线程同步生产者消费者问题

public class ProducerConsumer{
    public static void main(String[] args){
        WtStack st = new WtStack();
        Producer a = new Producer(st);
        Consumer b = new Consumer(st);
        new Thread(a).start();
        new Thread(b).start();
    }
}

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

class WtStack {
    int index=0;
    WoTou[] wtarr = new WoTou[10];
    
    public synchronized void push(WoTou wt){
        while(index==wtarr.length){
            try{
                this.wait();
            }catch(InterruptedException e){
                e.printStackTrace();
            }
        }
        this.notify();
        wtarr[index]= wt;
        index++;    
    }
    
    public synchronized WoTou pop(){
        while(index==0){
            try{
                this.wait();
            }catch(InterruptedException e){
                e.printStackTrace();
            }
        }
        this.notify();
        index--;
        return wtarr[index];
    }
}

class Producer implements Runnable {
    WtStack st = null;
    Producer(WtStack a){
        this.st = a;
    }
    public void run(){
        for(int i=0;i<20;i++){
            WoTou wt = new WoTou(i);
            st.push(wt);
            System.out.println("生产了："+wt);
        }
        try{
            Thread.sleep(1000);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
    }
}

class Consumer implements Runnable {
    WtStack st = null;
    Consumer(WtStack a){
        this.st = a; 
    }
    public void run(){
        for(int i=0;i<20;i++){
            System.out.println(st.pop());
        }
        try{
            Thread.sleep(1000);
        }catch(InterruptedException e){
            e.printStackTrace();
        }
    }
}