5-19

本题要求主线程退出时，在main方法中所启动的线程t1也要自动结束。

public class Main {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(new PrintTask());
        

t1.setDaemon(true);

t1.join();

System.out.println(Thread.currentThread().getName() + " end"); } }

5-21

本题目要求t1线程打印完后，才执行主线程main方法的最后一句System.out.println(Thread.currentThread().getName()+" end");

public class Main {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(new PrintTask());
        

t1.start();

t1.join();

System.out.println(Thread.currentThread().getName()+" end"); } }