Java

What is Singleton Design Pattern?

Singleton is a design pattern that ensures that a class can only have one object.

Singleton Class Using Eager Initialization Method

  
	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class SingletonExample {
	
		// Instance will be created at load time
		private static SingletonExample singletonExample = new SingletonExample();
	
		// Creating private constructor
		private SingletonExample() {
		}
	
		// Declaring static method
		public static SingletonExample getInstance() {
			return singletonExample;
		}
	}
	

Test above SingletonExample here.

	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class Main {
	
		public static void main(String[] args) {
	
			SingletonExample singletonExampleObject1 = SingletonExample.getInstance();
			SingletonExample singletonExampleObject2 = SingletonExample.getInstance();
			SingletonExample singletonExampleObject3 = SingletonExample.getInstance();
	
			// We will check here above created objects are equal or not
			if (singletonExampleObject1 == singletonExampleObject2 && singletonExampleObject2 == singletonExampleObject3) {
				System.out.println("Objects are same.");
			} else {
				System.out.println("Objects are different.");
			}
		}
	}
	

Singleton Class Using Lagy Initialization Method

  
	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class SingletonUsingLazyInitialization {
	
		// Declaring Static variable reference
		private static SingletonUsingLazyInitialization singletonUsingLazyInitialization = null;
	
		// Creating private constructor
		private SingletonUsingLazyInitialization() {
		}
	
		// Declaring static method
		public static SingletonUsingLazyInitialization getInstance() {
			if(singletonUsingLazyInitialization == null) {
				return singletonUsingLazyInitialization = new SingletonUsingLazyInitialization();
			}
			return singletonUsingLazyInitialization;
		}
	}

Test above Singleton Using Lazy Initialization Example here.

	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class SingletonUsingLazyInitializationMain {
	
		public static void main(String[] args) {
			SingletonUsingLazyInitialization object1 = SingletonUsingLazyInitialization.getInstance();
			SingletonUsingLazyInitialization object2 = SingletonUsingLazyInitialization.getInstance();
			SingletonUsingLazyInitialization object3 = SingletonUsingLazyInitialization.getInstance();
	
			// We will check here above created objects are equal or not
			if (object1 == object2 && object2 == object3) {
				System.out.println("Objects are same.");
			} else {
				System.out.println("Objects are different.");
			}
		}
	}

	

Singleton Class Using Thread Safe Method

  
	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class SingletonUsingThreadSafe {
	
		// Declaring Static variable reference
		private static SingletonUsingThreadSafe singletonUsingThreadSafe = null;
	
		// Creating private constructor
		private SingletonUsingThreadSafe() {
		}
	
		// Declaring static synchronized method
		public static synchronized SingletonUsingThreadSafe getInstance() {
			if(singletonUsingThreadSafe == null) {
				return singletonUsingThreadSafe = new SingletonUsingThreadSafe();
			}
			return singletonUsingThreadSafe;
		}
	}

Test above Singleton Using Thread Safe Example here.

	package com.hareeshsoni.singletonexample;
	
	/**
	 * @author HAREESH
	 *
	 */
	public class SingletonUsingThreadSafeMain {
	
		public static void main(String[] args) {
			SingletonUsingThreadSafe object1 = SingletonUsingThreadSafe.getInstance();
			SingletonUsingThreadSafe object2 = SingletonUsingThreadSafe.getInstance();
			SingletonUsingThreadSafe object3 = SingletonUsingThreadSafe.getInstance();
	
			// We will check here above created objects are equal or not
			if (object1 == object2 && object2 == object3) {
				System.out.println("Objects are same.");
			} else {
				System.out.println("Objects are different.");
			}
		}
	}