比老师更好的例子（两个不同线程的互斥与同步）

这是一个生产者与消费者的例子（更简单易懂）
窝头类（商品）

class WoTou { 
    int id; 
    public WoTou(int id) { 
        this.id = id; 
    } 
    public String toString() { 
        return "WoTou "+id; 
    } 
} 

生产者与消费者（锁操作）

class SyncStack { 
    int index = 0; 
    WoTou[] arrwt = new WoTou[6]; 
    public synchronized void push(WoTou wt) {
        //生产者 
        while(index==arrwt.length-1) { 
            try { 
                this.wait(); 
            }catch(InterruptedException e) { 
                e.printStackTrace(); 
                } 
        } 
        this.notify(); 
        arrwt[index] = wt; 
        index ++; } 
    public synchronized WoTou pop() {
        //消费者
        while(index==0) { 
            try { 
                this.wait(); 
            }catch(InterruptedException e) { 
                e.printStackTrace(); 
            } 
        } 
        this.notify(); 
        index--; 
        return arrwt[index];
    } 
} 

生产线程

class Producer implements Runnable { 
    SyncStack ss = null; 
    public Producer(SyncStack ss) { 
        this.ss = ss; 
    } 
    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()*50));
            }catch(InterruptedException e) {
                e.printStackTrace(); 
            } 
        } 
    } 
} 

消费线程

class Consumer implements Runnable{ 
    SyncStack ss = null;
    public Consumer(SyncStack ss) {
        this.ss = ss; 
    } 
    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();
            } 
        } 
    } 
}

测试

public class ConsumerProducer { 
    public static void main(String[] args) { 
        SyncStack ss = new SyncStack(); 
        Producer p = new Producer(ss); 
        Consumer c = new Consumer(ss); 
        new Thread(p).start(); new Thread(c).start(); 
    } 
}