一个小小的问题，求大神帮忙解释一下 - 黑马程序员技术交流社区

class Resource{
private String name;
private int count = 1;
private boolean flag = false;
public synchronized void set(String name) {
while(flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
this.name = name+"..."+count++;
System.out.println(Thread.currentThread().getName()+"...生产者.."+this.name);
flag = true;
this.notifyAll();
}
public synchronized void out(){
while(!flag){ //当处于等待状态的线程被唤醒时，应该再进行一次标志的判断，故而将if更换为while
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread().getName()+".....消费者...."+this.name);
flag = false;
this.notifyAll(); //因为在等待的线程池中，先进入线程池中的会先唤醒，所以需要用notifyAll唤醒所有的线程
}
}
class Producer implements Runnable{
private Resource res;
public Producer(Resource res) {
this.res = res;
}
public void run() {
while(true){
res.set("+商品+");
}
}
}
class Consumer implements Runnable{
private Resource res;
public Consumer(Resource res) {
this.res = res;
}
public void run() {
while(true){
res.out();
}
}
}
public class ProducerConsumerDemo {
public static void main(String[] args) {
Resource r = new Resource();
/*
* 当开启的线程超过两个时，这段代码会出现问题
*
*/
//new Thread(new Producer(r)).start(); //代码优化的写法
Producer pro = new Producer(r);
Consumer con = new Consumer(r);
Thread t1 = new Thread(pro);
Thread t2 = new Thread(pro);
Thread t3 = new Thread(con);
Thread t4 = new Thread(con);
t1.start();
t2.start();
t3.start();
t4.start();
}
}

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