Question

我有以下课程

class ThreadDemo extends Thread {
    private Thread t;
    private String threadName;

    ThreadDemo( String name) {
        threadName = name;
    }

    public void run() {
        for(int i = 5; i > 0; i--) {
            System.out.println("Thread " +  threadName + " Counter   ---   "  + i );
        }

        try {
            Thread.sleep(1000);
        } catch (Exception e) {
            System.out.println("Sleep issue");
        }

        System.out.println("Finishing run");

        try {
            Thread.sleep(1000);
        } catch (Exception e) {
            System.out.println("Sleep issue");
        }
    }

    public void start () {
        t = new Thread (this, threadName);
        t.start ();
    }
}

如下所示进行测试

public class Main {
    public static void main(String[] args) {
        ThreadDemo T1 = new ThreadDemo( "Thread - 1 ");
        ThreadDemo T2 = new ThreadDemo( "Thread - 2 ");
        T1.start();
        T2.start();

        //Let's give some time for threads to run
        try {
            Thread.sleep(10);
        } catch (Exception e) {
            System.out.println("Main sleep issue");
        }

        try {
            T1.join();
            T2.join();
        } catch ( Exception e) {
            System.out.println("Interrupted");
        }

        System.out.println("Finishing main.");
    }
}

为什么我总是得到＆＃34;完成主要＆＃34;之前＆＃34;完成运行＆＃34;尽管我使用T1.join（）和T2.join（）来等待它们完成，但在输出中？最初我认为这可能是由于缓冲延迟所以我在run（）的末尾添加了Thread.sleep（1000）以给出一些时间来打印＆＃34;完成运行＆＃34;但它没有帮助。我猜它是由于第一次出现Thread.sleep（1000）（当我删除它时，它工作正常）但不知道为什么。

Answer 1

因为这个原因：

public void start () {
    t = new Thread (this, threadName);
    t.start ();
}

因此，您的ThreadDemo实例永远不会作为线程启动：打印Finishing run消息的线程是在该方法中创建的线程。该线程与ThreadDemo之间没有链接。

删除start()方法。

java Thread.join没有按预期工作

1 个答案: