To calculate a MD5 checksum of any file, enter the following command at the Windows command prompt:
certUtil -hashfile <file_to_check> MD5

To calculate a SHA-1 checksum of any file, enter the following command at the Windows command prompt:
certUtil -hashfile <file_to_check> SHA1

To calculate a MD5 checksum of any file, enter the following command at the Linux prompt:
md5sum <file_to_check>

To calculate a SHA-1 checksum of any file, enter the following command at the Linux prompt:
sha1sum <file_to_check>

You are probably doing nothing wrong but hit an arbitrary restriction imposed by JDK with default settings. The restriction turns out that the cryptography classes in Java will not allow encryption with a key size of more than 128 bits. The main reason for the restriction is that some countries have restrictions on the permitted key strength of imported encryption software. So, it is the user’s responsibility to verify that this action is permissible under local regulations.

Download JCE Unlimited Strength Jurisdiction Policy Files

If you really need to override the restriction (for example you need to use AES with 256-bit keys), you need download the JCE Unlimited Strength Jurisdiction Policy Files from Java and install the files into your JDK/JRE folder.

• JCE Unlimited Strength Jurisdiction Policy Files for Java 6
• JCE Unlimited Strength Jurisdiction Policy Files for Java 7
• JCE Unlimited Strength Jurisdiction Policy Files for Java 8

Steps to install the JCE Unlimited Strength Jurisdiction Policy Files

1. Backup the files in ${java.home}/jre/lib/security/ in case the downloaded file does not work.
2. Download the JCE Unlimited Strength Jurisdiction Policy according to you Java version.
3. Decompress the zip file.
4. Replace all the files in ${java.home}/jre/lib/security/ with the new decompressed files.

By changing the default administrator username of your WordPress login can be a great security measure to help prevent unauthorized access to your WordPress admin dashboard. Your WordPress site is at risk if you are still using the default username admin. Attackers, either a human being or a robot can use the username to attempt log into your WordPress dashboard.

It is always good practice to use an username that is meaningful but difficult to be guessed by the other. You should always avoid using usernames like admin, administrator or using username from your domain name directly.

The old WordPress installation used the username admin by default. WordPress sites upgraded from older version should change the default administrator username. While the new WordPress installation will prompt user to enter a new username for the administrator. So be wise to choose a good username.

The following steps show how to change your username without installing any plugin or needing of access to the database:

1. Login to your WordPress site using your current administrator account.
2. Hover over the “Users” link on the menu on the left, then click “Your Profile”.
3. Change your email address to other email address (any will do). Save changes by clicking the “Update Profile” button. This step is important if you want to reuse your email address for your new administrator account.
4. Hover over the “Users” link on the menu on the left, then click “Add New”.
5. Key in all the required field. You can use the email previously set for the current Administrator.
6. Be sure to choose “Administrator” for the role.
7. Click “Add New User” to save the changes.
8. Logout current user and login into the new user you have created just now.
9. Hover over the “Users” link on the menu on the left, then click “All Users”.
10. Hover over the old admin user, then click “Delete”. Make sure you select your new admin user from the “Attribute all posts” drop-down, and click on “Confirm Deletion” (Important!).
11. Done.

Your WordPress site is now better protected against common brute force attempts.

Sometime, you may want to compress all files in a folder (or folders) in Linux into a single file to save space and so that you can back up the file to other media. In Linux, you can use the tar utilities which is installed in most Linux distribution by default.

GNU ‘tar’ saves many files together into a single tape or disk archive, and can restore individual files from the archive.

What the utility does is actually it creates an archive of the specified files and then compress the archive. Creating an archive of files is like dumping all the files content into a single file and some dictionary data (name and size of each file) so that you can extract files from the archive later on.

How to compress files and folders

To compress files and folders into a single file:

[bash title=”Syntax:”]tar -czvf output-file input-folders-or-files[/bash]

where

• c – create a new archive
• z – filter the archive through gzip
• v – verbosely list files processed
• f – use archive file
• output-file – the output file
• input-folders-or-file – multiple input folders or files

For example, to create a compressed archive file from the /home/user1 and /home/user2 folder:

[bash title=”Example:”]tar -czvf backup.tar.gz /home/user1 /home/user2[/bash]

It is a good practice to put the output file name with tar.gz extension so that we know that the file is created from the tar utility and it is compressed.

