Answer / hardeep thakur

Here is code to implement the singleton

public class SingletonClass {
private static SingletonClass singleObj ;
private SingletonClass(){}

public static synchronized SingletonClass getInstance()
{
if(singleObj ==null){
singleObj = new SingletonClass();
}
return singleObj;
}

public Object clone() throws CloneNotSupportedException
{
throw new CloneNotSupportedException();
}

}

Answer / ajooba

since 1.5 version best way is to use an enum

public enum My
{
instance;
}

Answer / supraja

The Singleton pattern
In Design Patterns, the authors describe the Singleton
pattern like this:

Ensure a class has only one instance, and provide a global
point of access to it.



The figure below illustrates the Singleton design pattern
class diagram.



Singleton class diagram

As you can see from the figure above, there's not a whole
lot to the Singleton design pattern. Singletons maintain a
static reference to the sole singleton instance and return
a reference to that instance from a static instance()
method.

Answer / dara

Ensure a class has only one instance, and provide a global
point of access to it. Singletons maintain a static
reference to the sole singleton instance and return a
reference to that instance from a static instance() method.

Example:
========

public class MyClassSingleton {

private static MyClassSingleton instance;

//Constructor must be protected or private to perevent
creating new object
protected MyClassSingleton() {

}
//could be synchronized
public static MyClassSingletongetInstance() {
if (instance==null)
instance = new MyClassSingleton()
return instance;

}
public void method1(){
System.out.println("hello singleton");
}
}//end of class

Answer / manoj kumar

public class DateUtil implements Serializable,Cloneable {

   private static volatile Dateutil instance;

   private DateUtil() {
     //no-op
   }

   public static DateUtil getInstance() {

      if(instance==null) {
        synchronized(DateUtil.this) {
           if(instance==null) {
              instance = new DateUtil();
           }
        }
        return instance;
      }
   
   protected Object readResolve() {
     return instance;
   }

   public Object clone() throws CloneNotSupportedException {

     super.clone();

     throw new CloneNotSupportedException;
  }

Answer / shaik baji

Singleton Example:
==================
public class Singleton
{
private static Singleton singleton;

private Singleton()
{
}

public static Singleton getInstance()
{
if(singleton==null)
{
singleton = new Singleton();
return singleton;

}
else
{
return singleton;
}

}

}


Accessing Singleton instance
============================
public class STDemo
{
public static void main(String[] args)
{
Singleton obj1= Singleton.getInstance();
System.out.println(obj1.hashCode());

Singleton obj2= Singleton.getInstance();
System.out.println(obj2.hashCode());

Singleton obj3= Singleton.getInstance();
System.out.println(obj3.hashCode());

}
}

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