design pattern

Singleton Design Pattern

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Hi My friends, in this small tutorial we will discuss the Singleton design pattern and  I will show you an implementation in JAVA.

As you may already know  there are three types of design patterns: Creational, behavioral and structural. Singleton is among the creational patterns and it is the easiest one to learn.

Why Singleton? :

  • The need to have one and only instance of a class during the execution of the application.
  • The instance should not be accessible only from a method of the class.

Steps to implement the design :

  1. Make the constructor of the class that you want it to be singleton private.
  2. Create a public static method with return type of Class, this method will be responsible for the instantiation of the class.
  3. Add a private static attribute that represents the instance of the class .

The following code represents an implementation of this design pattern.

public class SingletonClass {

	private static  SingletonClass instance = null;
		
	// the constructor is private 
	private SingletonClass() {
		
	}
		
	// the method responsible for the instantiation 
	public static SingletonClass getInstance()
	{
		if(instance == null) {
			instance = new  SingletonClass();
		}
		return instance;
	}
	
	
}

public class TestSingletonClass {

	public static void main(String[] args) {
		
		//create the first instance 
		SingletonClass instance = SingletonClass.getInstance();
		
		System.out.println(instance);
		
		//create the second instance 
        SingletonClass instancetwo = SingletonClass.getInstance();
		
		System.out.println(instancetwo);
		
		// the outut of the two instances is the same . 
		
	}

}