Java多线程之可见性与原子性——synchronized VS volatile

<转：http://blog.csdn.net/uniquewonderq/article/details/48113071>



































程序举例：

代码：

[java] view plain copy

package com.synch;

public class SynchronizedDemo {

//共享变量

private boolean ready = false;

private int result = 0;

private int number = 1;

//写操作

public synchronized void write(){

ready = true;

number = 2;

}

//读操作

public synchronized void read(){

if(ready){

result = number*3;

}

System.out.println("result的值为：" + result);

}

//内部线程类

private class ReadWriteThread extends Thread {

//根据构造方法中传入的flag参数，确定线程执行读操作还是写操作

private boolean flag;

public ReadWriteThread(boolean flag){

this.flag = flag;

}

@Override

public void run() {

if(flag){

//构造方法中传入true，执行写操作

write();

}else{

//构造方法中传入false，执行读操作

read();

}

}

}

public static void main(String[] args) {

SynchronizedDemo synDemo = new SynchronizedDemo();

//启动线程执行写操作

synDemo .new ReadWriteThread(true).start();

// try {

// Thread.sleep(1000);

// } catch (InterruptedException e) {

// // TODO Auto-generated catch block

// e.printStackTrace();

// }

//启动线程执行读操作

synDemo.new ReadWriteThread(false).start();

}

}

















代码示例：

[java] view plain copy

package com.synch;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

public class VolatileDemo {

private Lock lock = new ReentrantLock();

private int number = 0;

public int getNumber(){

return this.number;

}

public void increase(){

try {

Thread.sleep(100);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

lock.lock();

try {

this.number++;

} finally {

lock.unlock();

}

}

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

final VolatileDemo volDemo = new VolatileDemo();

for(int i = 0 ; i < 500 ; i++){

new Thread(new Runnable() {

@Override

public void run() {

volDemo.increase();

}

}).start();

}

//如果还有子线程在运行，主线程就让出CPU资源，

//直到所有的子线程都运行完了，主线程再继续往下执行

while(Thread.activeCount() > 1){//让所有的子线程都执行完后，然后再执行<pre name="code" class="java">//System.out.println("number : " + volDemo.getNumber()); 语句。因为主线程算一个。当活跃线程为1时，也就是所有的子线程执行完毕了。此///时退出while 循环执行输出语句。

Thread.yield();}System.out.println("number : " + volDemo.getNumber());}}