Anuj's Share IT

Java 8 JMX Default Metrics

2016-04-07T21:31:00.001-07:00

This is more of a note. Here you can find default types and attributes for JMX on top of Java 8.

Code: I will clean and explain it later :(


private static void WriteAttributes(final MBeanServer mBeanServer, final ObjectName http)
            throws InstanceNotFoundException, IntrospectionException, ReflectionException
    {
        MBeanInfo info = mBeanServer.getMBeanInfo(http);
        MBeanAttributeInfo[] attrInfo = info.getAttributes();

        System.out.println("Attributes for object: " + http +":\n");
        for (MBeanAttributeInfo attr : attrInfo)
        {
            System.out.println("  " + attr.getName() + "\n");
        }
    }

Attributes for object: java.lang:type=MemoryPool,name=Metaspace:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: java.lang:type=MemoryPool,name=PS Old Gen:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: java.lang:type=GarbageCollector,name=PS Scavenge:

LastGcInfo

CollectionCount

CollectionTime

Name

MemoryPoolNames

Valid

ObjectName

Attributes for object: java.lang:type=MemoryPool,name=PS Eden Space:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: JMImplementation:type=MBeanServerDelegate:

MBeanServerId

SpecificationName

SpecificationVersion

SpecificationVendor

ImplementationName

ImplementationVersion

ImplementationVendor

Attributes for object: java.lang:type=Runtime:

Name

ClassPath

BootClassPathSupported

VmName

VmVendor

VmVersion

LibraryPath

BootClassPath

Uptime

StartTime

SpecName

SpecVendor

SpecVersion

ManagementSpecVersion

InputArguments

SystemProperties

ObjectName

Attributes for object: java.lang:type=Threading:

ThreadAllocatedMemorySupported

ThreadAllocatedMemoryEnabled

ThreadContentionMonitoringSupported

CurrentThreadCpuTimeSupported

ObjectMonitorUsageSupported

SynchronizerUsageSupported

ThreadContentionMonitoringEnabled

ThreadCpuTimeEnabled

PeakThreadCount

DaemonThreadCount

ThreadCount

TotalStartedThreadCount

AllThreadIds

CurrentThreadCpuTime

CurrentThreadUserTime

ThreadCpuTimeSupported

ObjectName

Attributes for object: java.lang:type=OperatingSystem:

OpenFileDescriptorCount

MaxFileDescriptorCount

CommittedVirtualMemorySize

TotalSwapSpaceSize

FreeSwapSpaceSize

ProcessCpuTime

FreePhysicalMemorySize

TotalPhysicalMemorySize

SystemCpuLoad

ProcessCpuLoad

Name

AvailableProcessors

Arch

Version

SystemLoadAverage

ObjectName

Attributes for object: java.lang:type=MemoryPool,name=Code Cache:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: java.nio:type=BufferPool,name=direct:

Name

Count

TotalCapacity

MemoryUsed

ObjectName

Attributes for object: java.lang:type=Compilation:

Name

CompilationTimeMonitoringSupported

TotalCompilationTime

ObjectName

Attributes for object: java.lang:type=MemoryManager,name=CodeCacheManager:

Name

MemoryPoolNames

Valid

ObjectName

Attributes for object: java.lang:type=MemoryPool,name=Compressed Class Space:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: java.lang:type=Memory:

Verbose

ObjectPendingFinalizationCount

HeapMemoryUsage

NonHeapMemoryUsage

ObjectName

Attributes for object: java.nio:type=BufferPool,name=mapped:

Name

Count

TotalCapacity

MemoryUsed

ObjectName

Attributes for object: java.util.logging:type=Logging:

ObjectName

LoggerNames

Attributes for object: java.lang:type=MemoryPool,name=PS Survivor Space:

Name

Type

Valid

Usage

PeakUsage

MemoryManagerNames

UsageThreshold

UsageThresholdExceeded

UsageThresholdCount

UsageThresholdSupported

CollectionUsageThreshold

CollectionUsageThresholdExceeded

CollectionUsageThresholdCount

CollectionUsage

CollectionUsageThresholdSupported

ObjectName

Attributes for object: java.lang:type=ClassLoading:

TotalLoadedClassCount

LoadedClassCount

UnloadedClassCount

Verbose

ObjectName

Attributes for object: java.lang:type=MemoryManager,name=Metaspace Manager:

Name

MemoryPoolNames

Valid

ObjectName

Attributes for object: com.sun.management:type=DiagnosticCommand:

Attributes for object: java.lang:type=GarbageCollector,name=PS MarkSweep:

LastGcInfo

CollectionCount

CollectionTime

Name

MemoryPoolNames

Valid

ObjectName

Attributes for object: com.journaldev.jmx:type=SystemConfig:

ThreadCount

SchemaName

Attributes for object: com.sun.management:type=HotSpotDiagnostic:

DiagnosticOptions

ObjectName

How to set JAVA_HOME environment variable on Mac

2014-08-08T04:39:00.002-07:00

Note: This tip is for Mac OSX 10.5 or later

Apple recommends to set the $JAVA_HOME variable to /usr/libexec/java_home, just export $JAVA_HOME in file ~/. bash_profile

You might not have .bash_profile present on your system already. No worries we will create/update the profile in next step.

Open Terminal:

$ vi ~/.bash_profile

Initially the vi editor will not be in edit mode, press 'i'.

Update file by exporting variable:

export JAVA_HOME=$(/usr/libexec/java_home)

to the file (in the vi editor which we opened using the previous command)

Saving and Closing the .bash_profile file opened inside vim editor:

Press escape (while still inside the vi editor)

type ":wq!" or press "Shift + zz" to save and exit the file.

