本文共 2313 字，大约阅读时间需要 7 分钟。

先看代码：

import java.util.concurrent.atomic.AtomicInteger;/** * * @author xialuomantian */public class NewTest {    static volatile int a = 1;    static volatile int b = 1;    //static  int a = 1;    //static  int b = 1;    public static AtomicInteger aa = new AtomicInteger(0);    public static AtomicInteger bb = new AtomicInteger(0);    public static AtomicInteger ab = new AtomicInteger(0);        static void add() {        a++;        b++;    }    static synchronized void print() {        if (a > b) {            aa.getAndIncrement();                   } else if (a < b) {            bb.getAndIncrement();        } if (a == b) {            ab.getAndIncrement();        }    }    public static void main(String[] args) {        System.out.println(Thread.currentThread().getName());        for (int i = 0; i < 100000; i++) {            new Thread(() -> {                               add();                print();            }).start();        }        System.out.println("a>b:" + aa);        System.out.println("b>a:" + bb);        System.out.println("a==b:" + ab);    }}

再去掉volatile

/* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and open the template in the editor. */package com.mycompany.mytest;import java.util.concurrent.atomic.AtomicInteger;/** * * @author xialuomantian */public class NewTest {    static  int a = 1;    static  int b = 1;    public static AtomicInteger aa = new AtomicInteger(0);    public static AtomicInteger bb = new AtomicInteger(0);    public static AtomicInteger ab = new AtomicInteger(0);        static void add() {        a++;        b++;    }    static synchronized void print() {        if (a > b) {            aa.getAndIncrement();                   } else if (a < b) {            bb.getAndIncrement();        } if (a == b) {            ab.getAndIncrement();        }    }    public static void main(String[] args) {        System.out.println(Thread.currentThread().getName());        for (int i = 0; i < 100000; i++) {            new Thread(() -> {                               add();                print();            }).start();        }        System.out.println("a>b:" + aa);        System.out.println("b>a:" + bb);        System.out.println("a==b:" + ab);    }}

下面是几种结果：

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