Singleton Design Pattern

Rules :

  1. Constructor should be private.
  2. Private Static object of self should be declared in the class.
  3. This object should be initialized in a getInstance method

Example :

public class SingletonDemo {
	private static SingletonDemo obj; //1. Make a object of self private and static
	private SingletonDemo(){ //2. create a private constructor
	public static SingletonDemo getInstance() { //3. create a static method that returns the instantiated method
		if(obj==null) {
			obj = new SingletonDemo();
		return obj;

What are the difference between a static class and a singleton class?

  • A static class can not be a top level class and can not implement interfaces where a singleton class can.
  • All members of a static class are static but for a Singleton class it is not a requirement.
  • A static class get initialized when it is loaded so it can not be lazily loaded where a singleton class can be lazily loaded.
  • A static class object is stored in stack whereas singlton class object is stored in heap memory space.

How to prevent cloning of a singleton object?

Throw exception within the body of clone() method

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