Laravel XAMPP MySQL artisan migrate install error mysql.sock

2014-01-20T23:49:00.003-08:00

In my previous post I wrote about setting up Laravel 4 on Mac with XAMPP. When I tried to use migrations (using artisan) I faced some issue. I will also post about Laravel migrations soon.

 php artisan migrate:install

Error:

  [PDOException]                                    

  SQLSTATE[HY000] [2002] No such file or directory

Solution:
We need to tell artisan which mysql we want it to use. For this to work we need to porivde it with mysql.sock which we want it to use.

So change your database settings like this:

'mysql' => array(
   'driver'    => 'mysql',
   'host'      => 'localhost',
   'unix_socket' => '/Applications/xampp/xamppfiles/var/mysql/mysql.sock',
   'database'  => 'wedding',
   'username'  => 'root',
   'password'  => '',
   'charset'   => 'utf8',
   'collation' => 'utf8_unicode_ci',
   'prefix'    => '',
  ),

We need to provide "unix_socket".

On mac it will be find at "/Applications/xampp/xamppfiles/var/mysql/mysql.sock" assuming that you have your XAMPP installed correctly in Applications folder.

References:
http://stackoverflow.com/questions/14219692/laravel-setup-of-migrations-using-artisan-is-failing
http://www.jroller.com/jnicho02/entry/setting_up_xampp_on_the

Working with MySQL on MAC. GUI Client, Web Based and Terminal

2014-01-18T10:46:00.003-08:00

MySQL is most popular open source relational database. I have been using it myself for my PHP, Python and Ruby projects. Obviously, we need some client(s) to access MySQL database. In this post I am going to list down few clients.

Environment:

I am using XAMPP on Mac. You can install MySQL separately if you want to.

1. Desktop GUI client

Use SequelPro it is a nice tool and free.

Set it up and you are ready to go.

2. PHPMyAdmin

phpMyAdmin is a free software tool written in PHP, intended to handle the administration of MySQL over the Web. It gets setup with XAMPP.

3. Terminal

Open up terminal and execute following commands -

Go to the directory with mysql binaries

cd /Applications/XAMPP/xamppfiles/bin;

Access mysql command line tool using

./mysql --user=root --password=

Setting Up Laravel 4.x on Mac OSX 10.8+ with XAMPP installed

2014-01-16T13:06:00.000-08:00

I am new to PHP and have coded earlier with CodeIgniter. It is really easy to get started with CodeIgniter as it is light but powerful and has less features. As CodeIgniter is slowly phasing out I thought of moving to Laravel. Yes, it is powerful and AWESOME!!!

Lets get down to business.

1. Install composer

I was doing it for the first time and faced issues:

Some settings on your machine make Composer unable to work properly.
Make sure that you fix the issues listed below and run this script again:

The detect_unicode setting must be disabled.
Add the following to the end of your `php.ini`:
detect_unicode = Off
A php.ini file does not exist. You will have to create one.

I was clueless at this moment and started to search. After some search I found an article which tells about setting up AMP (Apache, My SQL and PHP) environment.

While going through it I realized that I have Apache already installed on my system (I am new to Mac too). I followed the steps to configure it (took related path accidentally :D).

While doing this I found out that I am working in a system folder /etc. To check it out I jumped into it and to my surprise I found my missing php.ini.default.I created a copy of it, renamed it and opened it up in vim editor.

sudo vi php.ini

I added the line

detect_unicode = Off

at the end.

I tried to setup composer again and it worked.

2. Install Laravel

composer create-project laravel/laravel --prefer-dist

No surprises, I got another issue :D

Script php artisan optimize handling the post-update-cmd event returned with an error:


  [InvalidArgumentException]
  Command "optimize" is not defined.

I found out that mcrypt is not available. I searched again and realized that PHP version which I am using is old. I check it using "php -v" and checked the path of PHP which is being used using "which php". PHP version was 5.3.x.

3. Update PHP (Laravel needs a recent version)

I used this link (It is awesome, thanks to author).

#2. Go back to step 2.

Try again. I thought of using my XAMPP's Apache and tried creating project there. I faced the same issue. Why now :(. I thought it is something to do with PHP version that I am using. I checked the version again and found out that I am still using wrong version and php binaries from wrong path were being used.

I searched to find out how to use the right PHP version and found this Laravel forum link.

I am pasting the suggestion here for ready reference but all the credit goes to the contributor in forum.

You are using the built in version of PHP, did you install PHP-OSX for 5.4 installation? If so you need to overwrite it's path
from terminal:

sudo vi ~/.bash_profile
enter password
when file loads press A to access writing

paste this line:

export PATH=/usr/local/php5/bin:${PATH}

press ESC key

hold SHIFT and Press ZZ (z twice)

now do which php again it should say:

/usr/local/php5/bin/php

now install home brew and you can do stuff like like 
brew install php54-mcrypt

restart apache in between steps

you may also be able to do other stuff like "brew search php54-module" or php54-* to see whats available.. always install with php54 to avoid conflicts.

My setup just worked. I did not need to install homebrew and perform rest of the steps.

For setting up mcrypt you can also refer this link I did not tried it though.

4. Tried http://localhost/laravel/public/ - did not work.

I got Laravel 4 blank screen issue (as people call it famously). I recalled that I need to set storage directory present in app directory of laravel setup as writable.

$ sudo chmod -R 7777 app/storage

As, I am the only user of my machine and this is my home machine I gave all permissions. Please provide appropriate permissions in your case.

5. Happy Ending!!! It worked. :D

Create custom UITextFields and UITextViews with underline

2013-07-07T21:48:00.003-07:00

Download

In a recent iOS project I needed to create custom UITextView and UITextField. The look and feel had to be same as the Notes app, i.e. the text view and text field both should have horizontal lines as are present in a note.

