Java isAlive() 和 join()

Question

我需要一些有关 isAlive() 和 join() 函数的帮助。我了解如何以以下形式实现 isAlive() 和 join():

public class mthread implements Runnable{

public void run(){
    for (int i = 0; i <3; i++){
        System.out.println("sleep.. " + i);
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {              
            e.printStackTrace();
        }
    }       
}

public static void main(String[] args) {
    Thread a1 = new Thread (new mthread());
    Thread a2 = new Thread (new mthread());
    Thread a3 = new Thread (new mthread());
    a1.start();
    a2.start();
    a3.start();

    System.out.println("a1.isAlive() = " + a1.isAlive());
    System.out.println("a2.isAlive() = " + a2.isAlive());
    System.out.println("a3.isAlive() = " + a3.isAlive());

    try {
        a1.join();
        a2.join();
        a3.join();
    } catch (InterruptedException e) {          
        e.printStackTrace();
    }       
    System.out.println("a1.isAlive() = " + a1.isAlive());
    System.out.println("a2.isAlive() = " + a2.isAlive());
    System.out.println("a3.isAlive() = " + a3.isAlive());       
}

}

但是如果我想做这样的事情:

public class mthread implements Runnable{

public void run(){
    for (int i = 0; i <3; i++){
        System.out.println("sleep.. " + i);
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {              
            e.printStackTrace();
        }
    }       
}

public static void main(String[] args) {
    for (int i = 0; i < 20; i++){
        new Thread (new mthread()).start();
    }       

    for (int i = 0; i < 20; i++){
        **System.out.println(i + " isAlive() = " + i.isAlive());**
    }

    try {
        for (int i = 0; i < 20; i++){       
            **i.join();**           
        }
    } catch (InterruptedException e) {          
        e.printStackTrace();
    }
    for (int i = 0; i < 20; i++){
        **System.out.println(i + " isAlive() = " + i.isAlive());**
    }       
}

}

当线程没有实名时，如何实现isAlive()或join()函数？

谢谢。

Answer 1

How do I implement isAlive() or join() function when there is no real name for Thread

你不能。 ; )当您不为变量分配某些内容时，您将永远失去对它的跟踪。 (从技术上讲，Thread 在这方面是一个 little 位 special。)

您可以将您的线程放在 array 中跟踪它们。

Thread[] threads = new Thread[20];

for (int i = 0; i < threads.length; i++) {
    threads[i] = new Thread(new mthread());
    threads[i].start();
}       

for (int i = 0; i < threads.length; i++) {
    System.out.println(i + " isAlive() = " + threads[i].isAlive());
}

try {
    for (int i = 0; i < threads.length; i++){       
        threads[i].join();           
    }
} catch (InterruptedException e) {          
    e.printStackTrace();
}
for (int i = 0; i < threads.length; i++) {
    System.out.println(i + " isAlive() = " + threads[i].isAlive());
}

作为旁注，Java 中的类名称按照惯例以大写字母开头。您的mthread应该是MThread。它也可能应该是 MRunnable，因为它是 Runnable，而不是 Thread。