设计模式之单例模式（懒汉式）

使用volatile的特性（保证可见性），实现单例模式

package com.dada.thread.threaddemo.chapter03;

/**
 * @author: dada
 * @date: 2020/12/17
 * @description: 单例模式
 */
public class SingleDemo {

    private static volatile SingleDemo instance = null;

    private SingleDemo(){
        System.out.println(Thread.currentThread().getName() + "\t 单例");
    }

    public static SingleDemo getInstance(){
        if (instance == null) {
            synchronized (SingleDemo.class){
                if (instance == null){
                    instance = new SingleDemo();
                }
            }
        }
        return instance;
    }

    public static void main(String[] args) {

        for (int i = 0; i < 10; i++) {
            new Thread(() ->{
                System.out.println(SingleDemo.getInstance() == SingleDemo.getInstance());
            } ).start();
        }

    }

}

输出：

Thread-0	 单例
true
true
true
true
true
true
true
true
true
true

Process finished with exit code 0