How to create a custom UIView
To create a custom UIView we need to inherit from UIView class. We then need to override drawRect method. Override only if you need to change the way view is drawn as this is a performance intensive operation.

Custom UITextField
In order to create custom UITextField I inherited my class from UITextField. I need to draw a bottom border for this I need override drawRect method.


    //Get the current drawing context
    CGContextRef context = UIGraphicsGetCurrentContext();
    //Set the line color and width
    CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);
    CGContextSetLineWidth(context, 0.5f);
    //Start a new Path
    CGContextBeginPath(context);
    
    // offset lines up - we are adding offset to font.leading so that line is drawn right below the characters and still characters are visible.
    CGContextMoveToPoint(context, self.bounds.origin.x, self.font.lineHeight + 6.0f);
    CGContextAddLineToPoint(context, self.bounds.size.width, self.font.lineHeight + 6.0f);
    
    //Close our Path and Stroke (draw) it
    CGContextClosePath(context);
    CGContextStrokePath(context);

We need to grab a graphic context us we are going to draw a custom UI. Then we need to set color to the context and the line width. Line width, because we need a line under our control. Now, the tricky part:

We need to set the start and end coordinates for line. For this we need the line height so that we can set the Y coordinate correctly. Fortunately iOS provides a simple to get this. self.font.lineHeight. Using this we are asking the view to tell us about the lineHeight based on the font.

Thats it.

Custom UITextView
Approach remains same here. But, we need multiple lines and we need lines to appear even if we scroll.


- (void)drawRect:(CGRect)rect {
    
    //Get the current drawing context
    CGContextRef context = UIGraphicsGetCurrentContext();
    //Set the line color and width
    CGContextSetStrokeColorWithColor(context, [UIColor lightGrayColor].CGColor);
    CGContextSetLineWidth(context, 1.0f);
    //Start a new Path
    CGContextBeginPath(context);
    
    //Find the number of lines in our textView + add a bit more height to draw lines in the empty part of the view
    NSUInteger numberOfLines = (self.contentSize.height + self.bounds.size.height) / self.font.leading;
    
    //Set the line offset from the baseline. (I'm sure there's a concrete way to calculate this.)
    CGFloat baselineOffset = 6.0f;
    
    //iterate over numberOfLines and draw each line
    for (int x = 1; x < numberOfLines; x++) {
        //0.5f offset lines up line with pixel boundary
        CGContextMoveToPoint(context, self.bounds.origin.x + 10, self.font.leading*x + 0.5f + baselineOffset);
        CGContextAddLineToPoint(context, self.bounds.size.width - 10, self.font.leading*x + 0.5f + baselineOffset);
    }
    
    //Close our Path and Stroke (draw) it
    CGContextClosePath(context);
    CGContextStrokePath(context);
}

Here we need to calculate the number of lines before drawing. So, why are we adding contentsize.height and bounds.height. If we will use just the contentsize.height then:

1. We do not have any content initially and thus we will not have any line.
2. There won't be any lines at the bottom (after the content)

Thus, for a consistent and better view we will add textview's bounds.

UITableView basic tutorial

2013-03-15T12:33:00.000-07:00

In this tutorial we will create a table view with some dummy data, we will use disclosure indicator, change background color of cell, handle user selection, change separator color etc. There many tutorials which provides in depth information on UITableViews thus I will not touched that and instead targeted the practical How Tos.

Create a new single view project and add a UITableView to the initial view controller which has been added to the storyboard automatically.

In order to use UITableView in your viewcontroller you need to adapt to UITableViewDataSource and UITableViewDelegate.

UITableViewDelegate provides us with methods which let us handle user selection events, define row height, modifying view and much more.

UITableViewDataSource provides data to UITableView to construct the view (to render content). Create table view cells, define the number of sections, number of rows in sections and much more.

Adapt to required protocols

@interface AYViewController : UIViewController<UITableViewDataSource,UITableViewDelegate>

@end

Create dummy data

self.items = [[NSArray alloc] initWithObjects:@"First",@"Second",@"Third", nil];

Implement basic methods of the protocols we have adapted to

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return ((self.items && [self.items count] > 0) ? [self.items count]: 1);
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    static NSString *CellIdentifier = @"AYBasicSampleCellIdentifier";
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }
    
    cell.textLabel.text = [self.items objectAtIndex:indexPath.row];
    
    return cell;
}

Lets us run the application. BOOM!!!. I am not able to see anything in the table view. This is because we have not yet assigned a data source and delegate.

Assign DataSource and Delegate for UITableView

In order to perform this let us create an IBOutlet for our UITableView first. Now, let us assign data source and delegate.

self.sampleTableView.dataSource = self;
self.sampleTableView.delegate = self;

I have assigned them in viewDidLoad. Now, run your project again and now you will see dummy data on screen. WOW!!!

Its is working but we need to beautify it.

Add background color

In order to add background color add below mentioned code snippet in viewDidLoad.

self.sampleTableView.backgroundColor = [UIColor lightGrayColor];

Add round corner [Note: QuartzCore is needed for this]

Add QuarttzCore framework and then add QuartCore.h to the viewcontroller.

