檢視 SCJP 1.6版考題 235 的原始碼

<br>Given:
<br>11. &nbsp; public class PingPong implements Runnable{ 
<br>12. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;synchronized void hit(long n){ 
<br>13. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for(int i=1; i&lt;3; i++) 
<br>14. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(n + "-" + i + " "); 
<br>15. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} 
<br>16. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public static void main(String[] args){ 
<br>17. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;new Thread(new PingPong()).start(); 
<br>18. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;new Thread(new PingPong()).start(); 
<br>19. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } 
<br>20. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;public void run(){ 
<br>21. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;hit(Thread.currentThread().getId); 
<br>22. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } 
<br>23. &nbsp; }

<br>Which two statements are true? (Choose two.) 
<br>&nbsp;A. The output could be 8-1 7-2 8-2 7-1 
<br>&nbsp;B. The output could be 7-1 7-2 8-1 6-1 
<br>&nbsp;C. The output could be 8-1 7-1 7-2 8-2 
<br>&nbsp;D. The output could be 8-1 8-2 7-1 7-2 




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<span style="font-size:medium;">解答</span>

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<span style="font-size: medium;">Ans: CD   </span>

<span style="font-size:medium;"> 解說:
run方法會去呼叫同步方法hit，二條執行緒各自有獨立的hit方法執行，i必然是依1與2的順序輸出，
<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;A答案中執行緒7先跑2再跑1是錯的，答案B出現一條執行緒6，程式只建二條執行緒不可能出現第3條執行緒。 


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