SCJP 1.6版考題 099

3. interface Animal{void makeNoise();}
4. class Horse implements Animal{
5.   Long weight = 1200L;
6.   public void makeNoise(){System.out.println("whinny");}
7. }
8. public class lcelandic extends Horse{
9.   public void makeNoise(){System.out.println("vinny");}
10. public static void main(String[] args) {
11.   Icelandic i1 = new lcelandic();
12.   Icelandic i2 = new lcelandic();
13.   Icelandic i3 = new lcelandic();
14.   i3 = i1; i1 = i2; i2 = null; i3 = i1;
15. }
16.}


When line 14 is reached, how many objects are eligible for the garbage collector?
  A. 0
  B. 1
  C. 2
  D. 3
  E. 4
  F. 6

解答

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Ans: C

解說:

i3=i1，i3原本指向的物件可回收，i1=i2， 
i1原本指向的物件因被i3參考不能被回收，i2=null，
i2指向的物件被i1參考不能回收，i3=i1，i3指向的物件可回收
可以畫圖來看比較清楚。