#import <QuartzCore/QuartzCore.h>

Now in viewDidLoad add following snippet.

self.sampleTableView.layer.cornerRadius = 10.0f;

Change separator color

In order to change separator color we need to use separatorColor property of UITableView.

self.sampleTableView.separatorColor = [UIColor grayColor];

Add a border to UITableView [Note: QuartzCore is needed for this]

self.sampleTableView.layer.borderColor = [UIColor grayColor].CGColor;
self.sampleTableView.layer.borderWidth = 1.0;

Change cell's text color

In order to change text color you need to update the cell creation code. We have created the cell in cellForRowAtIndex method. Use following snippet to change text color of cell.

cell.textLabel.textColor = [UIColor whiteColor];

Show Accessory Disclosure (Arrow at right)

In order to show accessory disclosure you need to set cell's accessoryType during cell creation in cellForRowAtIndex method.

cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

Change accessory disclosure color

By default accessory disclosure will have black color. In order to change the color of accessory disclosure you need to initialize accessory view with an image.

cell.accessoryView = [[UIImageView alloc]
                           initWithImage:[UIImage imageNamed:@"ArrowWhite.png"]];

Let us see how does our table view look now:

There is lot more to UITableView and in the next article in this series we will look into selection and navigating to different view controllers and more. Hope this post was of some help. Please share and provide your feedback.

Send Mail .NET

2012-12-15T21:23:00.002-08:00

Allowing user to send mail (feedback, contact etc) is a very common feature in current web applications. In this series of post we will talk about some basic mail features and how to implement them in c#.

Basics

In order to send mail we need SMTP server configured as mails work over SMTP. You can configure SMTP server yourself or if you are using web hosting services you can get an account setup for you. In order to receive mails we need POP. For this tutorial series we will use gmail SMTP server.

.NET APIs

.Net provides us with lots of classes present in System.Net.Mail to send an email. We will be using MailMessage, MailAddress and SmtpClient classes.

We will create a MailHelper and will use it in Winforms, Asp.Net, Console etc.

Mail Helper

using System.Collections.Generic;
using System.Net.Mail;

namespace MailConsole
{
    public class MailHelper
    {
        public static void SendMail(string subject,string message,List to)
        {
            var mailMessage = new MailMessage()
            {
                From = new MailAddress("YOUR-MAILID@gmail.com"),
                Subject = subject,
                Body = message
            };

            foreach (var id in to)
            {
                mailMessage.To.Add(id);
            }
            
            var smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.Port = 587;
            smtp.Credentials = new System.Net.NetworkCredential("YOUR-USERNAME", "YOUR-PASSWORD");
            smtp.EnableSsl = true;
            smtp.Send(mailMessage);
        }
    }
}

Knowing Singelton

2012-11-29T01:43:00.002-08:00

Singelton pattern in one of the most commonly used and talked about design pattern. Many appreciates it usefulness and many advocate against it. In this post we are not going to discuss all that but will concentrate on its implementation in c#.

Type:
It is a creational design pattern.

Intent:
It ensures that only one instance of the class exists.

Usage:
It is generally used when only one instance of a class is required. Thus, it can be seen to be used in logging frameworks, configuration objects etc.

The ownership of instance creation lies with the class itself. This is because we can not ensure that only one instance will ever exists for the class if the responsibility lies with someone else.

The class will instantiate the object when it will be used for the first time. This also ensures lazy initialization.

Point to consider:
Singelton object is mostly made accessible globally and thus being abused by being used as global variable. We must keep in mind that not only the singelton object but the whole object graph associated to it (which can be traversed through it) becomes global. Though most of us will say no to using global variables but will readily say yes to singeltons.

Simple Implementation:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PlayingWithSingelton
{
    public class SimpleSingelton
    {
        private static SimpleSingelton _instance;

        private SimpleSingelton()
        {
            
        }

        public static SimpleSingelton CurrentInstance
        {
            get
            {
                if(_instance == null)
                {
                    _instance = new SimpleSingelton();
                }
                return _instance;
            }
        }

        public void Print()
        {
            Console.WriteLine(this.GetHashCode());
        }
    }
}

In our SimpleSingelton class we have created a private constructor. This will ensure that no one else can instantiate SimpleSingelton by calling its constructor.

We have also create a private data member of type SimpleSingelton. This will hold the lone instance of SimpleSingelton. We have marked it static because we will access it from static members (property or method).

We have created a static property which will check if _instance is null or not. If it is null it will instantiate it and then return the _instance.

This implementation looks promising but it is not thread safe. In a multi-threaded scenario two threads can check for the nullability of _instance almost at the same time and thus can create two instances of SimpleSingelton as both will find _instance null.

Partially Thread Safe Implementation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace PlayingWithSingelton
{
    public class PartiallyThreadSafeSingelton
    {
        private static volatile PartiallyThreadSafeSingelton _instance;
        private static readonly Object Locker = new object();

        private PartiallyThreadSafeSingelton()
        {
            
        }

        public static PartiallyThreadSafeSingelton CurrentInstance
        {
            get
            {
                if(_instance == null)
                {
                    lock (Locker)
                    {
                        _instance = new PartiallyThreadSafeSingelton();
                    }
                }

                return _instance;

            }
        }
    }
}

In our PartiallyThreadSafeSingelton class we have marked the _instance as volatile this means that the most up-to date value of _instance will be used and the value will be requested every time we will use _instance although in the previous statements _instance value would have been retrieved.

In our getter for CurrentInstance we have use a lock. This will ensure that only one thread will create an instance at a time. Wait!!! But, multiple threads can check for nullability simulatneously and then one thread can wait for the other to create instance and release lock. Then it will also create an instance.

What if we check for nullability just before instantiating? Yes, we should.

