单例模式

 做些笔记。

引用https://blog.csdn.net/weixin_40834464/article/details/82958187

//单例模式
public class SingleTon {

    //私有得构造方法
    private SingleTon(){}

    //饿汉 类加载的时候就加载完成
    private static final SingleTon singleTon = new SingleTon();

    //
    public static SingleTon getSingleTon(){
        return singleTon;
    }

}

//双重校验锁
public class SingleTon2 {

    private SingleTon2(){};

    //同步机制
    //volatile 禁止指令重排序
    private volatile static SingleTon2 singleTon2=null;

    //双重校验锁先判断 uniqueInstance 是否已经被实例化，如果没有被实例化，那么才对实例化语句进行加锁
    public static SingleTon2 getSingleTon2() {
        if(singleTon2==null){
            synchronized(SingleTon2.class){
                if (singleTon2==null) {
                    singleTon2 = new SingleTon2();
                }
            }
        }
        return singleTon2;
    }

    //对整个方法都加锁，同时只有一个线程能访问，
//    public static synchronized SingleTon2 getInstance(){
//        if (singleTon2==null){
//            singleTon2 = new SingleTon2();
//        }
//        return singleTon2;
//    }
}

/**
 * 静态内部类写法
 */
public class SingleTon3 {
    private  SingleTon3(){};

    //方问静态内部类时 才实例化SingleTon3
    private static class SingleTonHolder{
        private static final SingleTon3 singleTon3 = new SingleTon3();
    }

    public static SingleTon3 getSingleTon3(){
        return SingleTonHolder.singleTon3;
    }
}

/**
 *枚举类singleTon
 */
public class EnumSingleton {

    private EnumSingleton(){};

    public static EnumSingleton getEnumSingleTon(){
        return SingleTon4.INSTANCE.getSingleTon();
    }


    private static enum SingleTon4{

        INSTANCE;

        private  EnumSingleton singleTon;
        private SingleTon4(){
            singleTon = new EnumSingleton();
        };

        public EnumSingleton getSingleTon(){
            return singleTon;
        }

    }

    public static void main(String[] args) {
        EnumSingleton enumSingleton1 = EnumSingleton.getEnumSingleTon();
        EnumSingleton enumSingleton2 = EnumSingleton.getEnumSingleTon();
        System.out.println("enumSingleTon1 = enumSingleTon2?"+(enumSingleton1 == enumSingleton2));
    }

}

 

标签：EnumSingleton,private,static,模式,单例,singleTon2,SingleTon2,public
来源： https://blog.csdn.net/qq_39249471/article/details/110680049