The best singleton pattern since Java 5

问题:

Since Java 5 it is said that the best way to create a singleton is by a single-element enum type.

Example:

public enum SuperSingleton implements Zooma{
    INSTANCE;

    /**
     */
    public void fightTheBattle(){
        System.out.println("I am fighting the battle!!!");
    }

    @Override
    public void runningWild() {
        //This is method implemented from the Zooma interface.      
    }
}

According to Joshua Bloch, the single-element enum type singleton is;

• more concise
• provides the serialization machinery for free
• and provides an ironclad against multiple instantiation.

I can see how it is more concise and how it provides an ironclad against multiple instantiation, but how does it provide the serialization machinery for free?

Is it something the singleton gets by being an enum?

回答1:

Yes, Enums are all extended off of the Enum class, which implements Serializable.

回答2:

I'm not 100% sure, but I think if you deserialize a serialized singleton more then once you might end up with more than one instance. An enum instance will always stay a singleton.

So you get 'more serialization' then what you get from just implementing serialization.

回答3:

http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Enum.html

yes :)