Singleton pattern: static or static final?

Question

It is better to declare the instance of a Singleton as static or as static final?

See the following example:

static version

public class Singleton {

    private static Singleton instance = new Singleton();

    private Singleton() {
    }

    public static Singleton getInstance() {
        return instance;
    }

}

static final version

public class Singleton {

    private static final Singleton INSTANCE = new Singleton();

    private Singleton() {
    }

    public static Singleton getInstance() {
        return INSTANCE;
    }

}

Answer 1

In your particular cases, there is no difference at all. And your second is already effectively final.

But

Keeping aside the fact that the below implementation is NOT thread safe, just showing the difference with respect to final.

In case of lazy initialization of your instance, you may feel the difference. Look lazy initialization.

public class Singleton {

    private static Singleton INSTANCE; /error

    private Singleton() {
    }

    public static Singleton getInstance() {
      if (INSTANCE ==null) {
         INSTANCE = new Singleton(); //error
      }
        return INSTANCE;
    }

}