SCJP 1.6版考題 221

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()".

解答

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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。