Process intensive Thread Safe Implementation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PlayingWithSingelton
{
    public class ProcessIntensiveThreadSafeSingelton
    {
        private static volatile ProcessIntensiveThreadSafeSingelton _instance;
        private static readonly Object Locker = new object();

        private ProcessIntensiveThreadSafeSingelton()
        {
            
        }

        public static ProcessIntensiveThreadSafeSingelton CurrentInstance
        {
            get
            {
                lock (Locker)
                {
                    if (_instance == null)
                        _instance = new ProcessIntensiveThreadSafeSingelton();
                }
                return _instance;
                
            }
        }
    }
}

It is process intensive to acquire a lock every time. As the instantiation will happen only once. Thus we can change our implementation a bit and can check for nullability one more time but before acquiring lock.

Thread Safe Implementation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PlayingWithSingelton
{
    public class ThreadSafeSingelton
    {
        private static volatile ThreadSafeSingelton _instance;
        private static readonly Object Locker = new object();

        private ThreadSafeSingelton()
        {
            
        }

        public static ThreadSafeSingelton CurrentInstance
        {
            get
            {
                if (_instance == null)
                {
                    lock (Locker)
                    {
                        if (_instance == null)
                            _instance = new ThreadSafeSingelton();
                    }
                }
                return _instance;
                
            }
        }
    }
}

In future posts we will discuss more about singelton and its usage.

C# Polymorphism - handle with care

2012-11-04T00:17:00.002-07:00

Download

Overriding is the base for most of the design patterns which exists. It provides us with an essential tool called Polymorphism .

What is Polymorphism ?
Polymorphism means one interface and many forms. It is a characteristics of being able to assign a different meaning or usage to something in different contexts specifically to allow an entity such as a variable, a function or an object to have more than one form.

There are two types of Polymorphism.
Compile time: function or operator overloading
Runtime: Inheritence & virtual functions

Here, we are going to talk about the Runtime Polymorphism.

If you read the definition carefully you will see that there is going to be some type casting and compiler is going to made some assumptions. These assumptions may fail on execution. Let me explain this further.

Type casting:

There will be a parent interface (Interface, abstract class, class) and may be many child classes. These child classes will implement the polymorphic behavior in different ways. The consumer will use Parent class' variable and the reference can be changed at runtime.

Assumptions:

If we are using an interface and we cast an variable to that interface, compiler will assume that some child class of this variable's type will implement the methods specified by the interface. If this will not come out to be true it will throw exception at runtime.

using System;

namespace AbstractClasses
{
    class Program
    {
        static void Main(string[] args)
        {
            Apple fruit = new Apple();
            fruit.Print();
            IContract contract = (IContract) fruit;
            Console.ReadLine();
        }
    }

    internal interface IContract
    {
        void Display();
    }
    #region
    internal abstract class Fruit
    {
        public abstract string Name { get; set; }

        public virtual void Print()
        {
            Console.WriteLine("from abstract class");
        }
    }

    internal class Apple: Fruit
    {
        public override string Name { get; set; }

        public void Print()
        {
            Console.WriteLine("from child");
        }
    }
    #endregion
}

Handle With Care:

There are ways using which we can improve our code. Let us talk about them.

1. We can use 'as' keyword while casting a variable to an interface. This is because using the as operator is a better coding strategy than a straight cast because it yields a null on a conversion failure rather than raising an exception.

using System;

namespace AbstractClasses
{
    class Program
    {
        static void Main(string[] args)
        {
            Apple fruit = new Apple();
            fruit.Print();
            //IContract contract = (IContract) fruit; //Invalid cast exception

            IContract contract =  fruit as IContract;
            if(contract != null)
                contract.Display();
            Console.ReadLine();
        }
    }

    internal interface IContract
    {
        void Display();
    }
    #region
    internal abstract class Fruit
    {
        public abstract string Name { get; set; }

        public virtual void Print()
        {
            Console.WriteLine("from abstract class");
        }
    }

    internal class Apple: Fruit
    {
        public override string Name { get; set; }

        public void Print()
        {
            Console.WriteLine("from child");
        }
    }
    #endregion
}

2. We can use sealed keyword on classes which we do not want to be inherited. Then the compiler will not assume that the object being cast is going to exhibit polymorphic behavior and will check its cast to the interface at compile time.

using System;

namespace AbstractClasses
{
    class Program
    {
        static void Main(string[] args)
        {
            Apple fruit = new Apple();
            fruit.Print();
            
            IContract contract =  fruit as IContract;
            if(contract != null)
                contract.Display();
            Console.ReadLine();
        }
    }

    internal interface IContract
    {
        void Display();
    }
    #region
    internal abstract class Fruit
    {
        public abstract string Name { get; set; }

        public virtual void Print()
        {
            Console.WriteLine("from abstract class");
        }
    }

    internal sealed class Apple: Fruit
    {
        public override string Name { get; set; }

        public void Print()
        {
            Console.WriteLine("from child");
        }
    }
    #endregion
}

Compile Time Error:
Cannot convert type 'AbstractClasses.Apple' to 'AbstractClasses.IContract' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion.

c# reference types passed by value or reference

2012-11-03T22:43:00.000-07:00

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Time and again I have heard that in C#, method arguments are passed based upon there type. i.e. Value types are passed by value and reference types are passed by reference. This is so untrue. Reference types have nothing to do with pass by value.

Let us talk some basic. Consider the assignment first. When you assign a value type to another its value is copied. This is because value type variable contains its data directly. When you assign a reference type variable to another only the reference gets copied. This is because a reference type variable does not contains its data directly. It only holds reference to data.

Thus, when we pass a value type, its value gets copied and when we pass a reference type its reference gets copied. That is why if we change the value of a value type variable in the block (method), the change is not seen outside of it. On the other hand if we change the value of member of reference passed to the block from within the block the change persists outside the block.

Ok ! OK!

Some of you may say that, that is why reference types are passed by reference.

Wait! Wait!

