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Singleton Design Pattern
This example explores how to implement a SingletonPattern on a class in java.
 
 

Singleton Design Pattern

                         

This example explores how to implement a SingletonPattern on a class in java.

The Singleton design pattern ensures that only one instance of a class is created, it provides a global point of access to the object and allow multiple instances in the future without affecting a singleton class's clients. To ensure that only one instance of a class is created we make SingletonPattern as static. getInstance() method returns a single instance of the class. We create a private default constructor to avoid outside modification.

This example gets instances of SingletonPattern two times but the method getInstance() will return the same object without creating a new one.

 The code of the program is given below:

public class SingletonPattern{
  private static SingletonPattern instance;
  private SingletonPattern(){} 
public static synchronized SingletonPattern getInstance(){
  if (instance == null)
    {
    instance = new SingletonPattern();
    }
    return instance;
  }
public static void main(String arg[]){
      System.out.println("The output of two instance:");
    SingletonPattern sp=new SingletonPattern();
    System.out.println("First Instance: "+sp.getInstance());
    sp=new SingletonPattern();
    System.out.println("Second Instance:"+sp.getInstance());
  }
}

The output of the program is given below:

C:\rajesh\kodejava>javac SingletonPattern.java
C:\rajesh\kodejava>java SingletonPattern
The output of two instance:
First Instance: SingletonPattern@3e25a5
Second Instance:SingletonPattern@3e25a5

Download this example.

                         

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Current Comments

3 comments so far (
post your own) View All Comments Latest 10 Comments:

All examples are really very nice examples.
Thanx .....

Posted by amit k pathak on Saturday, 10.4.08 @ 14:43pm | #80889

Confusing:
SingletonPattern sp=new SingletonPattern(); is not visible outside this class.

Instead should be:
SingletonPattern sp = SingletonPattern.getInstance();

Posted by Patrick on Wednesday, 04.16.08 @ 10:07am | #56670

the document is veryv very helful

Posted by ashish on Tuesday, 02.12.08 @ 15:12pm | #48009

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