Singleton Design Pattern

Singleton Design Pattern
(Creational Design Pattern)

Singleton design pattern is the simplest design pattern we can found. It allows only to create only one instance at a time from the given class.

e.g. clipboard in windows and mobile devices

A singleton class,

• Should be a private class
• provides a global access point to the class (private static)

Class diagram

Implementation

Create a simple java application and create following class
Singleton.class

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public class Singleton { //create global access point private static Singleton firstInstance = null; String clipboard = ""; //keep the constructor private private Singleton(){ } //add synchronized to avoid multiple accesses in multithread environments public static synchronized Singleton getInstance(String text){ if(firstInstance == null){ firstInstance = new Singleton(); //firstInstance.clipboard = text; } firstInstance.clipboard = text; return firstInstance; } }

SingletonTestDemo.java

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public class SingletonTestDemo { /** * @param args the command line arguments */ public static void main(String[] args) { Singleton instance = Singleton.getInstance("first copy text"); System.out.println("1st instance ID: " + System.identityHashCode(instance)); System.out.println(instance.clipboard + "\n"); Singleton instance2 = Singleton.getInstance("second copy text"); System.out.println("2nd instance ID: " + System.identityHashCode(instance2)); System.out.println(instance2.clipboard + "\n"); } }

Now test the application
output:

Download source code (GitHub): Click here