java - Notify() 不能与 Wait() 一起使用

Question

我是线程和学习新手，但在下面的代码中为什么通知不起作用。根据我的理解，当 i=5 时，notify 应该执行主线程并打印总数。如有错误请指正。

public class ThreadA {
public static void main(String[] args){
    ThreadB b = new ThreadB();
    b.start();

    synchronized(b){
        try{
            System.out.println("Waiting for b to complete...");
            b.wait();
        }catch(InterruptedException e){
            e.printStackTrace();
        }

        System.out.println("Total is: " + b.total);
    }
}
}

class ThreadB extends Thread{
    int total;
    @Override
    public void run(){
        synchronized(this){
            for(int i=0; i<10 ; i++){
                total += i;
             if(i==5){ 
                 System.out.println("Notify");
                 notify();
                 }
                System.out.println("Total is in cal thread: "+i+":" + total);
            }

        }
    }
}

这是程序的输出:

Waiting for b to complete... 
Total is in cal thread: 0:0 
Total is in cal thread: 1:1 
Total is in cal thread: 2:3 
Total is in cal thread: 3:6 
Total is in cal thread: 4:10 
Notify 
Total is in cal thread: 5:15 
Total is in cal thread: 6:21 
Total is in cal thread: 7:28 
Total is in cal thread: 8:36 
Total is in cal thread: 9:45 
Total is: 45 – 

Answer 1

synchronized(b){
    try{
        System.out.println("Waiting for b to complete...");
        b.wait();

调用notify仅影响当前等待的线程，调用后开始等待的线程不会受到影响。在您可以在同步块(synchronized block)内 100% 确认您正在等待的事情尚未发生之前，请勿调用 wait。