java - 了解Java中多线程的概念

Question

最近我完成了一个简单的线程程序，这给我带来了一些相关概念的问题......我的示例程序代码如下所示:

class NewThread implements Runnable {
    Thread t;
    NewThread() {
        t = new Thread(this, "Demo Thread");
        System.out.println("Child thread: " + t);
        t.start(); // Start the thread
    }
    public void run() {
        try {
            for (int i = 5; i > 0; i--) {
                System.out.println("Child Thread: " + i);
                Thread.sleep(500);
            }
        } catch (InterruptedException e) {
            System.out.println("Child interrupted.");
        }
        System.out.println("Exiting child thread.");
    }
}
class ThreadDemo {
    public static void main(String args[]) {
        new NewThread(); // create a new thread
        try {
            for (int i = 5; i > 0; i--) {
                System.out.println("Main Thread: " + i);
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            System.out.println("Main thread interrupted.");
        }
        System.out.println("Main thread exiting.");
    }
}

现在这个程序给我的输出如下:

Child thread: Thread[Demo Thread,5,main]
Main Thread: 5
Child Thread: 5
Child Thread: 4
Main Thread: 4
Child Thread: 3
Child Thread: 2
Main Thread: 3
Child Thread: 1
Exiting child thread.
Main Thread: 2
Main Thread: 1
Main thread exiting.

所以，这对我来说非常清楚。但是，一旦我将对象创建代码(调用 NewThread 类构造函数)替换为如下所示:

NewThread nt = new NewThread(); // create a new thread

输出变得有点不同，如下所示:

Child thread: Thread[Demo Thread,5,main]
Main Thread: 5
Child Thread: 5
Child Thread: 4
Child Thread: 3
Main Thread: 4
Child Thread: 2
Child Thread: 1
Main Thread: 3
Exiting child thread.
Main Thread: 2
Main Thread: 1
Main thread exiting.

有时，这两种情况都会给我相同的输出。因此，我在这两种情况下都没有得到确切的变化。

我想知道输出的变化是在这里吗？

提前致谢...

Answer 1

改变的输出是由于操作系统进程调度和 JVM 线程调度的性质造成的。即使您取出第二个线程，也不能保证您的线程会在 500 毫秒后准确唤醒。