How to decompress and extract files and folders from a compressed tar archive

To decompress files and folders from a compressed tar archive:

[bash title=”Syntax:”]tar -xzvf input-file[/bash]

where

• x – extract files from an archive
• z – filter the archive through gzip
• v – verbosely list files processed
• f – use archive file
• input-file – the compressed archive file

For example, to decompress and extract files from an compressed archive file:

[bash title=”Example:”]tar -xzvf backup.tar.gz /home/user1 /home/user2[/bash]

tar has many other options and uses as well. Do reading through its man page for more options.

eGenting Programming Competition 2015 is coming this November and it is now open for registration. The layout or the format of the competition is remain unchanged except that eGenting Sdn Bhd is also having another competition – eGenting Bug Hunt – on next day of the eGenting Programming Competition.

What is eGenting Programming Competition

The E-Genting Programming Competition is an annual programming competition organised by E-Genting to hire programming talent for its Systems Research & Development department, which maintains the backbone system used by Genting casinos all over the world.

Tips for eGenting Programming Competition 2015

No tips on the questions but these are the basic things you should know:

• Get familiar with at least two programming languages.
• Get familiar with SQL and DBMS, be it embedded or not.
• Get a deep understanding in data structure and algorithms like array, queue, set, stack, map, trees, object, sorting, searching and data parsing.
• Only bring the book you really need and you may consider to share books with your friends.
• Plan your time and code. Try modularize your code, it may help you save time on rewriting same portion of code at different places.
• Bring your jacket. The competition hall is cold.
• Do check back and try out past year questions.

Details of eGenting Programming Competition 2015

Date And Time Of The Competition

• Date: 14 November 2015 (Saturday)
• Time: 10:00 AM to 6:00 PM

Contact

• Tel: +603 2333 3276
• Email: cheeleng.tan@rwgenting.com

Address

Auditorium, 25th Floor Wisma Genting, Jalan Sultan Ismail, 50250 Kuala Lumpur, Malaysia.

Map Location

Competition Style

The competition is an open-book hand-written programming competition. You will be given a question paper with four different specifications. You are required to design and write a program to ensure that it satisfies the requirements or to solve the problems described in the specification. You are not required to answer all the questions.

Meals

Breakfast, lunch and tea break will be provided during the competition.

Prizes

• First prize – RM6,000 + *Job Offer
• Second prize – RM3,000 + *Job Offer
• Third prize – RM2,000 + *Job Offer
• Distinction – RM500 + *Job Offer (Multiple prizes)
• Merit – RM200 + *Job Offer (Multiple prizes)

* Subject to terms and conditions

Registration

http://egpc.genting.com.my/Registration.aspx

Terms and Conditions

http://egpc.genting.com.my/Terms.aspx

eGenting Bug Hunt Facebook Page

https://www.facebook.com/egentingpc

eGenting Bug Hunt 2015 is coming this November and the registration is now open.  This will be the third year the company organizing the annual event and it will be different from the past few years.

What is eGenting Bug Hunt?

The eGENTING Bug Hunt is an annual software testing competition organized by eGenting Sdn Bhd to hire the best software quality assurance engineers. Contestants will be given a software specification and a software source code that theoretically confirms to the specification. Contestants are required to return a test procedures that can be used to test the software given and to detect potential bugs at the end of the competition.

How this year’s competition different from the past?

In the past competitions, there were two round of tests. In the first round, contestants are given a specification and a software program source code that theoretically conforms to the specification. Contestants are required to return a test procedures, a test results and optionally the corrected source code within 3 days via email. Contestants that return credible answer will be selected into second round. In the second round, contestants are invited to run the similar test at Wisma Genting with a computer provided.

eGenting Bug Hunt 2015 will be different. It is a full day, single round single shot competition. The competition will start at 10am in the morning and end 6pm in the evening. In line with the eGenting Programming Competition, it is a hand-writing and open books competition, therefore no computer will be provided. No electronic device is allowed during the competition. The competition will be held at the Wisma Genting’s auditorium.

Tips for eGenting Bug Hunt 2015?

