檢視 SCJP 1.6版考題 233 的原始碼

<br>Given: 
<br>1. &nbsp;public class Threads1{ 
<br>2. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int x = 0; 
<br>3. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public class Runner implements Runnable{ 
<br>4. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public void run(){ 
<br>S. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int current = 0; 
<br>6. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;for(int i=0; i&lt;4; i++){ 
<br>7. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;current = x; 
<br>8. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;System.out.print(current + ", "); 
<br>9. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; x = current + 2; 
<br>10. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } 
<br>11. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} 
<br>12. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} <br>13. <br>14. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public static void main(String[] args){ 
<br>15. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;new Threads1().go(); 
<br>16. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;} 
<br>17. 
<br>18. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;public void go(){ 
<br>19. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Runnable rl = new Runner(); 
<br>20. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;new Thread(r1).start(); 
<br>21. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;new Thread(r1).start(); 
<br>22. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } <br>23. &nbsp;}



<br>Which two are possible results? (Choose two.) <br> 
<br>A. 0, 2, 4, 4, 6, 8, 10, 6, 
<br>B. 0, 2, 4, 6, 8, 10, 2, 4, 
<br>C. 0, 2, 4, 6, 8, 10, 12, 14, 
<br>D. 0, 0, 2, 2, 4, 4, 6, 6, 8, 8, 10, 10, 12, 12, 14, 14, 
<br>E. 0, 2, 4, 6, 8, 10, 12, 14, 0, 2, 4, 6, 8, 10, 12, 14, 

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

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

<span style="font-size:medium;"> 解說:
第20與21行各新增一條執行緒，共同執行同樣的程式與資料(r1的run方法與r1物件的x物件變數)， <br>
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;第6~10行的迴圈共執行4次，二條執行緒若各跑4次，輸出也最多八次，D/E的答案不可能。 <br>
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;A/B/C選二個，觀察x變數，由於二條執行共用此x，所以不管是執行緒1或2只會對x變數增加，輸出應呈現增加的狀況，B基本上不可能。

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