通过扩展Thread类来创建线程

Question

这是一个有关通过扩展Thread类创建线程的简单示例。

class Count extends Thread {

    Count() {
        super("my extending thread");
        System.out.println("my new thread is started " + this);
        start();
    }

    @Override
    public void run() {
        try {
            for (int i = 0; i < 10; i++) {
                System.out.println("count " + i);
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("my thread run is over");
        }
    }

}

public class Multi2 {

    public static void main(String[] args) {
        Count c = new Count();
        try {
            while (c.isAlive()) {
                System.out.println("main thread is alive untill child thread is alive");
                Thread.sleep(1500);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("main thread is over");
        }
    }
}

我的输出就是这个。

my new thread is started Thread[my extending thread,5,main]
main thread is alive untill child thread is alive
count 0
count 1
main thread is alive untill child thread is alive
count 2
main thread is alive untill child thread is alive
count 3
count 4
main thread is alive untill child thread is alive
count 5
main thread is alive untill child thread is alive
count 6
count 7
main thread is alive untill child thread is alive
count 8
main thread is alive untill child thread is alive
count 9
my thread run is over
main thread is over

我的问题是

01. main thread is alive untill child thread is alive如何main thread is alive untill child thread is alive之前输出
count 0 count 1

02.在main thread is alive untill child thread is alive输出之前， main thread is alive untill child thread is alive保持main thread is alive untill child thread is alive并与run()方法的输出一起继续打印？

请帮我解决这个问题。
谢谢。

Answer 1

Count有这一行：

Thread.sleep(1000);

您的主程序有这一行：

Thread.sleep(1500);

显然，您将获得每3个计数打印2个主要打印。 这就是0和1彼此相邻的原因。

至于为什么要在计数打印之前看到主打印，您可以看到以下内容：

Count c = new Count();
try {
while (c.isAlive()) {
    System.out.println("main thread is alive untill child thread is alive");
    Thread.sleep(1500);

您已经关闭了c但是直到JVM执行上下文切换以实际运行该线程之前，您可能看不到结果。 事实是，在某些系统上，您可能会在此之前查看计数器。 通常，因为它离开始时还很近并且还没有屈服，所以您会在柜台前看到主要印刷品。

对于第二部分，您的main thread is...继续打印，因为它有一个循环，告诉您要进行打印直到计数器线程不再存在为止。 它们都使用System.out因此当您查看控制台时，都可以在其中看到它们。