Ok, you want some tips. These are some that I could think of:

1. Read the specification a few time. Just ask if you have any doubt.
2. Plan your time. Do not spend too much time on fixing the bug. Focus on preparing a quality test plans.
3. Get yourself familiar with the following programming languages:
   • SQL
   • C/C++
   • Java
4. Your test procedures should contain test cases that cover the given specification as much as possible.
5. Testing methods that are important:
   • White box
   • Black box
6. Don’t bring a trolley to carry your books. Believe me, you may not have much time to study in the hall. Two to three of reference books should be more than enough. You can consider to share books with your friends too.
7. Bring your jacket. Your brain may not function optimally if it is too cold in the hall.
8. Read more tips from the eGenting Bug Hunt Workshoup held in Wisma Genting on 19th August 2015.

Details of eGenting Bug Hunt 2015

Date And Time Of The Competition

• Date: 15 November 2015 (Sunday)
• Time: 10:00 AM to 6:00 PM

Contact

• Tel: +603 2333 3276
• Email: cheeleng.tan@rwgenting.com

Address

Auditorium, 25th Floor Wisma Genting, Jalan Sultan Ismail, 50250 Kuala Lumpur, Malaysia.

Map Location

Competition Style

The competition is an open-book hand-written testing procedure design competition. You will be given a specification and C++/Java source code for a program that theoretically conforms to the specification. You are required to design and document testing procedures that verify the program to ensure that it satisfies the requirements described in the specification.

Meals

Breakfast, lunch and tea break will be provided during the competition.

Prizes

• First prize – RM6,000 + *Job Offer
• Second prize – RM3,000 + *Job Offer
• Third prize – RM2,000 + *Job Offer
• Distinction – RM500 (Multiple prizes)
• Merit – RM200 (Multiple prizes)

* Subject to terms and conditions

Registration

http://egbh.rwgenting.com/Registration.aspx

Terms and Conditions

http://egbh.rwgenting.com/Terms.aspx

eGenting Bug Hunt Facebook Page

https://www.facebook.com/egentingbh

All contestants are cordially invited to EGPC and EGBH Prize Presentation

Date: Saturday, 31 January 2015
Venue: Hard Rock Café, Ground Floor, Wisma Concorde, No 2 Jalan Sultan Ismail, 50250 Kuala Lumpur
Time: 11.15am – 3.00pm

• 11.15am Arrival of guests
• 12.00noon Welcome Speech & Competition Debriefing
• 12.30pm Lunch
• 1.30pm Presentation of Prizes and Awards
• 3.00pm End

Why Not A Java Static Constructor?

It is actually not a constructor that initializes the static variables’ value. This is because static variables do not need to and can not be constructed as they are being shared among the instances (object) of the class. The static variables just need to be initialized when the class is first accessed by any code by the Java runtime.

What Is Static Initialization Block?

In Java, it is called “static initialization block”:

A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

Alternatively, you can write a private static method that return values to the static variables. The advantage of private static methods is that they can be reused later if you need to reinitialize the class variable.

Things To Take Note

Static initialization blocks are called in the order that they appear in the source code. You must be careful not to access to the variables that have not been initialized in the static initialization blocks. If you do so, you may encounter a NullPointerException during runtime. It is always painful and time wasting to trace this kind of exception.

[java]public class Example1 {
static Obj obj1;
static Obj obj2;
static Obj obj3;
static {
// First call
obj1 = new Obj();

obj2.something() // This will throw NullPointerException
}
static {
// Second call
obj2 = new Obj();
}
static {
// Third call
obj3 = new Obj();
}
}[/java]

Secondly, the alternative to static blocks, the private static method, are called in the sequence of the static variables being written in the source code.

[java]public class Example2 {
static Obj obj1 = initObj1();
static Obj obj2 = initObj2();
static Obj obj3 = initObj3();;
private static Obj initObj3() {
// Third call
}
private static Obj initObj2() {
// Second call
}
private static Obj initObj1() {
// First call
}
}[/java]

The Simplest Way But Ineffective

The simplest way to pick the top N elements is to sort the whole list and get the top N elements. This method is easy to understand and implement but the overhead is too high. It might take a lot of memory or temporary disk resource if the list is big (especially if you need to load all the data from a file or you simple cannot use the normal SQL sorting method to sort the data) and it will takes lot of comparison during sorting. When the list size goes big, the side effect on performance becomes greater too.

