Singleton Pattern

package com.exmpl.singleton;

public class PatternClass {

       // 1. create an object of PatternClass.

       private static PatternClass instance = new PatternClass();

       // 2. Create a private constructor, so that this class can not be

       // instantiated.

       private PatternClass() {

              // No argument constructor.

       }

       // 3. Create a getter method of "instance" property, which return instance

       // of "PatternClass".

       public static PatternClass getInstance() {

              return instance;

       }

       // Normal method.

       public void displayMessage() {

              System.out.println("I am displayMessage() under PatternClass.");

       }

}

package com.exmpl.singleton;

public class ClientClass {

       public static void main(String[] args) {

              /*

               * We can not create an instance of "PatternClass" as below, because of

               * private constructor. The following line will shown an compilation

               * error.

               */

              // PatternClass patternClass = new PatternClass();

              /*

               * Get the instance of "PatternClass", by calling "getInstance()"

               * method.

               */

              PatternClass patternClass = PatternClass.getInstance();

              // Now calling "displayMessage()" method.

              patternClass.displayMessage();

       }

}

Output è I am displayMessage() under PatternClass.