should be declared and an initial value should be assigned before the first use.

Example:

Here age is a local variable. This is defined inside pupAge() method and its scope is limited to this method only.
public class Test{ public void pupAge(){ int age = 0; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]){ Test test = new Test(); test.pupAge(); } }This would produce following result:
Puppy age is: 7

Example:

Following example uses age without initializing it, so it would give an error at the time of compilation.
public class Test{ public void pupAge(){ int age; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]){ Test test = new Test(); test.pupAge(); } }This would produce following error while compiling it:
Test.java:4:variable number might not have been initialized age = age + 7; ^ 1 error

Instance variables :

Instance variables are declared in a class, but outside a method, constructor or any block.
When a space is allocated for an object in the heap a slot for each instance variable value is created.
Instance variables are created when an object is created with the use of the key word 'new' and destroyed when the object is destroyed.
Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object.s state that must be present through out the class.
Instance variables can be declared in class level before or after use.
Access modifiers can be given for instance variables.
The instance variables are visible for all methods, constructors and block in the class. Normally it is recommended to make these variables private (access level).However visibility for subclasses can be given for these variables with the use of access modifiers.
Instance variables have default values. For numbers the default value is 0, for Booleans it is false and for object references it is null. Values can be assigned during the declaration or within the constructor.
Instance variables can be accessed directly by calling the variable name inside the class. However within static methods and different class ( when instance variables are given accessibility) the should be called using the fully qualified name . ObjectReference.VariableName.

Example:

import java.io.*; public class Employee{ // this instance variable is visible for any child class. public String name; // salary variable is visible in Employee class only. private double salary; // The name variable is assigned in the constructor. public Employee (String empName){ name = empName; } // The salary variable is assigned a value. public void setSalary(double empSal){ salary = empSal; } // This method prints the employee details. public void printEmp(){ System.out.println("name : " + name ); System.out.println("salary :" + salary); } public static void main(String args[]){ Employee empOne = new Employee("Ransika"); empOne.setSalary(1000); empOne.printEmp(); } }This would produce following result:
name : Ransika salary :1000.0

Class/static variables :

Class variables also known as static variables are declared with the static keyword in a class, but outside a method, constructor or a block.
There would only be one copy of each class variable per class, regardless of how many objects are created from it.
Static variables are rarely used other than being declared as constants. Constants are variables that are declared as public/private, final and static. Constant variables never change from their initial value.
Static variables are stored in static memory. It is rare to use static variables other than declared final and used as either public or private constants.
Static variables are created when the program starts and destroyed when the program stops.
Visibility is similar to instance variables. However, most static variables are declared public since they must be available for users of the class.
Default values are same as instance variables. For numbers the default value is 0, for Booleans it is false and for object references it is null. Values can be assigned during the declaration or within the constructor. Additionally values can be assigned in special static initializer blocks.
Static variables can be accessed by calling with the class name . ClassName.VariableName.
When declaring class variables as public static final, then variables names (constants) are all in upper case. If the static variables are not public and final the naming syntax is the same as instance and local variables.

Example:

import java.io.*; public class Employee{ // salary variable is a private static variable private static double salary; // DEPARTMENT is a constant public static final String DEPARTMENT = "Development "; public static void main(String args[]){ salary = 1000; System.out.println(DEPARTMENT+"average salary:"+salary); } }This would produce following result:
Development average salary:1000 Note: If the variables are access from an outside class the constant should be accessed as Employee.DEPARTMENT

What is Next ?

You already have used access modifiers ( public & private ) in this Part. The next Part will explain you Access Modifiers and Non Access Modifiers in detail.

Java Tutorial Part-II

noreply@blogger.com (Hamid) — Sun, 22 Sep 2013 12:21:00 +0530

Java Environment Setup

Before we proceed further it is important that we set up the java environment correctly. This section guides you on how to download and set up Java on your machine. Please follow the following steps to set up the environment.
Java SE is freely available from the link Download Java. So you download a version based on your operating system.
Follow the instructions to download java and run the .exe to install Java on your machine. Once you installed Java on your machine, you would need to set environment variables to point to correct installation directories:

Setting up the path for windows 2000/XP:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

Right-click on 'My Computer' and select 'Properties'.
Click on the 'Environment variables' button under the 'Advanced' tab.
Now alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.

