SCJP題庫第120題

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

 

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。