What is the singleton pattern in Java?

The Singleton pattern is one of the simplest design patterns in Java. This type of design pattern is a creation pattern because this pattern provides one of the best ways to create objects.                                                                                                                       (Recommended learning: java course )

This pattern involves a class that is responsible for creating an object while ensuring that only one object is created. This class provides a way to access its unique objects, which can be accessed directly without the need to instantiate an object of the class.

Implementation Example

We will create a single object class - SingleObject. The constructor of the SingleObject class is private and has its own static instance.

The SingleObject class provides a static method to obtain its static instance to the outside world. SingletonPatternDemo or sample class will use SingleObject class to get SingleObject object.

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

Get the unique object from the singleton class. SingletonPatternDemo.java

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();
   }
}

Step 3

Verify the output and get the following results -

Hello World!

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