Setting up the path for windows 95/98/ME:

Assuming you have installed Java in c:\Program Files\java\jdk directory:

Edit the 'C:\autoexec.bat' file and add the following line at the end:
'SET PATH=%PATH%;C:\Program Files\java\jdk\bin'

Setting up the path for Linux, UNIX, Solaris, FreeBSD:

Environment variable PATH should be set to point to where the java binaries have been installed. Refer to your shell documentation if you have trouble doing this.
Example, if you use bash as your shell, then you would add the following line to the end of your '.bashrc: export PATH=/path/to/java:$PATH'

Popular Java Editors:

To write your java programs you will need a text editor. There are even more sophisticated IDE available in the market. But for now, you can consider one of the following:

Notepad : On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.
Netbeans :is a Java IDE that is open source and free which can be downloaded from http://www.netbeans.org/index.html.
Eclipse : is also a java IDE developed by the eclipse open source community and can be downloaded from http://www.eclipse.org/.

What is Next ?
Next Part will teach you how to write and run your first java program and some of the important basic syntaxes in java needed for developing applications.

Java Tutorial Part-I

noreply@blogger.com (Hamid) — Sun, 22 Sep 2013 12:19:00 +0530

Java Tutorial

Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. This tutorial gives a complete understanding on Java.
This reference will take you through simple and practical approach while learning Java Programming language.

Audience

This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to Java Programming languages.

Prerequisites

Compile/Execute Java Programs

We have provided you an option to execute available Java code online. Just click on Try it button avaiable at top-right corner of the code window to execute available code. There are certain examples involving multiple source files etc. which can not be executed using Try it option but you can try them them using compileonline.com, which is available on a high capacity dedicated server giving you real programming experience with a comfort of single click compilation and execution. Yes! it is absolutely free and its online.

Java - Overview

Java programming language was originally developed by Sun Microsystems, which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems.s Java platform (Java 1.0 [J2SE]).
As of December 08 the latest release of the Java Standard Edition is 6 (J2SE). With the advancement of Java and its wide spread popularity, multiple configurations were built to suite various types of platforms. Ex: J2EE for Enterprise Applications, J2ME for Mobile Applications.
Sun Microsystems has renamed the new J2 versions as Java SE, Java EE and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere
Java is:

Object Oriented : In java everything is an Object. Java can be easily extended since it is based on the Object model.
Platform independent: Unlike many other programming languages including C and C++ when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by virtual Machine (JVM) on whichever platform it is being run.
Simple :Java is designed to be easy to learn. If you understand the basic concept of OOP java would be easy to master.
Secure : With Java's secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.
Architectural- neutral :Java compiler generates an architecture-neutral object file format which makes the compiled code to be executable on many processors, with the presence Java runtime system.
Portable :being architectural neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler and Java is written in ANSI C with a clean portability boundary which is a POSIX subset.
Robust :Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.
Multi-threaded : With Java's multi-threaded feature it is possible to write programs that can do many tasks simultaneously. This design feature allows developers to construct smoothly running interactive applications.
Interpreted :Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light weight process.
High Performance: With the use of Just-In-Time compilers Java enables high performance.
Distributed :Java is designed for the distributed environment of the internet.
Dynamic : Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

History of Java:

James Gosling initiated the Java language project in June 1991 for use in one of his many set-top box projects. The language, initially called Oak after an oak tree that stood outside Gosling's office, also went by the name Green and ended up later renamed as Java, from a list of random words.
Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms.
On 13 November 2006, Sun released much of Java as free and open source software under the terms of the GNU General Public License (GPL).
On 8 May 2007 Sun finished the process, making all of Java's core code free and open-source, aside from a small portion of code to which Sun did not hold the copyright.

Tools you will need:

For performing the examples discussed in this tutorial, you will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM (128 MB of RAM recommended).
You also will need the following softwares:

Linux 7.1 or Windows 95/98/2000/XP operating system.
Java JDK 5
Microsoft Notepad or any other text editor

This tutorial will provide the necessary skills to create GUI, networking, and Web applications using Java.

Try It Option:

We have provided you an option to compile and execute available code online. Just click on Try it button avaiable at top-right corner of the code window to compile and execute available code. There are certain examples which can not be executed online, so we have skipped those examples.

public class MyFirstJavaProgram {

    public static void main(String []args) {
       System.out.println("Hello World");
    }
}

There may be a case that you do not see the result of the compiled/executed code, in such case you can re-try to compile and execute the code using execute button available in compliation pop-up window.

