java - Java中使用监视器类同步线程

Question

以下程序创建生成随机数的线程。

我如何更改Monitor类，以便它能够以按每个线程ID的顺序打印输出的方式控制线程？

不接受“调用 run 方法而不是 start”之类的解决方案。

给定的类别是:

public class Main {
    public static void main(String[] args) {
        Monitor mon = new Monitor();
        for (int i = 0; i < 20; i++)
            new T(i, mon).start();

        System.out.println("Finished");
    }
}

<小时/>

public class Monitor {

    public void print(int id, int num) {
        System.out.println("id=" + id + " num=" + num);
    }
}

<小时/>

public class T extends Thread {
    private int id;
    private Monitor mon;

    public T(int i, Monitor m) {
        id = i;
        mon = m;
    }

    private int calc() {
        int num = 0;
        for (int i = 0; i < 10; i++)
            num = num + (int) (Math.random() * 10);
        return num;
    }

    public void run() {
        int num = calc();
        mon.print(id, num);
    }
}

Answer 1

您只需要尝试打印的线程等待并阻塞，直到其 ID 达到预期的 ID:

public class Monitor {

    private final Object lock = new Object();
    private int expectedId = 0;

    public void print(int id, int num) {
        synchronized (lock) {
            while (id != expectedId) {
                try {
                    lock.wait();
                }
                catch (InterruptedException e) {
                    return;
                }
            }
            System.out.println("id=" + id + " num=" + num);
            expectedId++;
            lock.notifyAll();
        }
    }
}