enum实现的单例？（同时满足懒汉的懒加载和恶汉的线程安全）

enum实现的单例是effective java中比较推荐的做法

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上代码

public class enumSingleton {
   private static boolean flag = true;

    private enumSingleton() {
        synchronized (enumSingleton.class) {
            if (flag) {
                flag = !flag;
            }else{
                throw new Error("单例模式被侵犯！");
            }
        }
    }

    public static enumSingleton getInstance(){
        return singleEnum.SINGLETON.getInstance();
    }


    private enum singleEnum{
        SINGLETON;

        private enumSingleton singleton;

        //jvm保证枚举的构造方法只被调用一次
        singleEnum(){
            singleton = new enumSingleton();
        }

        private enumSingleton getInstance(){
            return singleton;
        }
    }
}

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简单测试一波