多线程下生产者与消费者的问题

package com.yql.thread;

//生产者与消费者问题java代码实现
public class ProducerConsumer {
	public static void main(String[] args) {
		//创建一个栈用来放窝头
		SyncStack ss = new SyncStack();
		//生产者p
		Producer p = new Producer(ss);
		//消费者c
		Consumer c = new Consumer(ss);
		//开启生产者消费者线程各两个，模拟两个买窝头两个生产窝头
		new Thread(p).start();
		new Thread(p).start();
		new Thread(p).start();
		new Thread(c).start();
	}
}
//窝头类
class WoTou {
	int id; 
	WoTou(int id) {
		this.id = id;
	}
	public String toString() {
		return "WoTou : " + id;
	}
}
//用来装窝头的栈
class SyncStack {
	int index = 0;
	//最多容纳6个窝头
	WoTou[] arrWT = new WoTou[6];
	//同步出栈的方法
	public synchronized void push(WoTou wt) {
		//只要窝头满栈了就让该线程wait等待其他方法唤醒
		while(index == arrWT.length) {
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		//唤醒其他等待该同步锁的所有线程
		this.notifyAll();		
		arrWT[index] = wt;
		index ++;
	}
	//同步进栈的方法
	public synchronized WoTou pop() {
		//一旦窝头栈空了就让该线程wait等待其他方法唤醒
		while(index == 0) {
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		//唤醒其他等待该同步锁的所有对象
		this.notifyAll();
		index--;
		return arrWT[index];
	}
}
//生产者 实现了runnable接口 可以用于多线程
class Producer implements Runnable {
	SyncStack ss = null;
	Producer(SyncStack ss) {
		this.ss = ss;
	}
	//模拟生产20个窝头，每生产一个就将其放入到窝头栈中
	public void run() {
		for(int i=0; i<20; i++) {
			WoTou wt = new WoTou(i);
			ss.push(wt);
            System.out.println("生产了：" + wt);
			try {
				Thread.sleep((int)(Math.random() * 200));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}			
		}
	}
}
//消费者
class Consumer implements Runnable {
	SyncStack ss = null;
	Consumer(SyncStack ss) {
		this.ss = ss;
	}
	//模拟消费20个窝头
	public void run() {
		for(int i=0; i<20; i++) {
			WoTou wt = ss.pop();
            System.out.println("消费了: " + wt);
			try {
				Thread.sleep((int)(Math.random() * 1000));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}			
		}
	}
}