多选题 Given:
2. public class Bang extends Thread {
3. static Thread t1, t2, t3;
4. public static void main(String[] args) throws Exception {
5. t1 = new Thread(new Bang());
6. t2 = new Thread(new Bang());
7. t3 = new Thread(new Bang());
8. t1.start(); t2.start(); t3.start();
9. }
10. public void run() {
11. for(int i = 0; i ＜ 500; i++) {
12. System.out.print(Thread.currentThread() .getId() + " ");
13. if(i == 250)
14. try {
15. System.out.print ("**" + tl.getId() + "**");
16. t1.sleep(600);
17. }
18. catch (Exception e) { }
19. } } }
Which are true? (Choose all that apply.)