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

程序举例：

代码：

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：

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());}}

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