Garbage Collection in Java

[Jay Shukla]

    
class Cardboard{
Short story = 5;
Cardboard go(Cardboard cb){
cb = null;
return cb;
}
 
public static void main(String args[]){
Cardboard c1 = new Cardboard();
Cardboard c2 = new Cardboard();
Cardboard c3 = c1.go(c2);
c1 = null;
//do stuff
}
 
Ans: 2
 
Explanation given in book: 
 
Only one Cardboard object (c1) is eligible, but it has an associated Short wrapper object that 
is also eligible.
------------------
 

Hoe only 2 objects can be eligible along with those two c3 is also becoming null so can't it 
be null and along with c3 asso. Short will also be deleted.
 
These wat total 4 objects should be deleted.
 

 
I know Ans given above(2) is correct.
 
Can anyone please explain me?
 
Thanks in advance.
 

 

[Henry Wong]

Please Quote Your Sources.


For example, if you had quoted K&B, we would have mentioned that there is something in the Errata related to this very question.

Thanks,
Henry

[Henry Wong]

Hoe only 2 objects can be eligible along with those two c3 is also becoming null so can't it be null and along with c3 asso.

And BTW, "c3" was never assigned an object. So, how does assigning it to null make something eligible for GC. Remember, objects are elible for GC -- not references.

Henry

[Jay Shukla]

Thanks Henry!!!

But how Short is eligible.
Does it automatically perform "Boxing" Internally!!!???

[Henry Wong]

But how Short is eligible.

In the version that you shown, the object is not eligible for GC. In the correct version (version in the Errata for the book), the object is eligible for GC.

Does it automatically perform "Boxing" Internally!!!???

You are assigning a primative value to a wrapper reference. Of course, autoboxing applies -- it's either that, or a compilation error.

Henry
[ November 30, 2008: Message edited by: Henry Wong ]

[Jay Shukla]

Henry i'm really confuse!!!

If there is an errata in the book. The version is got Java 5.

Then what should be the correct answer?

Thanks.

[Henry Wong]

http://www.coderanch.com/t/257589/java-programmer-SCJP/certification/SCJP-Errata-Updated

[Henry Wong]

Then what should be the correct answer?

As you have the question written? One object is eligible for GC.

As written in the Errata? Two objects are eligible for GC.

Henry

[Jay Shukla]

Thanks a lot Henry!!!