SCJP 1.6版考題 120

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

解答

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Ans: D

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。