檢視 SCJP 1.6版考題 242 的原始碼

Given:
<br>
public class NamedCounter{
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   private final String name;
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   private int count;
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   public NamedCounter(String name){this.name = name;}
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   public String getName(){return name;}
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;  public void increment(){count++;}
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   public int getCount(){return count;}
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;   public void reset(){count = 0;}
<br>}
   
<br>Which three changes should be made to adapt this class to be used safely by multiple threads? (Choose three.) 
<br>
<br>A. declare reset() using the synchronized keyword
<br>B. declare getName() using the synchronized keyword
<br>C. declare getCount() using the synchronized keyword
<br>D. declare the constructor using the synchronized keyword
<br>E. declare increment() using the synchronized keyword


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

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

<span style="font-size:medium;"> 解說:
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;題目問那三個改變應該被做出來，以調整這個類別可以在多執行緒的環境上被安全地使用？
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<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;多執行緒使用類別中的變數若有變更的情況，應該對所有這個變數的存取(讀或寫)方法以同步的方式設定。
<br>&nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;此題count在reset與increment方法有被變更值的情況，因此連同getCount這三個方法都要變成同步的方法。
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{{SCJP 1.6版考題講解}}