Try changing the reference itself. You won't be able to do that. So actually you changed the value on the heap which was being pointed by the reference variable but you were not able to change the variable. Now, try using out or ref keywords and create a new reference type variable from within the block. You will succeed.

Actually when we are passing reference type without using out or ref we are passing just a pointer and that is why if we are trying to use new (to create a new object) we were not able to do that. On the other hand when we passed them using out or ref we passed pointer to pointer and that is why we were able to change the pointer being pointed using the new keyword.

Thus, we can safely say that in each case we changed the value being pointed by the reference and were not able to change the argument.

using System;
using System.Threading;

namespace ArgumentsPassByValue
{
    class Program
    {
        static void Main(string[] args)
        {
            Worker worker = new Worker();
            Request request = new Request();
            request.Id = 4;

            Console.WriteLine(request.Id + " : " + request.GetHashCode());

            worker.PassByReference(ref request);
            Console.WriteLine(request.Id + " : " + request.GetHashCode());

            //first request object will be collected as it is not being used
            GC.Collect();

            //forced thred to sleep so that you can see that first object has been 
            //collected and still we are using the variable request because it is pointing to some other location now.
            Thread.Sleep(1000);

            Console.WriteLine(request.Id + " : " + request.GetHashCode());
            Console.ReadLine();
        }
    }

    internal class Request
    {   
        public int Id { get; set; }

        ~Request()
        {
            Console.WriteLine(this.GetHashCode() + " : I am dying");
        }
    }

    internal class Worker
    {
        public void PassByReference(ref Request request)
        {
            request = new Request();
            request.Id = 6;
        }
        public void ValueChanger(Request request)
        {
            Console.WriteLine(request.Id + " : " + request.GetHashCode());
            request = new Request();
            request.Id = 6;
        }
    }
}

Some more references : http://msdn.microsoft.com/en-us/library/s6938f28.aspx

Callback in c#

2012-11-02T13:17:00.000-07:00

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Running tasks in background is the need of the hour when working on real world applications. There are few tasks which we can fire and forget but for few of them we will like to receive the feedback. This is when callbacks comes into the picture and provides a channel for these objects to communicate with each other.

These tasks are very common in desktop and mobile applications. In this post we will talk about callback mechanism in c#. In future post we will build upon this and do lot more.

Using interfaces for callbacks in c#

using System;
using System.Threading;

namespace Callbacks
{
    
    class Program
    {
        static void Main(string[] args)
        {
            var consumer = new Consumer();
            consumer.DoWork();
            Console.ReadLine();
        }
    }

    interface IOnProcessCompleteListener
    {
        void OnProcessComplete(string message);
    }

    internal class Consumer: IOnProcessCompleteListener
    {
        private Worker _worker;
        public Consumer()
        {
            _worker = new Worker();
            _worker.OnProcessCompleteListener = this;
        }

        public void DoWork()
        {
            Thread backgroundThread = new Thread(_worker.DoBackgroundWork);
            backgroundThread.Start();
            Console.WriteLine("Control is with main thread");
        }

        public void OnProcessComplete(string message)
        {
            Console.WriteLine(message);
        }
    }
    internal class Worker
    {
        public IOnProcessCompleteListener OnProcessCompleteListener;

        public void DoBackgroundWork()
        {
            Console.WriteLine("In worker");
            Thread.Sleep(1000);

            if(OnProcessCompleteListener != null)
                OnProcessCompleteListener.OnProcessComplete("Consumer has been called back");
        }

    }
}

Code is self explanatory and thus I will provide just a brief on it. We created an interface IOnProcessCompleteListener it has just one method. In the Worker class we have an data member which accepts an object of class which implements IOnProcessCompleteListener. This ensures that we can call OnProcessComplete method on this member once we are ready to call it back. The Consumer class will implement IOnPropertyChangeListener. Once Worker is done with stuff it will notify Consumer using the callback object. Just to simulate some background process I have made the worker thread to sleep before giving the call back.

Using Delegates to callback in c#

using System;
using System.Threading;

namespace CallBacksUsingDelegate
{
    class Program
    {
        static void Main(string[] args)
        {

            Listener listener = new Listener();
            listener.DoWork();
            Console.WriteLine("Now in main thread");
            Console.ReadLine();
        }
    }

    internal delegate void OnProcessComplete(string message);

    internal class Worker
    {
        public OnProcessComplete ProcessComplete;

        public void Process()
        {
            Console.WriteLine("Process: Running on " + Thread.CurrentThread.Name);
            Thread.Sleep(1000);
            if (ProcessComplete != null)
                ProcessComplete.Invoke("Process has completed");
        }
    }

    internal class Listener
    {
        private Worker _worker;
        public Listener()
        {
            _worker = new Worker();
            _worker.ProcessComplete = this.ProcessCompleteListener;
        }

        public void DoWork()
        {
            Thread backgroundThread = new Thread(_worker.Process);
            backgroundThread.Name = "Background Thread";
            backgroundThread.Start();
        }

        private void ProcessCompleteListener(string message)
        {
            Console.WriteLine(message);
        }
    }

}

In this case we have a delegate - OnProcessComplete. Class worker has an object of type OnProcessComplete and class Listener passes the callback function to the Worker wrapped in this delegate. Once the Worker is done with its stuff it invokes the delegate and passes the control back.

In the coming posts we will explore this power a bit more and try to do something more meaningful.

Your inputs are really important for me so please do provide them. Share it if you care :)

Android - Disable Text Selection

2012-10-24T10:15:00.000-07:00

In order to disable text selection in a WebView we can use following approaches:

CSS

* {

user-select: none;

-moz-user-select: -moz-none;

-khtml-user-select: none;

-webkit-user-select: none;

}

This approach will not work on all the versions of Android as the support was not there till late.

