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：
