单例模式详解-优快云博客

本文链接：https://blog.youkuaiyun.com/lujia_loney/article/details/77021901

本文介绍了单例模式的三种实现方式：饿汉式、懒汉式和静态内部类方式。饿汉式简单但不能延迟加载；懒汉式支持延迟加载，但需注意多线程安全问题；静态内部类方式既实现了延迟加载又保证了线程安全。

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单例模式是我们经常用的设计模式之一，下面记一下几种常用的单例模式的写法，方便自己查阅

1.饿汉单例模式--缺点就是不能延迟加载

class SingltonDemoOne{
    private static SingltonDemoOne singltonDemoOne=new SingltonDemoOne();
    private SingltonDemoOne() {
    }
    public static SingltonDemoOne getSingltonDemoOne(){
        return singltonDemoOne;
    }

}

2.懒汉单例模式--懒加载

class SingltonDemoTwo{
        private static SingltonDemoTwo singltonDemoTwo;
        private SingltonDemoTwo(){
    
        }
        public static SingltonDemoTwo getSingltonDemoTwo(){
            if(singltonDemoTwo==null){
                singltonDemoTwo=new SingltonDemoTwo();
            }
            return singltonDemoTwo;
        }
    }

上面的虽然实现了懒加载，但并不适用语多线程下，修改加上syncihronized

class SingltonDemoTwo{
        private static volatile SingltonDemoTwo singltonDemoTwo;
        private SingltonDemoTwo(){

        }
        public static  SingltonDemoTwo getSingltonDemoTwo(){
            if(singltonDemoTwo==null){
                synchronized (SingltonDemoTwo.class){
                    if (singltonDemoTwo==null){
                        singltonDemoTwo=new SingltonDemoTwo();

                    }
                }
            }
            return singltonDemoTwo;
        }
    }

3.使用静态内部类

class SingletonDemoThree{
    private static class Inner{
        public static SingletonDemoThree singletonDemoThree=new SingletonDemoThree();
    }
    private SingletonDemoThree (){

    }
    public SingletonDemoThree getSingleton(){
        return Inner.singletonDemoThree;
    }
}

java--几种单例式