Handling LongClick

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
WebView webView = (WebView) this.findViewById(R.id.webView1);
webView.loadData("<html><head><style>head><body>You scored <b>192</b> points.</body></html>", "text/html", null);

webView.setOnLongClickListener(new View.OnLongClickListener() {

public boolean onLongClick(View v) {
return true;
}
});
}

Split String in C++ with delimiters

2012-10-21T21:00:00.001-07:00

In order to split string in c++ we can use strtok().

A sequence of calls to this function split str into tokens, which are sequences of contiguous characters separated by any of the characters that are part of delimiters.

On a first call, the function expects a C string as argument for str, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of last token as the new starting location for scanning. Read More Here

#include <iostream.h>

#include <string.h>

int main(int argc, char** argv)

{

// multiple delimiters can be provided

char const delimiters[] = "/:";

// initial string to split

std::string sCFIString = "/6/2702!/4/6/6/122/1:3";

// this pointer will point to the next word after every 'strtok' call

char *token = strtok(const_cast<char*>(sCFIString.c_str()), delimiters);

// if returned pointer is NULL, then there is no more words

while (0 != token)

{

puts(token); // print the word

token = strtok(NULL, delimiters); // move to the next one

}

return 0;

}

Output

2702!

122

Convert std::string to char* and const char* - c++

2012-10-20T22:16:00.000-07:00

Convert std::string to const char*

std::string name = "Anuj";

const char* constName = name.c_str();

Convert std::string to char*

std::string name = "Anuj";

const char* constName = name.c_str();

char *ptrToName = const_cast<char*>(name.c_str());

A simple progam

#include <iostream>

#include <stdio.h>

using namespace std;

int main()

{

std::string name = "Anuj";

const char* constName = name.c_str();

char *ptrToName = const_cast<char*>(name.c_str());

printf("%s",constName);

printf("%s",ptrToName);

cout << name << endl;

return 0;

}

Convert NSNumber to NSString

2012-08-19T23:53:00.000-07:00

In order to convert NSNumber to NSString you can use following method:

NSNumber *myNSNumber = [NSNumber numberWithInt:1];
NSString *myString = [myNSNumber stringValue];

Disable a hyperlink using javascript - jquery

2012-08-08T08:12:00.003-07:00

I was working on an iOS application where we were displaying HTML content. We did not have control over these HTMLs and because of these we were facing lots of issues. One of the issue was handling of hyperlinks, we needed to handle the navigation ourselves. You can disable the hyperlink using the preventDefault() javascript function. Below is the sample using which you can disable the default behavior of a hyperlink.

<html>

<head>
<script src="jquery-1.5.1.min.js" type="text/javascript"></script>
<style></style>
<script>
$(document).ready(function () {
$('a').click(function(e) {

e.preventDefault();
//do other stuff when a click happens
return false; //In few browsers you will need to return false at the end

});

});
</script>
</head>
<body>
<a href="www.google.com"> Google!!!</a>
</body>
</html>

Note: In few browsers you might have to return false at the end of the function.

Change selection background and color using css

2012-08-07T11:43:00.003-07:00

It is always nice to have a cool UI for our website. Changing the background and foreground color of selection can do wonders sometimes. In this post I will show you how you can achieve that. We can do this easily using CSS3. It provides us with ::selection selector. Safari supports ::selection and firefox supports ::-moz-selection. Webkit browsers supports ::-webkit-selection. With time many browsers have started supporting ::selection itself.

.content::selection
{
background: #E01624;
color:White;
}
.content::-moz-selection
{
background: #E01624;
color:White;
}

.content::-webkit-selection
{
background: #E01624;
color:White;
}
.content
{
overflow:hidden;
}

In HTML I have div with class as content.

How to get html tag name of an html element using jQuery

2012-08-03T12:22:00.001-07:00

Some times it is needed to get the tag name of an element. You can use below mentioned script to get that.

<html>

<head>

$(document).ready(function () {

alert($('#someElement').attr('tagName'));

)};

</script>

<body>

<a href="#">click to get tag name </a>

You want tag name of this element.

</div>

</body>

</html

Difference between typeof() and GetType in c#

2012-07-14T00:02:00.001-07:00

typeof() is used to get the type information from a type. Here type can be class, delegate, interface etc.

e.g. Type t = typeof(Employee);

GetType() is used to get the type information from the object.

e.g. var obj = new Employee();
Type t = obj.GetType();

Thus, when you have an object you should use GetType function to extract Type information and when you have only a type with you then you should use typeof() operator to extract type information.

Using Objective C files in C++ files (mm)

2012-06-12T20:05:00.002-07:00

If you're using .mm files (C++) in your project, when you include the header files in .mm files header you may get below mentioned error (Even though you have all the right linker flags set):

1. linker failed with exit code 1
2. directory not found

Solution:

1. Try adding the file to .mm file directly (not to .h file for .mm)
2. Try adding the file as extern
extern "C" {
#import "DetectDevice.h"
}

Inversion of control - Part 1

2012-06-05T11:08:00.003-07:00

When an object of a type depends on an object of another type we say that the types are coupled. This is because change in one can lead to a change in second. This will hamper the extensibility and modification in design. In a more complex system lot of classes interact with each other and this will lead to a very brittle design. Let's take an example:

class Program
{
static void Main(string[] args)
{
List<Employee> employees = new List<Employee>();
EmployeeController employeeController = new EmployeeController();
employees = employeeController.GetAllEmployees();
}
}

Program depends on EmployeeController to fetch Employee(s).

