Garbage Collection

[sandhi mridul]

I am not getting this question.

  At what point is the object anObj available for garbage collection.
    
  01:  public class Base{
  02:
  03:   private void test() {
  04:
  05:      if(true) {
  06:         String anObj = "sample";
  07:         String locObj = anObj;
  08:         anObj.trim(); 
  09:         anObj = null;
  10:         locObj.trim(); 
  11:      }
  12:    }
  13:         
  14:    static public void main(String[] a) {
  15:       new Base().test();
  16:   }   
  17:  
  18:  }
 
    Select most appropriate answer
 
    a) After line 7
    b) After line 8
    c) After line 9
    d) After line 10
    e) After line 11  

According to me it should be after line 9 but the answer is after line 11.

Please explain me if the answer is right then why after line 11.

Thanks
Sandhya

[Jeff Rummings]

Look at line 7:

  07:         String locObj = anObj;

The string is still reachable through the locObj reference. Line 11 is correct because all objects become unreachable beyond the if statement.

[marc weber]

This example is a little tricky because the object is a String literal. See Strings, Literally for an explanation.

(My understanding is that garbage collection questions on the real exam will not involve String literals.)

[Sheryl Pinto]

Hi Sandhi,

There is only one String object and that is "sample". anObj is just a reference pointing to "sample".

After line 7, both anObj and locObj point to "sample".
After line 9, reference anObj points to null but locObj is still pointing to "sample" and thus "sample" is not eligible for GC.

Also see:
http://faq.javaranch.com/java/ScjpFaq#stringLiteralGC

Sheryl.

[sandhi mridul]

Thanks Arman I got it.