GC program needs explanation

[priyadharshini vijayaraghavan]

class A{
A aob;
public static void main(String args[]){
A a=new A();
A b=new A();
A c=new A();
a.aob=b;
b.aob=a;
c.aob=a.aob;
A d=new A().aob=new A();
c=b;
c.aob=null;// line1
System.gc();
}
}

Question is how many objects are available for GC after line1;

Output is 2. Can anybody explain this to me

[Janeice DelVecchio]

Please QuoteYourSources when posting questions

[Hemnathbabu Kottaiveedu]

Hi Priyadarshini,

can you please tell us what is the answer as per your understanding?

I believe that the answer which you have mentioned is not correct.

Thanks,
Hemnath

[micha koern]

I think 2 is correct.

class A {
	A aob;

	public static void main(String args[]) {
		A a = new A();
		A b = new A();
		A c = new A();
		a.aob = b;
		b.aob = a;
		c.aob = a.aob;
		A d = new A().aob = new A();
		c = b;
		c.aob = null;// line1
		System.gc();
	}
}

- First you create 3 Objects and their 3 references a b c:

A a = new A();
A b = new A();
A c = new A();

- than you link the objects:

a.aob = b;
b.aob = a;
c.aob = a.aob;

After this one Object is referenced by a and b.aob.
one Object is referenced by b and a.aob
one Object is referenced by c


Than they try to get you confused:
- 2 Objects are created.
- The First gets a reference to the Second
- After this d gets the result of this operation (The result of the assignment is the assigned Object- so the 2nd Object is reffered)
- the First Object is available for the gc

A d = new A().aob = new A();

Now they set

c = b;

So the Object referenced by c is now ready for the GC (it now also references the Object that is referenced by b and a.aob)


This is senceless:

c.aob = null;

Because there is another reference to the Object (a)

[priyadharshini vijayaraghavan]

Hi

I forgot the place from where I got this program... coz i was searching for GC related questions in internet.
I thought i understood GC very well and so i wanted to test myself, but unfortunately I found this one very difficult to solve. I got confused.

I thought only the object referenced by c will be eligible for GC.

but now I understood.

Thanks micha

It was a good explanation.

[Hemnathbabu Kottaiveedu]

Very well explained Micha!!. I agree with you.

Thanks,
Hemnath