Inversion of control

Logically Inversion means rearrangement. As we have seen in the previous example that Program is controlling EmployeeController and this control is actually coupling them. Inversion of control is object-oriented practice via which we can decouple the classes by providing the implementation (EmployeeController) at runtime (instead of compile time) via abstraction.

This helps in following ways:-
1. Reduces the coupling in the system.
2. Makes sure that we "Program to an interface and not to the implementation".
3. Allows the implementation to be changed without impacting the consumer.
4. Every module can be developed independent of each other.
5. Allows a module to be a cohesive unit and concentrate on the responsibilities assigned to it.
6. Modules do not assume about the functioning of other modules but rely on the contract (Interface).

and many more.

Simpler explanation

Previous example assigns EmployeeController object statically to Program. In place of this IoC (inversion of control) uses an assembler to instantiate the object and assign it to the consumer. Even if we use an assembler Program still need to be aware of EmployeeController. Instead of this if we can make EmployeeController's contract available to Program it can delegate the task to the implementation (EmployeeCotroller) via it. In general Interfaces and (sometimes) abstract classes are used as the contract. Now the assembler assigns the EmployeeController object wrapped in the abstraction to Program and thus the implementation can change without impacting the consumer.

Dependency Injection

Dependency Injection is the mechanism using which we can assign the object to the consumer or we can achieve IoC by binding the objects at run time. We can also use Service Locator to provide IoC. We will discuss Service Locator in a future post.

Types of Dependency Injection

There are three common forms of dependency injection:
1. Constructor Injection
2. Setter Injection
3. Interface-based injection

We will discuss the implementation of DI in future posts.

We newbies and the application design and architecture

2012-05-06T00:10:00.002-07:00

After being around for some time in this world of IT I have started to realize why these experienced guys are so furious with the newbies. I use to read a lot of newbie bashing on web and use to think WTF. Now, I must say "Old is Gold".

There are three types of newbies I have come across. One who really do not want to design and just wants to get the job done in a procedural way. Second who know a thing or two about design and want to design there application the best possible way (constraint being there knowledge). Third who thinks they know everything about design and that is how things should be designed.

The real problem arises when they are working on an application from scratch. The first type may come up with a class or two and finish the code in a monolithic manner. The third type will create a design either too good or to brittle. These two types will surely get the work done even though extensibility and maintainability may not be there and thus the cost of every change will be just too high.

I have found the second type getting stuck more often then not. They are always circumspect about there design and some times they just think too much about it. They google for some hints and solutions (more often then not they find something). The problem is knowing whether the solution is right for there case or not.

I am not against any one type and neither I favor one. I put them down just so that one can realize where they fall. I have been lucky to get chance to work on an application or module design from scratch and some time on existing applications as well. Initially I found really difficult to move even an inch as I was two confuse about my design. I have been the second type and I have been the third.

Here are few of my learning's:

Never be the first type. You never know you might be the one working on the change tomorrow.
Design evolves. There is know best design. You can always better it gradually.
Follow the basic principles. Separation of concerns, Coupling, Cohesiveness are the few principles which I think if followed will always allow you to refactor your code latter.
Work in layers when needed.
You might be the best around (for the Third type) but may be you can learn from others mistake or can make them understand their mistake. Keep looking for the better solution or for the mistake you should not do yourself.
You might be technically very strong but you need to understand the needs of your customer then only you can design something good for the customer. You are not designing for yourself. You are designing for the customer. There is cost associated with whatever you do (do not spend too much at design) and obviously there will be cost associated with any change (do spend time on design).
There are simple techniques which when followed always allows you to improve latter. e.g. interface based programming, DI etc. Do the small things right and the rest will follow.
Do not hesitate in doing pair programming. You will always learn.

Most importantly do not just remain stuck. Start with something and realize the shortcomings and fix them. I am still learning and believe that we learn from our mistakes. I still believe I have spent too much time analyzing and trying to get the things right the first time (Being stuck). That said, please do invest lot of time at architectural design as module design can change comparatively easily and with less cost.

Learning C and or C++ on windows

2012-04-21T08:59:00.002-07:00

If you want to start learning C/C++ and still want to use windows, you can either use Microsofts Managed C++ with a great IDE (Visual Studio) or GNU C/C++ compilers.

Microsoft has invested a lot in C++ and Visual Studio. The powerful IDE really enhance the productivity. There is lot online documentation using which one can learn Microsoft's Managed C++ thick and fast. You can download Visual Studio Express for free and can start learning.

Download Visual Studio 2010 express from here. Learning resources.

If you want to learn GNU C / C++ you can start with downloading CodeBlocks. It is an IDE for GNU C / C++ and it comes bundled with the compiler which makes it really easy to install the compiler and avoid the complexities of getting the things in place pieces by pieces.

You can download CodeBlocks from here.

The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid

2012-04-07T20:24:00.000-07:00

It was 2 o'clock at night when I was creating a model (MVC) using Entity Framework. I thought of creating a UnitTest project to follow some TDD. When I tried to run my first TestMethod I got this vague exception. After investigating further with half closed eyes I found out, how dumb I was to not to include App.config in the test project.

Basic concept is pretty straight forward and logical. We generally add entity framework to a class library project in order to be able to reuse the library. The library project is not an executable in its own. Thus we need to add this project in some executable say a console App, windows App, ASP.NET or UnitTest. The runtime will then expect the executable to have a config associated with itself which will have the connection string, which entity framework library is looking for.

Thus, the solution is pretty simple. Add the app.config to the project you are trying to run or add connection string to the config if the project you are trying to run already have a config.

Also - It has been observed that in few cases &quot present in the connection string can cause similar problem. Try changing it to a single quote (').