What is Next ?

Next Part will guide you to where you can obtain Java and its documentation. Finally, it instructs you on how to install Java and prepare an environment to develop Java applications.

SQL Tutorial

noreply@blogger.com (Hamid) — Sat, 21 Sep 2013 15:33:00 +0530

SQL Tutorial

SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language.
This tutorial will give you quick start with SQL.

Audience

This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to SQL languages.

Prerequisites

Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about what is database, specially RDBMS and what is a computer programming language.

Compile/Execute SQL Programs

If you are willing to compile and execute SQL programs with SQLite DBMS but you do not have a setup for the same, then do not worry. The compileonline.com is available on a high end dedciated server giving you real programming experience with a comfort of single click execution. Yes! it is absolutely free and its online.

SQL - Quick Guide

What is SQL?

SQL is structured Query Language which is a computer language for storing, manipulating and retrieving data stored in relational database.
SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server uses SQL as standard database language.
Also they are using different dialects, Such as:

MS SQL Server using T-SQL,
Oracle using PL/SQL,
MS Access version of SQL is called JET SQL (native format )etc

Why SQL?

Allow users to access data in relational database management systems.
Allow users to describe the data.
Allow users to define the data in database and manipulate that data.
Allow to embed within other languages using SQL modules, libraries & pre-compilers.
Allow users to create and drop databases and tables.
Allow users to create view, stored procedure, functions in a database.
Allow users to set permissions on tables, procedures, and views

What is RDBMS?

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd.

What is table ?

The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows.
Remember, a table is the most common and simplest form of data storage in a relational database.

What is field?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.
A field is a column in a table that is designed to maintain specific information about every record in the table.

What is record, or row?

A record, also called a row of data, is each individual entry that exists in a table. For example there are 7 records in the above CUSTOMERS table.
A record is a horizontal entity in a table.

What is column?

A column is a vertical entity in a table that contains all information associated with a specific field in a table.

What is NULL value?

A NULL value in a table is a value in a field that appears to be blank which means A field with a NULL value is a field with no value.
It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation.

SQL Constraints:

Constraints are the rules enforced on data columns on table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database.
Contraints could be column level or table level. Column level constraints are applied only to one column where as table level constraints are applied to the whole table.

SQL Syntax:

SQL is followed by unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax:
All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;).
Important point to be noted is that SQL is case insensitive which means SELECT and select have same meaning in SQL statements but MySQL make difference in table names. So if you are working with MySQL then you need to give table names as they exist in the database.

SQL SELECT Statement:

SELECT column1, column2....columnN
FROM   table_name;

SQL DISTINCT Clause:

SELECT DISTINCT column1, column2....columnN
FROM   table_name;

SQL WHERE Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION;

SQL AND/OR Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION-1 {AND|OR} CONDITION-2;

SQL IN Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name IN (val-1, val-2,...val-N);

SQL BETWEEN Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name BETWEEN val-1 AND val-2;

SQL Like Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name LIKE { PATTERN };

SQL ORDER BY Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION
ORDER BY column_name {ASC|DESC};

SQL GROUP BY Clause:

SELECT SUM(column_name)
FROM   table_name
WHERE  CONDITION
GROUP BY column_name;

SQL COUNT Clause:

SELECT COUNT(column_name)
FROM   table_name
WHERE  CONDITION;

SQL HAVING Clause:

SELECT SUM(column_name)
FROM   table_name
WHERE  CONDITION
GROUP BY column_name
HAVING (arithematic function condition);

SQL CREATE TABLE Statement:

CREATE TABLE table_name(
column1 datatype,
column2 datatype,
column3 datatype,
.....
columnN datatype,
PRIMARY KEY( one or more columns )
);

SQL DROP TABLE Statement:

DROP TABLE table_name;

SQL CREATE INDEX Statement :

CREATE UNIQUE INDEX index_name
ON table_name ( column1, column2,...columnN);

SQL DROP INDEX Statement :

ALTER TABLE table_name
DROP INDEX index_name;

SQL DESC Statement :

DESC table_name;

SQL TRUNCATE TABLE Statement:

