java多线程卖票问题，解决线程安全

需求：设计程序，利用多线程的思想模拟三个售票员卖50张票的功能

package com.demo.first;
public class Demo03 {

	public static void main(String[] args) {
		Object obj = new Object();
		WindowThread thread01 = new WindowThread("窗口一", obj);
		WindowThread thread02 = new WindowThread("窗口二", obj);
		WindowThread thread03 = new WindowThread("窗口三", obj);
		//开启线程
		thread01.start();
		thread02.start();
		thread03.start();
	}
}
class WindowThread extends Thread {
	public static int ticket = 50;
	//设置线程共有对象，方便加锁
	Object obj;
	public WindowThread(String name, Object obj) {
		super(name);
		this.obj = obj;
	}
	@Override
	public void run() {
		while (true) {
		//加锁。确保线程安全，不发生一个资源多次被使用
			synchronized (obj) {
				if (ticket > 0) {
					String message = Thread.currentThread().getName() + "卖了第" + ticket + "票";
					System.out.println(message);
					ticket--;
				} else {
					break;
				}

			}
		}

	}
}