public class EnumSingleton{
private EnumSingleton(){}
public static EnumSingleton getInstance(){
return Singleton.INSTANCE.getInstance();
}

private static enum Singleton{
INSTANCE;

private EnumSingleton singleton;
//JVM会保证此方法绝对只调用一次
private Singleton(){
singleton = new EnumSingleton();
}
public EnumSingleton getInstance(){
return singleton;
}
}
}