TRUNCATE TABLE table_name;

SQL ALTER TABLE Statement:

ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype};

SQL ALTER TABLE Statement (Rename) :

ALTER TABLE table_name RENAME TO new_table_name;

SQL INSERT INTO Statement:

INSERT INTO table_name( column1, column2....columnN)
VALUES ( value1, value2....valueN);

SQL UPDATE Statement:

UPDATE table_name
SET column1 = value1, column2 = value2....columnN=valueN
[ WHERE  CONDITION ];

SQL DELETE Statement:

DELETE FROM table_name
WHERE  {CONDITION};

SQL CREATE DATABASE Statement:

CREATE DATABASE database_name;

SQL DROP DATABASE Statement:

DROP DATABASE database_name;

SQL USE Statement:

USE DATABASE database_name;

SQL COMMIT Statement:

COMMIT;

SQL ROLLBACK Statement:

ROLLBACK;

SQL - Operators:

SQL Arithmetic Operators:

Assume variable a holds 10 and variable b holds 20 then:
Show Examples

Operator	Description	Example
+	Addition - Adds values on either side of the operator	a + b will give 30
-	Subtraction - Subtracts right hand operand from left hand operand	a - b will give -10
*	Multiplication - Multiplies values on either side of the operator	a * b will give 200
/	Division - Divides left hand operand by right hand operand	b / a will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	b % a will give 0

SQL Comparison Operators:

Assume variable a holds 10 and variable b holds 20 then:
Show Examples

Operator	Description	Example
=	Checks if the value of two operands are equal or not, if yes then condition becomes true.	(a = b) is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(a != b) is true.
<>	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(a <> b) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(a > b) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(a < b) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(a >= b) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(a <= b) is true.
!<	Checks if the value of left operand is not less than the value of right operand, if yes then condition becomes true.	(a !< b) is false.
!>	Checks if the value of left operand is not greater than the value of right operand, if yes then condition becomes true.	(a !> b) is true.

SQL Logical Operators:

Here is a list of all the logical operators available in SQL.
Show Examples

Operator	Description
ALL	The ALL operator is used to compare a value to all values in another value set.
AND	The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause.
ANY	The ANY operator is used to compare a value to any applicable value in the list according to the condition.
BETWEE N	The BETWEEN operator is used to search for values that are within a set of values, given the minimum value and the maximum value.
EXISTS	The EXISTS operator is used to search for the presence of a row in a specified table that meets certain criteria.
IN	The IN operator is used to compare a value to a list of literal values that have been specified.
LIKE	The LIKE operator is used to compare a value to similar values using wildcard operators.
NOT	The NOT operator reverses the meaning of the logical operator with which it is used. Eg. NOT EXISTS, NOT BETWEEN, NOT IN etc. This is negate operator.
OR	The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause.
IS NULL	The NULL operator is used to compare a value with a NULL value.
UNIQUE	The UNIQUE operator searches every row of a specified table for uniqueness (no duplicates).

SQL - Useful Functions:

SQL has many built-in functions for performing processing on string or numeric data. Following is the list of all useful SQL built-in functions:

SQL COUNT Function - The SQL COUNT aggregate function is used to count the number of rows in a database table.
SQL MAX Function - The SQL MAX aggregate function allows us to select the highest (maximum) value for a certain column.
SQL MIN Function - The SQL MIN aggregate function allows us to select the lowest (minimum) value for a certain column.
SQL AVG Function - The SQL AVG aggregate function selects the average value for certain table column.
SQL SUM Function - The SQL SUM aggregate function allows selecting the total for a numeric column.
SQL SQRT Functions - This is used to generate a square root of a given number.
SQL RAND Function - This is used to generate a random number using SQL command.
SQL CONCAT Function - This is used to concatenate any string inside any SQL command.
SQL Numeric Functions - Complete list of SQL functions required to manipulate numbers in SQL.
SQL String Functions - Complete list of SQL functions required to manipulate strings in SQL.

Heavy rains in Rajasthan, Delhi disrupt normal life

noreply@blogger.com (Hamid) — Fri, 24 Aug 2012 22:25:00 +0530

Jaipur/ New Delhi: Heavy rains have thrown normal live out of gear in several parts of the country including Rajasthan and the Delhi-NCR region.