The More Effective Way

The more effective way does not necessary always complicated. You can simply use the fixed-size PriorityQueue in java.util package to achieve the same result but with much better performance. PriorityQueue is based on priority heap and the elements in PriorityQueue are ordered according to their natural ordering.

PriorityQueue provides O(log(n)) time for the enqueing and dequeing methods. To make the elements ordered in natural ordering, you need to make sure the element’s class implements the Comparable interface or provide a appropriate  Comparator instance for the elements.

Below is an example on how to use PriorityQueue to get Top N objects from a list (either loaded from file or database):

public class TopList {
  private T[] tlArray;
  private Comparator tlComparator;
  private PriorityQueue tlHeapSort;

  public TopList(T[] array, Comparator comparator) {
    tlArray = array;
    tlComparator = comparator;
    tlHeapSort = new PriorityQueue(array.length, comparator);
  }

  public void put(T item) {
    if (tlHeapSort.size() < tlArray.length) {
      tlHeapSort.add(item);
    }
    else if (tlComparator.compare(tlHeapSort.peek(), item) < 0) {
      tlHeapSort.poll();
      tlHeapSort.add(item);
    }
  }

  public void finish() {
    int                 i;              // Index

    for (i = tlHeapSort.size() - 1; i >=0 ; i--) {
      tlArray[i] = tlHeapSort.poll();
    }
  }
}

public class Player {
  int score_1;
  int score_2;
  int score_3;
  String name;
}

public static void main (String args[]) {
  Comparator comparator;
  Player[] topPlayers;
  TopList topList;
  Player p;

  topPlayers = new Player[10];
  comparator = new Comparator() {
    @Override
    public int compare(Player o1, Player o2) {
      int diff1, diff2, diff3;

      diff1 = o1.score_1 - o2.score_1;
      if (diff1 != 0) return diff1;
      diff2 = o1.score_2 - o2.score_2;
      if (diff2 != 0) return diff2;
      diff3 = o1.score_3 - o2.score_3;
      if (diff3 != 0) return diff3;
      return 0;
    }
  }
  topList = new TopList(topPlayers, comparator);

  // Load from files or database
  while (/* has records */) {
    p = /* Load a player instance */;
    topList.put(p);
  }
  topList.finish();

  // Print the top winners
  System.out.printf ("TOP PLAYERS\n");
  for (int i = 0; i < topPlayers.length; i++) {
    p = topPlayers[i];
    if (p == null) break;
    System.out.printf ("%d %s (%d, %d, %d)\n", 
      i + 1, p.name, p.score_1, p.score_2, p.score_3);
  }
}

With this implementation, it will not burden your memory and CPU usage, even you have to select only 10 elements out of millions data.

To prevent that from happen, I have made up a plan before I transfer all my websites from my previous hosting to DigitalOcean.

Get New Hosting Account Ready

Before moving your websites to another web hosting, register and get the new hosting account ready. The new account need to be ready a few weeks before your previous web hosting’s contract end. Login in to your new hosting account and try to setup a new website and check the accessibility.

Make sure the new hosting computer has all the software you need to run your websites. If you are using a VPS or dedicated hosting, make sure you have install the latest software supported by the WordPress (if you are running WordPress blogs).

Setup all the user accounts, emails, and database as they were in the old hosting computer.

Transfer Your Websites Files

Backup your websites, including the database backup. Restore websites and database backup at new hosting. You need to do this before changing the name server of your domain name. Test your websites using IP address at your new hosting computer. Make sure they are working properly. Click on links on your page to make sure your websites load correctly.

Install Web Analytics

Install a web analytics on your websites at both old and new hosting, Google Analytics or Statcounter are pretty good. Optionally you can use the web analytics that comes with your hosting package. This is to track whether your visitors are visiting your old or new websites.

Change Name Server

Change the name server of your domain name at your domain name registrar. Changing a name server  can typically take 0 to 24 hours to take effect but it may take days to go into full effect.

Monitor

Try access to your websites using domain name after the name server has been resolved. Use the “ping” utility on your computer to ping to the domain name to check that you are on the right server.

Monitor the web analytic. Since you are now having websites running at both old and new hosting computer, your visitors will slowly moving from your old hosting to the new hosting. The transition might take days or weeks. Until you don’t receive any traffic from your old hosting company, that means your name server is fully resolved. And now you can terminate your old hosting service.

