java的int类型线程安全

本文转载自：http://blog.csdn.net/xiaoyezi1001/article/details/25504935

一、测试int为线程不安全

在Java中，高并发/多线程情况下，int的自增自减操作都不是线程安全的，使用AtomicInteger可以保证。

 package com.yezi.learn.atomic;
 import java.util.concurrent.atomic.AtomicInteger;
 /**
  * Created by yezi on 2014/5/10.
  */
 public class TestAtomicInteger {
     private int shareI=0;
     private AtomicInteger atomicLoop = new AtomicInteger(0);
     private int loop =0;
     public static void main(String []args) throws Exception{
         TestAtomicInteger t = new TestAtomicInteger();
         t.testMethod();
         System.out.println(t);
     }
     public void testMethod() throws Exception{
         Thread th1 = new Thread(new ThreadTest());
         Thread th2 = new Thread(new ThreadTest());
         th1.start();
         th2.start();
         th1.join();
         th2.join();
     }
     public synchronized void add(){
         shareI++;
     }
     class ThreadTest implements Runnable{
         @Override
         public void run() {
             //testAtomicInteger();
             testInt();
         }
     }
     public void testInt(){ //测试，输出结果随机，为线程不安全
         for(;loop<100000;loop++) {
             add();
         }
     }
     public void testAtomicInteger(){  //输出1000000，线程安全
         for(;atomicLoop.getAndAdd(1)<100000;) {
             add();
         }
     }
     @Override
     public String toString() {
         return ""+shareI;
     }
 }

二、AtomicIntegerFieldUpdater可以对Obj的字段进行处理

 package com.yezi.learn.atomic;
 import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 /**
  * Created by yezi on 2014/5/10.
  */
 public class TestAtomicObjectInteger {
     private Looper looper = new Looper();
     private int shareI=0;
     public static void main(String ...args) throws Exception{
         TestAtomicObjectInteger t = new TestAtomicObjectInteger();
         t.testMethod();
         System.out.println(t);
     }
     public void testNormal(){ //线程不安全的
         for(;looper.getLoop()<100000;looper.setLoop(looper.getLoop()+1)){
             add();
         }
     }
     public void testUseAtomic(){
         AtomicIntegerFieldUpdater atomicIntegerFieldUpdater =  //使用Atomic来进行自加
                 AtomicIntegerFieldUpdater.newUpdater(Looper.class,"loop");
         for(;atomicIntegerFieldUpdater.getAndAdd(looper,1)<100000;){
             add();
         }
     }
     public void testMethod() throws Exception{
         Thread th1 = new Thread(new ThreadTest());
         Thread th2 = new Thread(new ThreadTest());
         th1.start();
         th2.start();
         th1.join();
         th2.join();
     }
     class ThreadTest implements Runnable{
         @Override
         public void run() {
             testUseAtomic();
             //testNormal();
         }
     }
     public synchronized void add(){
         shareI++;
     }
     @Override
     public String toString() {
         return shareI+"";
     }
 }
 class Looper{
     public volatile int loop=0;  //对于AtomicIntegerFieldUpdater要控制的字段必须为public volatile
     public int getLoop() {
         return loop;
     }
     public void setLoop(int loop) {
         this.loop = loop;
     }
 }