Singleton design pattern in Java

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

        Singleton x = Singleton.getInstance();
        Singleton y = Singleton.getInstance();
        
        System.out.println("The same objects: " + (x == y)); // true
    }
}

class Singleton {

    private Singleton(){};
    private static Singleton INSTANCE = new Singleton();

    public static Singleton getInstance() {
        return INSTANCE;
    }
}

 

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• Interviewer: Go with Lazy initialization.

class Singleton {

    private Singleton(){};
    private static Singleton INSTANCE;

    public static Singleton getInstance() {
        if (INSTANCE == null)
            INSTANCE = new Singleton();        
        return INSTANCE;
    }
}

 

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• Interviewer: Support multi-threading.

class Singleton {

    private Singleton(){};
    private static Singleton INSTANCE;

    public static Singleton getInstance() {

        if (INSTANCE == null) {
            synchronized (Singleton.class) {
                if (INSTANCE == null)
                    INSTANCE = new Singleton();
            }
        }
        return INSTANCE;
    }
}