41.单例模式

单例模式

一、饿汉式

class Test {

    private static Test test = new Test();

    private Test() {
        System.out.println("Test ");
    }

    public static Test getTest() {
        return test;
    }
}

二、懒汉式

public class Singleton {
    private static volatile Singleton singleton = null;
 
    private Singleton(){}
 
    public static Singleton getSingleton(){
        if(singleton == null){
            synchronized (Singleton.class){
                if(singleton == null){
                    singleton = new Singleton();
                }
            }
        }
        return singleton;
    }    
}

三、登记者模式【最牛逼的写法、推荐使用】

/**
 * 最牛逼的单利模式
 */
class Singleton {

    private Singleton() {}

    public static Singleton getInstance() {
        return Holder.SINGLETON;
    }

    private static class Holder {
        public static final Singleton SINGLETON = new Singleton();
    }
}