thread safe singleton using enum

Question

I am not able to understand how Enum can be used for thread safe singleton instantiation. So let us say I have a class A which I want to make singleton. How do I do that using Enum ? I came across suggestion like the code below, but not really able to understand. In the below shall I replace INSTANCE with A singleObj = new A(); ?

Moreover, how exactly should class A look like as in what thing should I take care of there .. for example: making constructor private etc.

public enum EasySingleton{
    INSTANCE;
}

Answer 1

In the below shall I replace INSTANCE with A singleObj = new A(); ?

You don't. You use:

EasySingleton instance = EasySingleton.INSTANCE;

You write the singleton just like a normal class, with whatever methods you want etc - but no public constructors (which aren't valid in enums anyway).

Answer 2

As Jon mentioned you would do the following:

EasySingleton instance = EasySingleton.INSTANCE;
instance.doSomething();

If you need some further examples, as well as pros/cons to many of the approaches to creating Singleton classes you can visit: http://avaldes.com/creating-a-thread-safe-singleton-class-with-examples/ .