How to write a Singleton in proper manner?

Question

Today in my interview one interviewer asked me to write a Singleton class. And i gave my answer as

public class Singleton {

    private static Singleton re         


        

Answer 1

This is because your solution is not threadsafe.

The modern way is to tie the instance to an enum value:

enum Singleton {
    INSTANCE;
}

If you want to use lazy init of the instance then you can use the ClassLoader to guarantee thread safety:

public class Singleton {
        private Singleton() { }

        private static class SingletonHolder { 
                public static final Singleton INSTANCE = new Singleton();
        }

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

More information on Wikipedia