The Rajasthan Meteorological Department has predicted more rains even as 27 have died in two days of torrential rain in the state. According to the Met heavy rainfall is expected in Tonk and Jaipur in the next 24 hours. Of the 27 people who have lost their lives, 10 are from Jaipur.
The worst affected districts in the state are Sikar, Sawai Madhopur, Nagaur and Jhunjhunu. However, there was some respite for Jaipur and nearby areas as there was no rain during the intervening night of Thursday and Friday, making it easier for relief workers to speed up their work.
courtesy: IBN

20 Ideas to make Money Online

noreply@blogger.com (Hamid) — Tue, 5 Apr 2011 12:41:00 +0530

courtesy: business today
A cash cow for the enterprising, the Internet is littered with opportunities to make a fast buck. While it rarely qualifies as a solitary source of income, the Net can easily help you supplement it. However, the amount you earn depends on the time and effort invested. Go through these 20 options and find out which ones work for you.

Blogging
If you're a passionate closet writer who wants to be published but can't find a way to do so, make each keystroke your way to wealth by penning your own blog. Starting a blog doesn't require extensive technical skills but it's important that you have expertise in the field you are writing on. This will attract visitors to your site. Building a large following will enable you to earn profit by luring advertisers, writing paid reviews or getting commissions for promoting other people's products.

Paid Writing
If maintaining a blog is difficult for you but you still want to indulge your passion for writing, you can jot down articles for other blogs or sites such as Weblogs, Helium or PayPerPost. Writing an e-book can also be a good option. E-books are investment free, with no cost for printing and shipping. If you have a strong command over languages, you can become a copy editor, where Webmasters will pay you to read articles and correct grammatical errors, sentence fragments, etc.

e-tuitions/Webinars
The demand for tutors is high and growing. So, if you like helping others learn, e-teaching could be the earning ticket for you. All you need to become an online tutor is expertise in your subject and a few spare hours per week. TutorVista, e-tutor, SmartThinking and Tutor.com are some of the sites you can enroll with. If you gain a good reputation as a coach, you could even conduct Webinars-lectures or seminars transmitted over the Net. College and university students are willing to pay to gain entry to a well-respected Webinar.

Affilliate/Reseller
For those who have the knack of selling, one of the best ways to make money online is to become an affiliate/reseller. An affiliate is a person who gets a commission for selling every product that he promotes, whether on his Website or through any other avenue such as eBay. You don't have to own the product. You only need to sign up for an affiliate program with a company and start selling its products under your referral link. Firms such as Commission Junction or Click Bank have a large pool of products.

Buying/Selling domains
Buying and selling domain names is another way to make money from home and requires very little investment or time. You can buy domains at their registration prices or even cheaper and trade them at a profit. However, always research on sites such as sedo.co.uk, afternic.com, ebay.com or other domain auction sites to get an estimate of the hottest selling names. The best way to find good ones is to use terminated domain lists, which contain several expired names that are back in the pool.

Freelancing for Professionals
Freelancing is a great option for professionals who are experts in their respective trades and know how to ensure customer satisfaction. Various freelancing and project-oriented sites allow companies that need help to describe their projects. Freelancers and small businesses offer bids, ideas or proposals, from which the buyers can choose what they find most suitable. Websites such as Elance cover everything from programming and writing to data entry and design, while RentACoder focuses on software programming.

Advertising
You can sell space on your Website or blog for advertisements and you earn when these ads are clicked by visitors to your site. The sorting and placing of ads is free. The profitability of pay-per-click advertising depends on the traffic level of the Website and, most importantly, on the clickthrough rate and cost per click. Google AdSense is the most popular option, while others are BidVertiser, Text Link Ads and Blogads. Direct banner and RSS feed are some other forms of online advertising.

GPT Programme
GPT or Get-paid-to sites are becoming increasingly popular among teens. You get paid for signing up for free Websites, newsletters, playing games and filling out online surveys. These are suitable for people who don't have a skill set but want to earn extra money. Taking online surveys is simple- register with a few legitimate, paid survey sites and answer questions. The topics range from shopping to politics. This might not help you make a living, but you can earn good pocket money. Contests2win is one of the trusted GPT Websites.

