单例模式

枚举能够防止单例被反射破坏,其他的不能

饿汉模式

public static class Hungry{
        private Hungry(){}
        private final static Hungry hungry = new Hungry();
        public static Hungry getInstance(){
            return hungry;
        }
    }

普通的懒汉模式

public static class Lazy{
        private Lazy(){}
        private static Lazy lazy;
        public static Lazy getInstance(){
            if (lazy==null){
                lazy=new Lazy();
            }
            return lazy;
        }
    }

DCL懒汉模式

public static class LazyMan{
        private LazyMan(){}
        private static volatile LazyMan lazyMan;
        public static LazyMan getInstance(){
            if (lazyMan==null){
                synchronized (LazyMan.class){
                    if (lazyMan==null){
                        lazyMan=new LazyMan();
                    }
                }
            }
            return lazyMan;
        }
    }

静态内部类

public static class Holder{
        private Holder(){}
        private static class Inner{
            private static final Holder holder = new Holder();
        }
        public static Holder getInstance(){
            return Inner.holder;
        }
    }

枚举

//能够防止单例被反射破坏
public static enum EnumSingleton{
        //测试用例
        INSTANCE1, INSTANCE2,INSTANCE3;
        public static EnumSingleton getInstance(){
            return INSTANCE2;
        }
    }