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SCJP 1.6版考題 236 - 修訂歷史
2026-05-04T12:49:02Z
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Ikk：新頁面: Given: <br>1. class Computation extends Thread{ <br>2. <br>3. private int num; <br>4. pri...
2013-03-27T13:34:37Z
<p>新頁面: Given: <br>1. class Computation extends Thread{ <br>2. <br>3. private int num; <br>4. pri...</p>
<p><b>新頁面</b></p><div>Given: <br />
<br>1. &nbsp; class Computation extends Thread{ <br />
<br>2. <br />
<br>3. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; private int num; <br />
<br>4. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; private boolean isComplete; <br />
<br>5. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; private int result; <br />
<br>6. <br />
<br>7. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public Computation(int num){this.num = num;} <br />
<br>8. <br />
<br>9. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public synchronized void run(){ <br />
<br>10. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; result = num * 2; <br />
<br>11. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; isComplete = true; <br />
<br>12. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; notify();<br />
<br>13. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} <br />
<br>14. <br />
<br>15. &nbsp;public synchronized int getResult(){<br />
<br>16. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;while(!isComplete){ <br />
<br>17. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; try{ <br />
<br>18. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;wait(); <br />
<br>19. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}catch(InterruptedException e){} <br />
<br>20. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}<br />
<br>21. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;return result; <br>22. &nbsp; } <br />
<br>23.<br />
<br>24. &nbsp; public static void main(String[] args){ <br />
<br>25. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Computation[] computations = new Computation[4]; <br />
<br>26. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for(int i=0; i&lt;computations.length; i++){ <br />
<br>27. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;computations[i] = new Computation(i); <br />
<br>28. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;computations[i].start(); <br />
<br>29. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} <br />
<br>30. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for(Computation c&nbsp;: computations) <br />
<br>31. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(c.getResult() + " "); <br />
<br>32. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} <br />
<br>33. &nbsp; } <br />
<br> <br />
<br><br />
<br>What is the result? <br> <br />
<br>A. The code will deadlock. <br />
<br>B. The code may run with no output. <br />
<br>C. An exception is thrown at runtime. <br />
<br>D. The code may run with output "0 6".<br />
<br>E. The code may run with output "2 0 6 4".<br />
<br>F. The code may run with output "0 2 4 6". <br />
<br />
<br />
<br />
<br />
<br />
<div class="toccolours mw-collapsible mw-collapsed"><br />
<span style="font-size:medium;">解答</span><br />
<br />
----<br />
<div class="mw-collapsible-content"><br />
<span style="font-size: medium;">Ans: F </span><br />
<br />
<span style="font-size:medium;"> 解說:<br />
第25~29行建立四個Thread物件，然後分別啟動這四個執行緒物件… <br />
<br> <br>緊接著30~31行分別讓四個執行緒物件呼叫getResult方法，然後分別進入對各自執行緒物件的等待事件中… <br />
<br>最後四個執行緒的run方法分別通知各自執行緒離開wait狀態…<br />
<br> <br />
<br>比較可能的輸出是F，因為各執行緒物件的num是依for迴圈0~3再乘以2得來，輸出依0 2 4 6的機率較高。<br />
</span> <br />
</div></div><br />
{{SCJP 1.6版考題講解}}</div>
Ikk