檢視 SCJP 1.6版考題 120 的原始碼

 Given:
 1. public class GC{
 2.   private Object o;
 3.   private void doSomethingElse(Object obj){o = obj;}
 4.   public void doSomething(){
 5.     Object o = new Object();
 6.     doSomethingElse(o);
 7.     o = new Object();
 8.     doSomethingElse(null);
 9.     o = null;
 10. }
 11.}
 When the doSomething method is called, 
 after which line does the Object created in line 5 become available for garbage collection?
   A. Line 5
   B. Line 6
   C. Line 7
   D. Line 8
   E. Line 9
   F. Line 10

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

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

<span style="font-size:medium;"> 解說:
 方法變數o指向第5建立的物件在第6行方法doSomethingElse執行時，被GC物件的o參考，
 即使第8行方法變數o指向新的物件也還是被參考住而不是垃圾物件的候選，
 直到再次呼叫doSomethingElse方法，將GC物件的o設為null，第5行建立的物件就沒有指向。

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{{SCJP 1.6版考題講解}}