double locked Singleton

How to write double locked Singleton class in Java ?

we can check double locked in java singleton class as below code

public class SingletonInstanceDemo {

    private static volatile SingletonInstanceDemo instance = null;

    // private constructor

    private SingletonInstanceDemo() {

    }

    public static SingletonInstanceDemo getInstance() {

        if (instance == null) {

            synchronized (SingletonInstanceDemo.class) {

                // Double check

                if (instance == null) {

                    instance = new SingletonInstanceDemo ();

                }

            }

        }

        return instance;

    }

}