garbage collection eligibility

[shashank dwivedi]

class A{
A()
{
System.out.print("Inside A");
}
}
class B extends A{
B()
{
System.out.print("Inside B");
}
}
class GcDemo
{
public static void main(String args[])
{
B b1=new B();
B b2=new B();
b1=b2;
}
}

how many objects are eligible for garbage collection and why?

[James Boswell]

shashank

Why don't you tell us what you think the answer is?

[Md. Minhajur Rahman]

Hello shashank , Those Objects are eligible for garbage collection which are not accessible by any active reference. According to your program, at which line you want to count Objects eligible for garbage collection? You have created two object inside main funtion() and inside main() all are accessible. If once you come to outside the main function(), then this two will be eligible for garbage collection.

[James Boswell]

This isn't my program.

[Mittal Vishal]

Shashank,

I guess you are asking for the objects eligible for garbage collection after the line 19 is executed.
And the answer is 1 because only those Objects are eligible for garbage collection which are not accessible by any active reference.
As per your program, you have created 2 objects at line 17 & 18 but after assigning b2 to b1, original b1 object does not have any active reference so it will be eligible for garbage collection

Thanks
Vishal

[shashank dwivedi]

James Boswell wrote:shashank

Why don't you tell us what you think the answer is?

well i think it should be 2.The reason why i think this is because i have created objects of child class
which should call constructor of its parent class.
One object dies here should mean two objects eligible for garbage collection.
I am not sure though if i am right..
please help!

[shashank dwivedi]

shashank dwivedi wrote:

James Boswell wrote:shashank

Why don't you tell us what you think the answer is?

well i think it should be 2.The reason why i think this is because i have created objects of child class
which should call constructor of its parent class.
One object dies here should mean two objects eligible for garbage collection.
I am not sure though if i am right..
please help!

And ofcourse i am talking after line 19.

[Md. Minhajur Rahman]

After line 19, i think 2 objects are eligible.

[Pondurai Singh]

In above code, two objects of type B are created at lines B b1=new B(); and B b2=new B(); . But b1=b2; b2 references the same object as b1 and both are thus again aliases. The object originally referenced by b2 now becomes eligible for garbage collection.

So, in both cases, b1 and b2 point to the same object and any changes done to that object will be seen through both the references. Keep in mind that b1 and b2 are not the object themselves but only references to that object. b1=b2 doesn't copy any values from one object to the other, it simply repoints the reference.

[shashank dwivedi]

Md. Minhajur Rahman wrote:After line 19, i think 2 objects are eligible.

Nobody told me if my thought process is right?

[Henry Wong]

shashank dwivedi wrote:
well i think it should be 2.The reason why i think this is because i have created objects of child class
which should call constructor of its parent class.
One object dies here should mean two objects eligible for garbage collection.
I am not sure though if i am right..
please help!

Just because two constructors are called to initialize the object, doesn't mean that two objects were instantiated. BTW, using the same argument, since class A subclasses from the Object class, aren't three constructors call?

Henry

[Henry Wong]

shashank dwivedi wrote:

shashank dwivedi wrote:

James Boswell wrote:shashank

Why don't you tell us what you think the answer is?

well i think it should be 2.The reason why i think this is because i have created objects of child class
which should call constructor of its parent class.
One object dies here should mean two objects eligible for garbage collection.
I am not sure though if i am right..
please help!

And ofcourse i am talking after line 19.

IMO, I guess it depends on what you mean by "after line 19". If you mean, exactly after execution, and the "b1" local variable is still in scope, then one object is eligible for GC. If you mean, the next line of code, where the main() method completes, and the "b1" and "b2" variable are no longer in scope, then two objects are eligible for GC.

Henry