java 线程同步-卖票有关问题

java 线程同步--卖票问题

线程同步方法：

（1）、同步代码块，格式：

synchronized （同步对象）{

//同步代码

}

（2）、同步方法，格式：

在方法前加synchronized修饰

问题:

多个人同时买票。

1、资源没有同步。

package thread;

public class Tickets implements Runnable {

	private int count = 5;

	@Override
	public void run() {
		for (int i = 0; i < 10; ++i) {
			if (count > 0) {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				System.out.println(count--);
			}
		}
	}
	
	public static void main(String[] args) {
		Tickets tickets=new Tickets();
        Thread t1=new Thread(tickets);
        Thread t2=new Thread(tickets);
        Thread t3=new Thread(tickets);
        t1.start();
        t2.start();
        t3.start();
    }

}

运行结果：

5
3
4
2
2
1

很明显结果是错的。

2、同步代码块

run方法中进行同步，也就是对共享资源（票数、count）进行同步

package thread;

public class Tickets implements Runnable {

	private int count = 5;

	@Override
	public void run() {
		for (int i = 0; i < 10; ++i) {
			synchronized (this) {
				if (count > 0) {
					try {
						Thread.sleep(1000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println(count--);
				}
			}
		}
	}

	public static void main(String[] args) {
		Tickets tickets = new Tickets();
		Thread t1 = new Thread(tickets);
		Thread t2 = new Thread(tickets);
		Thread t3 = new Thread(tickets);
		t1.start();
		t2.start();
		t3.start();
	}

}

3、同步方法

package thread;

public class Tickets implements Runnable {

	private int count = 5;

	@Override
	public void run() {
		for (int i = 0; i < 10; ++i) {
			sale();
		}
	}

	public synchronized void sale() {
		if (count > 0) {
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(count--);
		}
	}

	public static void main(String[] args) {
		Tickets tickets = new Tickets();
		Thread t1 = new Thread(tickets);
		Thread t2 = new Thread(tickets);
		Thread t3 = new Thread(tickets);
		t1.start();
		t2.start();
		t3.start();
	}

}

参考：http://www.cnblogs.com/rollenholt/archive/2011/08/28/2156357.html 。特此声明。