SCJP題庫第221題

Given:

7. void waitForSignal(){

8.   Object obj = new Object();

9.   synchronized(Thread.currentThread()){

10.   obj.wait();

11.   obj.notify();

12.  }

13.}

Which statement is true?

 

A. This code can throw an InterruptedException.

B. This code can throw an IllegalMonitorStateException.

C. This code can throw a TimeoutException after ten minutes.

D. Reversing the order of obj.wait() and obj.notify() might cause this method to complete normally.

E. A call to notify() or notifyAll() from another thread might cause this method to complete normally.

F. This code does NOT compile unless "obj.wait()" is replaced with "((Thread) obj).wait()".

Ans: B

解說: IllegalMonitorStateException是說一個執行緒試圖在未取得物件lock時，去對該物件進行等待(wait)或通知(notify)的動作，會產生的一個不合法的監控狀態例外。


正確的程式寫法應如下：
 synchronized(obj) {
}


取行obj的lock後，方能對obj進行wait或notify。