改错public class Parasitism extends Thread { public Parasitism(String name){ super(name); } public void run() { if(Thread.currentThread().isDaemon()) System.out.println(getName() + " is Daemon thread"); else System.out.println(getName() + " is User thread"); } public static void main(String[] args) { Parasitism t1 = new Parasitism("t1"); Parasitism t2 = new Parasitism("t2"); t1.start(); t2.start(); t1.setDaemon(true); }

在这个代码中，需要注意的是 `t1.setDaemon(true);` 应该在 `t1.start();` 之前调用，否则会抛出 `IllegalThreadStateException` 异常，因为在线程启动后，就不能再设置它的守护线程属性了。所以正确的代码应该是：

public class Parasitism extends Thread {
    public Parasitism(String name) {
        super(name);
    }

    public void run() {
        if (Thread.currentThread().isDaemon())
            System.out.println(getName() + " is Daemon thread");
        else
            System.out.println(getName() + " is User thread");
    }

    public static void main(String[] args) {
        Parasitism t1 = new Parasitism("t1");
        Parasitism t2 = new Parasitism("t2");
        t1.setDaemon(true);
        t1.start();
        t2.start();
    }
}