Create immutable class

/**
 * Create Immutable Class
 * 
 * @author:http://javainterviewprograms.blogspot.in/
 * 
 */
public final class ImmutableClass {

 private final String name;

 public ImmutableClass(String name)

 {

  this.name=name;

 }

 public String getName()

 {

  return name;

 }

}

To make class immutable :

1.instance variable final

2.class final

3.No setter method

Thread Dead lock solution ?

package com.JavaInterview.Programs;

/** * 
 * @author:http://javainterviewprograms.blogspot.in/
 * 
 */

public class DeadlockSolution {

 public static Object lock1 = new Object();

 public static Object lock2 = new Object();

 public static void main(String args[]) {

  Thread1 t1 = new Thread1();

  Thread2 t2 = new Thread2();

  t1.start();

  t2.start();

 }

 private static class Thread1 extends Thread {

  public void run() {

   synchronized (lock1) {

    System.out.println("Thread 1 :holding the lock1 ...");

    try {

     Thread.sleep(10);

    } catch (InterruptedException e) {

    }

    System.out.println("Thread 1 :waiting for lock 2....");

    synchronized (lock2) {

     System.out.println("Thread 1: holding lock1 and 2...");

    }

   }

  }

 }

 private static class Thread2 extends Thread {

  public void run() {

   synchronized (lock1) // to create deadlock use lock2 here

   /*

    * By interchanging locks position we have avoided deadlock

    * here(From creating deadlock example)

    */

   {

    System.out.println("Thread 2 :holding the lock2");

    try {

     Thread.sleep(20);

    } catch (InterruptedException e) {

    }

    System.out.println("Thread 2 : waiting for lock2 ...");

    synchronized (lock2)// to create deadlock use lock1 here

    {

     System.out.println("Thread 2 : holding both lock1 and 2..");

    }

   }

  }

 }

}

Output:

Thread 1 :holding the lock1 ...

Thread 1 :waiting for lock 2....

Thread 1: holding lock1 and 2...

Thread 2 :holding the lock2

Thread 2 : waiting for lock2 ...

Thread 2 : holding both lock1 and 2..

Create Thread dead lock ?

package com.JavaInterview.Programs;
/**
 * Find Out Factorial of a number
 * 
 * @author:http://javainterviewprograms.blogspot.in/
 * 
 */

public class ThreadDeadlock {

 public static Object lock1 = new Object();

 public static Object lock2 = new Object();

 public static void main(String args[]) {

  Thread1 t1 = new Thread1();

  Thread2 t2 = new Thread2();

  t1.start();

  t2.start();

 }

 private static class Thread1 extends Thread {

  public void run() {

   synchronized (lock1) {

    System.out.println("Thread 1 :holding the lock1 ...");

    try {

     Thread.sleep(10);

    } catch (InterruptedException e) {

    }

    System.out.println("Thread 1 :waiting for lock 2....");

    synchronized (lock2) {

     System.out.println("Thread 1: holding lock1 and 2...");

    }

   }

  }

 }

 private static class Thread2 extends Thread {

  public void run() {

   synchronized (lock2) {

    System.out.println("Thread 2 :holding the lock2");

    try {

     Thread.sleep(20);

    } catch (InterruptedException e) {

    }

    System.out.println("Thread 2 : waiting for lock1 ...");

    synchronized (lock1) {

     System.out.println("Thread 2 : holding both lock1 and 2..");

    }

   }

  }

 }

}

Output :

Thread 2 :holding the lock2

Thread 1 :holding the lock1 ...

Thread 1 :waiting for lock 2....

Thread 2 : waiting for lock1.

...

Basic HashSet Operations -Adding elements ,adding duplicates ,removal?

package com.JavaInterview.Programs;

import java.util.HashMap;

import java.util.HashSet;

/*

 * @author:http://javainterviewprograms.blogspot.in/

 * 

 */

public class HashsetTest {

 

 public static void main (String args[])

 {

  HashSet<String> h= new HashSet<String>();

 

 

  h.add("abc");

  h.add("bcd");

 

  System.out.println("hashset sample"+h);

 

  //adding duplicates object

  h.add("abc");

  System.out.println("After adding duplicates key"+h);

 

  //HashSet  size

  System.out.println("HashSet size "+h.size());

 

  //remove elements

  h.remove("abc");

  System.out.println("After removal "+h);

 }

}

Output:

hashset sample[abc, bcd]

After adding duplicates key[abc, bcd]

HashSet size 2

After removal [bcd]

Write HashMap Programme to display basic functionaliy -After adding duplicate keys ,remove etc?

package com.JavaInterview.Programs;

import java.util.*;

/**
 * Find Out Factorial of a number
 * 
 * @author:http://javainterviewprograms.blogspot.in/
 * 
 */

public class HashmapTest {

 public static void main (String args[])

 {

  HashMap String,Integer> h= new HashMap String,Integer>();

 

  /*HashMap String,int> h= new HashMap String,int>();compiler error |You can't use

  primitive types as generic arguments in Java*/

  h.put("abc",12);

  h.put("bcd", 13);

 

  System.out.println("hashmap sample"+h);

 

  //adding duplicates keys

  h.put("abc",14);

  System.out.println("After adding duplicates key"+h);

 

  //adding duplicates value

  h.put("cdf",13);

  System.out.println("After adding duplicates value"+h);

 

  //adding duplicates keys again

  h.put("abc",15);

  System.out.println("Again after adding duplicates key"+h);

 

  //fetch by key

  System.out.println("Fetch map by its value"+h.get("abc"));

  System.out.println("Fetch map by its value"+h.get("bcd"));

 

  //HashMap Empty

  System.out.println("Is HashMap empty "+h.isEmpty());

 

  //remove elements

  h.remove("abc");

  System.out.println("After removal "+h);

 }

}

Output :

hashmap sample{abc=12, bcd=13}

After adding duplicates key{abc=14, bcd=13}

After adding duplicates value{abc=14, bcd=13, cdf=13}

Again after adding duplicates key{abc=15, bcd=13, cdf=13}

Fetch map by its value15

Fetch map by its value13

Is HashMap empty false

After removal {bcd=13, cdf=13}

Write a Singleton Example -Thread Safe ?

/*Singelton Example using Double checked (Thread Safe)*/

public class MySingleton {

 private static volatile MySingleton obj;

 //private constructor

 private MySingleton()

 {

 

 }

 //Instance method

    public static MySingleton getInstance()

    {

     if(obj==null)  //single checked

     {

      synchronized(MySingleton.class)

      {

       if(obj==null) //double checked

       {

          obj=new MySingleton();

          }

      }

     }

     return obj;

    }

    

    public void print()

    {

     System.out.println("this is my Singleton Example");

    }

    

    public void main(String args[])

    {

     MySingleton m=MySingleton.getInstance();

     m.print();

    }

}