Garbage collection

[Henry Zhi Lin]

Guys,

this is from devaka's examlab, practice 1, question 68.

   1.  public class Aegis{
     2.       Aegis ags=null;
     3.       public static void main(String argv[]){
     4.            Aegis a1=new Aegis();
     5.            Aegis a2=new Aegis();
     6.            Aegis a3=new Aegis();
     7.            a1.ags=new Aegis();
     8.            a2.ags=a1.ags;
     9.            a3.ags=a2.ags;
     10.           a1=null;
     11.           a2=null;
     12.           a3=null;
     13.      }
     14. }

the answer is after line 9 we have only one object eligible to GB.

Can anyone draw a diagram for me I am confused here again?

[Henry Wong]

Can anyone draw a diagram for me I am confused here again?

Instead of just trusting the answer, can you tell us what you think the answer should be? After all, I am assuming that you are confused here because you think the answer is something else?

(hint: I don't agree with the answer either)

Henry

[Henry Zhi Lin]

Herny,

the following is what I thought,

after line 6
a1 ---> OA
a2 ---> OB
a3 ---> OC

after line 7
a1 ---> OA --> OD
a2 ---> OB
a3 ---> OC

after line 8
a1 ---> OA --> OD
a2 ---> OB --> OD
a3 ---> OC

after line 9
a1 ---> OA --> OD
a2 ---> OB --> OD
a3 ---> OC --> OD

after line 10
a2 ---> OB --> OD
a3 ---> OC --> OD
which OA should be eligible to GB, so my answer is after line 10 not line 9.

[Devaka Cooray]

Hi Henry Zhi Lin,

Please do not post misleading statements here. You said .....

Originally posted by Henry Zhi Lin:

...the answer is after line 9 we have only one object eligible to GB...

But in my simulator, the correct answer as given is "line 10" (Answer D)! However another time you said,....

Originally posted by Henry Zhi Lin:

...so my answer is after line 10 not line 9....

So, if both you and me said that the correct answer is line 10; then who said, the answer is after line 9?

Due to your posts, others may think that the questions/answers in my simulator are not accurate; as you can see below:

Originally posted by Henry Wong:

hint: I don't agree with the answer either

Because of this, please feel kind to correct this as soon as possible.

Devaka.

[Henry Zhi Lin]

Sorry Devaka, I guess I must misread your answer. I have a suggest on your simulator, would you mind to add save test result function, currently after I exit your simulator everything will not be saved.

Thanks anyway!

[Fabio Nascimento]

a1 ---> [Aegis]
a2 ---> [Aegis]
a3 ---> [Aegis]
 
a1.ags ---> a2.ags ---> a3.ags ---> [Aegis]

After line 10

a1      [Aegis]
a2 ---> [Aegis]
a3 ---> [Aegis]
 
a1.ags ---> a2.ags ---> a3.ags ---> [Aegis]

After line 10 you have one Aegis Object eligible for GC, after all you have 4 objects eligible for GC, three that you removed the references manually and one that become unreachable after that.

[Rekha Srinath]

All,

Sometimes I get confused on such situations...

In this code, the 'ags' of a1 is pointing to another Aegis object (lets call it X). Ok..

Now when a1 is made null, there is no meaning for a1.ags, right? which means that object X cannot be reached via a1.ags.

So, if I have the code as:
Aegis a1=new Aegis();
a1.ags=new Aegis();
a1 = null; // Line 1

After Line 1, there are two objects eligible for GC, right?

Please correct me if I am wrong.

[James Tharakan]

@ Rekha Srinath

Hope the following tell you are Right

class fun
{   
    fun f1;
    String name;
     fun(String s)
     {
         this.name=s;
     }
             
    public static void main(String args[])
    {
         fun f= new fun("James");
         f.f1=new fun("Games");
         f=null;
         System.gc();
         
    }
    
  public void  finalize()
   {
       System.out.println(this.name);
   }
}

Output:
Games
James
[ November 19, 2008: Message edited by: James Tharakan ]

[Rekha Srinath]

That was a cool example James !!

[Jyothsna Panchagnula]

Hi James,

Can we say that Fun f and f.f1 are the objects that are garbage collected. ?

thanks,
Jyothsna

[James Tharakan]

Yes the objects refered BY f anf f.f1

[Edmen Tay]

So, if I have the code as:
Aegis a1=new Aegis();
a1.ags=new Aegis();
a1 = null; // Line 1

So, Can we said that when object reference a1 point to null, then its instance variable reference(a1.ags) will be set to null as well. Am I right?

Please correct, if i am wrong.

Thanks

Regards,
Edmen