As of release 1.5, there is a third approach to implementing singletons. Simply make an enum type with one element:

// Enum singleton – the preferred approach

public enum Elvis {

INSTANCE;

public void leaveTheBuilding() { … }

}

This approach is functionally equivalent to the public field approach, except that it is more concise, provides the serialization machinery for free, and provides an ironclad guarantee against multiple instantiation, even in the face of sophisticated serialization or reflection attacks. While this approach has yet to be widely adopted, a single-element enum type is the best way to implement a singleton.

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