例题9：
What happens when you try to compile and run the following application? Choose all correct options.
1. public class Z {
2. public static void main(String[] args) {
3. new Z();
4. }
5.
6. Z() {
7. Z alias1 = this;
8. Z alias2 = this;
9. synchronized(alias1) {
10. try {
11. alias2.wait();
12. System.out.println(“DONE WAITING”);
14. catch (InterruptedException e) {
15. System.out.println(“INTERR
UPTED”);
16. }
17. catch (Exception e) {
18. System.out.println(“OTHER EXCEPTION”);
19. }
20. finally {
21. System.out.println
(“FINALLY”);
22. }
23. }
24. System.out.println(“ALL DONE”);
25. }
26. }
A. The application compiles but doesn t print anything.
B. The application compiles and print “DONE WAITING”
C. The application compiles and print “FINALLY”
D. The application compiles and print “ALL DONE”
E. The application compiles and print “INTERRUPTED”
解答：A
点评：在Java中，每一个对象都有锁。任何时候，该锁都至多由一个线程控制。由于alias1与alias2指向同一对象Z，在执行第11行前，线程拥有对象Z的锁。在执行完第11行以后，该线程释放了对象Z的锁，进入等待池。但此后没有线程调用对象Z的notify()和notifyAll()方法，所以该进程一直处于等待状态，没有输出。
例题10：
Which statement or statements are true about the code listed below? Choose three.
1. public class MyTextArea extends TextArea {
2. public MyTextArea(int nrows, int ncols) {
3. enableEvents(AWTEvent.TEXT_
EVENT_MASK);
4. }
5.
6. public void processTextEvent
(TextEvent te) {
7. System.out.println(“Processing a text event.”);
8. }
9. }
A. The source code must appear in a file called MyTextArea.java
B. Between lines 2 and 3, a call should be made to super(nrows, ncols) so that the new component will have the correct size.
C. At line 6, the return type of processTextEvent() should be declared boolean, not void.
D. Between lines 7 and 8, the following code should appear: return true.
E. Between lines 7 and 8, the following code should appear: super.processTextEvent(te).
解答：A, B, E
点评：由于类是public，所以文件名必须与之对应，选项A正确。如果不在2、3行之间加上super(nrows,ncols)的话，则会调用无参数构建器TextArea(), 使nrows、ncols信息丢失，故选项B正确。在Java2中，所有的事件处理方法都不返回值，选项C、D错误。选项E正确，因为如果不加super.processTextEvent(te)，注册的listener将不会被唤醒。 |
