Design Patterns in Java (Creational) - Singleton Pattern

Singleton Pattern

• Only one instance is created
• Lazily loaded

Design

• Static in nature
• Thread safe
• Private instance
• Private constructor

Simple Singleton

public class Singleton {

    

    private static Singleton singleton = new Singleton();

    

    private Singleton(){

    

    }

    

    public static Singleton getInstance(){

        return singleton;

    }

    

}

Lazy Load

public class Singleton {

    

    private static Singleton singleton = null;

    

    private Singleton(){

    

    }

    

    public static Singleton getInstance(){

        if(singleton == null){

            singleton = new Singleton();

        }

        return singleton;

    }

    

}

 +  Thread Safe

public static Singleton getInstance() {

        if (singleton == null) {

            synchronized (Singleton.class) {

                if (singleton == null) {

                    singleton = new Singleton();

                }

                

            }

        }

        return singleton;

    }