help in garbage collection question

[Amrita Chaurasia]

class C
{
public static void main(String a[])
{
C c1=new C();
C c2=m1(c1);
C c3=new C();
c2=c3; //6
anothermethod();
}
static C m1(C ob1){
ob1 =new C();
return ob1;
}
}
After line 6, how many objects are eligible for garbage collection?


I got this question from examsguide.com free sample questions...
please help

[ankur tyagi]

first an objectod C is created which is referenced by c1.
then c1 is passed into method m() which does nothing but creates another C object that is referenced by c2
and finally a thierd object referenced by c3 is created.
when line c2=c3 is done..
it simply makes c2 refer to the object also referenced by c3..
so there is no reference left to the object that was originally referenced by c2.
so only 1 object is eligible for GC.
hope it helps...

[Amrita Chaurasia]

thanks a lot

[Sidharth Pallai]

ankur tyagi wrote:first an objectod C is created which is referenced by c1.
then c1 is passed into method m() which does nothing but creates another C object that is referenced by c2
and finally a thierd object referenced by c3 is created.
when line c2=c3 is done..
it simply makes c2 refer to the object also referenced by c3..
so there is no reference left to the object that was originally referenced by c2.
so only 1 object is eligible for GC.
hope it helps...

I dont think your answere is correct. After line#6 there are no objects eligible for garbage collection. Ref. variables c1,c2,c3 are still refrencing C object.

[Ankit Garg]

I dont think your answere is correct. After line#6 there are no objects eligible for garbage collection. Ref. variables c1,c2,c3 are still refrencing C object.

Well there is 1 object eligible for GC. The explanation is correct. c1,c2 and c3 do refer to an object of class C, but the object that c2 pointed to originally will be eligible for GC...

[Sidharth Pallai]

Yes Ankit, you are correct, i was just misunderstood.

The object which got created inside the static method lost its reference to c3, which inturn pointing to a different C object.

[nav katoch]

class C 
{ 
public static void main(String a[]) 
{ 
C c1=new C(); 
C c2=m1(c1); 
C c3=new C(); 
c2=c3; //6 
anothermethod(); 
} 
static C m1(C ob1){ 
ob1 =new C(); 
return ob1; 

} 
}

I just arranged it for a better view.

Naveen

[Ulrika Tingle]

Amrita Chaurasia wrote:
After line 6, how many objects are eligible for garbage collection?

It's a trick question.

You don't know because you don't know how many eligible objects have already been GCed.

[Bert Bates]

Ulrika,


Please explain your idea about it being a trick question!

Thanks,

Bert

p.s. I don't think it is, because that's how Sun tends to phrase this kind of question, but maybe you've got an insight here...

[rajanishhh pillai]

Hi ranches,

There will possibly be two objects that will be getting garbage collected, c1 and c2 (old reference,obj1) will be the unlucky ones.

class C
{
public static void main(String a[])
{
C c1=new C(); // A new reference is created for C and referred to c1
C c2=m1(c1);  // c2 will be referred by the new instances returned by ob1 , now c1 is eligible for GC
C c3=new C(); // c3 is referred by the new instances
c2=c3; //6    // now c2 is referring c3 so c2's reference is eligible for GC , Now c2 and c3 have same reference.
// c1 and c2's old reference will be eligible for GC.
anothermethod();
}
static C m1(C ob1){
ob1 =new C();  // ob1 which was previously referring c1,releases it and creates a new reference
return ob1;
}
} 

Cheers
Rajanish