Enum version of singleton: How to implement and its advantages?

Question

    Public class Singleton{

             //private static ref
             private Static Singleton uniqueInstance; 

              //private constructor
              private Singleton(){
              }

             public static Singleton getInstance{

             if(uniqueInstance==null){

            uniqueInstance= new Singleton();
             }

           return uniqueInstance;

           }

}

The above class is my current implementation of the traditional use of singleton. How would I implement the enum version of singleton on this class? And what are its benefits over the traditional?

I.e. how does this work:

public enum Foo {
   INSTANCE;
}

Take a moment to see if the question has been asked before; you'll save yourself and us time. — Jeroen Vannevel, May 04 '14 at 15:34
Your solution is not thread-safe, not guaranteed to be singleton when you have multiple threads. — Ishtar, May 04 '14 at 15:40

score 0 · Answer 1 · answered May 04 '14 at 15:46

As per Joshua Bloch Creating a sigleton using enum is guaranteed way that a class be singleton. And even using reflection multiple instances cannot be created. But some people don't like to implement sigletons this way. and it's topic of debate.

By the way the code snippet you have is not thread safe. More than one threads can go into getInstance method at the same time and your sigleton pattern will break. If you need more explanation how let me know in the comments.

See this link it explains with code how your sigleton pattern can break if it's not implemented as enum.

Enum version of singleton: How to implement and its advantages?

1 Answers1