volatile关键字的介绍

import java.util.concurrent.TimeUnit;


public class VolatileFoo
{
    //init_value 的最大值
    final static int MAX = 5;
    //init_value 的初始值
    static int init_value = 0;


    public static void main(String[] args)
{
        //启动一个 Reader 线程，当发现 local_value和init_value 不同时，则输出 init_value 被修改的信息
        new Thread(() ->
        {
            int localValue = init_value;
            while (localValue < MAX)
            {
                if (init_value != localValue)
                {
                    System.out.printf("The init_value is updated to [%d]\n", init_value);
                    //对 localValue 进行重新赋值
                    localValue = init_value;
                }
            }
        }, "Reader").start();


        //启动 Updater 线程，主要用于对 init_value 的修改，当 local_value>=5 的时候则退出生命周期
        new Thread(() ->
        {
            int localValue = init_value;
            while (localValue < MAX)
            {
                //修改init_value
                System.out.printf("The init_value will be changed to [%d]\n", ++localValue);
                init_value = localValue;
                try
                {
                    //短暂休眠，目的是为了使 Reader 线程能够来得及输出变化内容
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e)
                {
                    e.printStackTrace();
                }
            }
        }, "Updater").start();
    }
}

The init_value will be changed to [1]
The init_value will be changed to [2]
The init_value will be changed to [3]
The init_value will be changed to [4]
The init_value will be changed to [5]

static volatile int init_value = 0;

The init_value will be changed to [1]
The init_value is updated to [1]
The init_value will be changed to [2]
The init_value is updated to [2]
The init_value will be changed to [3]
The init_value is updated to [3]
The init_value will be changed to [4]
The init_value is updated to [4]
The init_value will be changed to [5]
The init_value is updated to [5]