问为什么守护进程线程在非守护进程线程完成后执行？

EN

class DaemonDemo implements Runnable {

    Thread th;

    DaemonDemo() {
        th = new Thread(this);

        th.setDaemon(true);
        th.start();
    }

    public void run() {
        System.out.println("Run: " + th.isDaemon());

        for (int i = 1; i <= 10; i++) {
            System.out.println("Run: " + i);
        }
    }
}

public class Test_DaemonDemo {

    public static void main(String[] args) {

        DaemonDemo dd = new DaemonDemo();

        System.out.println("Main Countdown Starts");

        for (int i = 1; i <= 10; i++) {
            System.out.println("main: " + i);
        }
    }
}

Main Countdown Starts
Run: true
main: 1
Run: 1
main: 2
Run: 2
main: 3
Run: 3
main: 4
Run: 4
main: 5
Run: 5
main: 6
Run: 6
main: 7
Run: 7
main: 8
main: 9
main: 10
Run: 8
Run: 9
Run: 10