Online Marketing
Once a Website is created and optimised for search engine (SEO), the SEM or Search Engine Marketing begins. A treasure trove lies hidden here. An SEO/SEM expert, who is responsible for marketing a Website, can promote it in various ways. These include article marketing, writing press releases, forum posting, blog posting, submitting your site to directories and search engines, social bookmarking, etc. Most companies don't do this in-house and pay you to conduct the SEM for them.

Making themes
As more and more people seek an online presence, the demand for Website templates and WordPress (Blog) themes will keep increasing. If you are good at Web designing and coding, you can earn a lot from designing Web themes. In this segment, there are mainstream Websites, such as TemplateMonster and ThemeForest, which act as a marketplace where you can sell your themes. Templates are sold and priced depending on the rights and features that are bundled with them.

Selling photos
If you enjoy photography and are good with a camera, you could be sitting on a huge reserve of revenue. There are people who will be interested in your collection of images. Nowadays, it's easy to take your photos to the public, providing a convenient way to build a secondary income stream. Many stock photo agencies, such as Fotolia, Dreamstime and Shutterstock, offer incentives for people to earn from their photos.

Support & service
Providing coding or fixing other Webmasters' issues is another great way to earn extra bucks. There are simple jobs ranging from adding a script to setting up sites, but knowledge of Web coding is essential. One can offer support for Web CMS (content management systems) like Drupal or Joomla. After you are comfortable with your own installation, you can help other people to set these up and configure them.

Stock/forex trading
Joining the stock/forex market may seem a bit risky. However, you can start small and continue researching till you gain experience in this area. Once you do, it will be easy to earn from exchanging foreign currencies and/or stocks. Their rates fluctuate depending on supply and demand, and economic and political influences in the world. The aim of any trader is to spot which currency/stock is likely to rise or fall in value against another. The more time you put in, the more you will earn.

Selling your own brand
If you have a flair for designing cool images, don't bother about creating your own inventory. As long as your design can be printed on a product, you can pocket some money. You can upload designs on various Websites such as CafePress, and if somebody orders these designs, the company will print them and distribute the products. It could be designs for T-shirts, hats, bags, books, posters, calendars, greeting cards, etc. You will receive a commission for each sale. Other such sites include Lulu and Zazzle.

Virtual Assistant
Small businesses always need help in running their processes, but may not be willing to hire a full-time employee. As a virtual assistant, you are expected to perform practically any administrative task that a traditional secretary or assistant would, such as make travel reservations, handle expense reimbursements or pay bills. You can do it from the comfort of your home, interacting with clients either online or by phone. Your expertise will decide how much moolah you rake in.

Inbound call centre
Many companies, who are facing space constraints, especially those in metro cities, prefer to hire workers outside their offices or outsource certain processes. You can set up an inbound call centre at home to handle such jobs. Research different companies that are outsourcing their work as they may have opportunities for inbound call centre agents. You can work for more than one company. This can be either a part-time or fulltime engagement, depending on your need.

You Tube
If there's a dramatic performer hidden inside you who craves applause and adulation, upload yourself on YouTube. You can be a filmmaker, musician or comedian who wants a wider audience. Your earnings will come from ads displayed on your video page. This process is similar to the pay-per-click advertising program common to other Websites and blogs. Sites such as Flixya and Mediaflix can be helpful in this regard.

Researching for others
Don't be morose if you can't write, design or code. Lack of talent cannot stop you from making money online. If you're willing to work hard for a few hours a week, you can take up simple research jobs for other people who don't have the time to do it themselves. You could search for opportunities in organisations that provide funding for research and offer to assist them through online investigation.

Building Applications
With smartphones gaining popularity, the demand for their applications, or apps as they are popularly known, has also shot up. There are over 3 million apps for the iPhone and over a million apps in Google's Android market. Most of these are selling like hot cakes. Developing and selling your own smartphone app is becoming a lucrative way to make money on the Internet. Apps cost virtually nothing to develop and entail no storage or shipping costs. So they enjoy the best profit margins.

Transcription
Medical transcription involves making written copies of oral material dictated by doctors or other medical experts. These may include history and physical reports, clinical notes, consultation notes, reports, letters, psychiatric evaluation and so on. The dictated material needs to be transcribed swiftly and accurately, which is the most challenging aspect of the job. To become a medical transcriptionist, you need to have a good knowledge of medical terminology and a high typing speed along with accuracy.