Singleton Design Pattern

This pattern involves a single class which is responsible to create an object while making sure that only single object gets created.

This class provides a way to access its only object which can be accessed directly without need to instantiate the object of the class.

This type of design pattern comes under creational pattern

 

 

Code example:

Step 1.

Create a Singleton Class.

SingleObject.java

public class SingleObject {

   //create an object of SingleObject
   private static SingleObject instance = new SingleObject();

   //make the constructor private so that this class cannot be
   //instantiated
   private SingleObject(){}

   //Get the only object available
   public static SingleObject getInstance(){
      return instance;
   }

   public void showMessage(){
      System.out.println("Hello World!");
   }
}

 

Step 2. SingletonPatternDemo.java

Get the only object from the singleton class.

public class SingletonPatternDemo {
   public static void main(String[] args) {

      //illegal construct
      //Compile Time Error: The constructor SingleObject() is not visible
      //SingleObject object = new SingleObject();

      //Get the only object available
      SingleObject object = SingleObject.getInstance();

      //show the message
      object.showMessage();
   }
}