public enum SingleTon {

    INSTANCE;

    public void speak() {

        System.out.println(this + " is speaking! ");

    }

}  

public class SingleTonTest {  

    public static void main(String[] args) throws Exception {

        SingleTon s1 = SingleTon.INSTANCE;

        s1.speak();

        SingleTon s2 = SingleTon.INSTANCE;

        s2.speak();

        System.out.println(s1 == s2);

    }

}  

测试结果：

INSTANCE is speaking!

INSTANCE is speaking!

true