Now you will have minimum down time as the old hosting and new hosting are serving your visitors during this transition period.

From C manual for ungetc:

A character is virtually put back into an input stream, decreasing its internal file position as if a previous getc operation was undone.

This character may or may not be the one read from the stream in the preceding input operation. In any case, the next character retrieved from stream is the character passed to this function, independently of the original one.

Notice though, that this only affects further input operations on that stream, and not the content of the physical file associated with it, which is not modified by any calls to this function.

This is my simple version of ungetc in Java, UInputStream. I use an InputStream as the base class so that you can work with other input stream object like FileInputStream. UInputStream will override the read() function from InputStream and an additional function to undone the read.

import java.io.IOException;
import java.io.InputStream;

public class UInputStream extends InputStream {
    private InputStream uIn;
    private boolean uPushedBack;
    private int uPushedBackVal;

    public UInputStream(InputStream in) {
        uIn = in;
        uPushedBack = false;
        uPushedBackVal = -1;
    }

    @Override
    public int read() throws IOException {
        if (uPushedBack) {
            uPushedBack = false;
            return uPushedBackVal;
        }
        return uPushedBackVal = uIn.read();
    }

    public void unread() {
        if (uPushedBack)
            throw new IllegalStateException("Already pushed back a byte");
        uPushedBack = true;
    }
}

Here is how you use the UInputStream

InputStream in = new UInputStream(/*other stream object*/);
int c;
while ((c = in.read()) != -1) {
    if (c == 'A') {
        in.unread()
        doSomethingStartsWithA(in);
    }
}

Below are the details of the event:

• Competition date: 9 November 2013 (Saturday)
• Time: 10.00 am to 6.00 pm
• Venue: Auditorium, 25th Floor Wisma Genting, Jalan Sultan Ismail, 50250 Kuala Lumpur
• Nature: Open-book handwritten programming task

The prizes:

• 1st Prize – RM6,000
• 2nd Prize – RM3,000
• 3rd Prize – RM2,000

For registration and question, please email cheeleng.tan@rwgenting.com for more information.

EGPC Website: http://egpc.genting.com.my

ID   COL1   COL2   COL3
======================
1    100    200    300
2    200    300    400
3    100    200    500
4    300    300    300
5    200    300    400

And the expected result is ID = 1,2,3,5. The SQL to achive the result is:

select 
    left.ID
from
    t1 left inner join t1 right
on
    left.COL1 = right.COL1 and
    left.COL2 = right.COL2 and
    left.ID <> right.ID

You can also use “group by” then “count(*)” method but it is a bit more complicated and slow.

The process of moving out the pages for physical memory to disk is called swapping. The size of “memory on disk” is depending on the swap file size. The combination of physical memory and the “memory on disk” is called virtual memory. Therefore, you can have virtually unlimited memory.

Swapping has it disadvantage – it is slow when Linux need to keep swapping in and out of memory pages. It is slow because of the disk speed limitation. But if you have a server running with SSD disk (solid-state disk), you may not feel the pain. However, the process is required to make sure the operating system can works under memory pressure.

Check for Existing Swap File
Execute the following command to check for the existing swap space:
swapon -s

Check for Available Disk Space
Execute the following command to check for disk space availability.
df -h

Create Swap File
Execute the following command to create a swap file of size 1Gb. The following command will write zero values with block size 1024 bytes 1024k times to file “swapfile”.
sudo dd if=/dev/zero of=/swapfile bs=1024 count=1024k

Enable Swap File
Execute the following command to make the file a swap space.
sudo mkswap /swapfile

Start Using Swap File
Execute the following command to let the operating system know the swap file is now ready to use.
sudo swapon /swapfile

Set Swap File Permission
Execute the following commands to ensure the swap file has the correct file permission:
chown root:root /swapfile
chmod 0600 /swapfile

Done
Execute swapon -s to ensure the swap file is being used.

Enable Swap File Durinn Boot Up
When the machine reboot, operating system will not use the swap file again. You can ensure that the swap is permanently loaded by adding it to the fstab file. Edit the file “/etc/ftab” and add the following line:
/swapfile swap swap defaults 0 0