多选题 Given:
2. public class Checkout2 implements Runnable {
3. void doStuff() { }
4. synchronized void doSynch() {
5. try {Thread.sleep(1000); }
6. catch (Exception e) {System.out.print("e "); }
7. }
8. public static void main(String[] args) {
9. long start = System.currentTimeMillis();
10. new Thread(new Checkout2()) .start();
11. Thread t1 = new Thread(new Checkout2());
12. t1.start();
13. try {t1.join();}
14. catch (Exception e) {System.out.print("e "); }
15. System.out.print in ("elapsed: " + (System.currentTimeMillis() - start));
16. }
17. public void run() {
18. for(int j = 0; j ＜ 4; j++) {
19. doStuff();
20. try {Thread.sleep(1000); }
21. catch (Exception e) {System.out.print("e "); }
22. doSynch();
23. } } }
Which are true? (Choose all that apply.)

A、 Compilation fails.
B、 Elapsed time will be about eight seconds.
C、 Elapsed time will be about nine seconds.
D、 Elapsed time will be about 12 seconds.
E、 Changing doSynch() to be unsynchronized will change elapsed by only a few milliseconds.
F、 Changing doSynch() to be unsynchronized will change elapsed by 450 or more milliseconds.

【正确答案】 B、E

【答案解析】