Make an enum INSTANCE private

Question

I am using an enum singletom pattern like this:

public enum LicenseLoader implements ClientLicense {
    INSTANCE;

    /**
     * @return an instance of ClientLicense
     */
    public static ClientLicense getInstance() {
        return (ClientLicense)INSTANCE;
    }

   ...rest of code

}

Now I want to return the Interface and hide the fact that we are actually using an enum at all. I want the client to use getInstance() and not LicenseLoader.INSTANCE as one day I may decide to use a different pattern if necessary.

Is is possible to make INSTANCE private to the enum?

Answer 1

What about making a public interface and private enum that implements said interface, with a singleton INSTANCE constant?

So, something like this (all in one class for brevity):

public class PrivateEnum {

    public interface Worker {
        void doSomething();
    }

    static private enum Elvis implements Worker {
        INSTANCE;
        @Override public void doSomething() {
            System.out.println("Thank you! Thank you very much!");
        }
    }

    public Worker getWorker() {
        return Elvis.INSTANCE;
    }
}

This way, you're not exposing Elvis.INSTANCE (or even enum Elvis at all), using an interface to define your functionality, hiding all implementation details.

Answer 2

All enum constants are accessible. For instance through deserialisation or the enum-specific reflective methods.

As always, I strongly suggest avoiding singletons.