answer to sun sample question

[abhishek]

what will be the answer to the following question?
Given:
public class X {
public void m(Object x) {
x = new Integer(99);
Integer y = (Integer)x;
y = null;
System.out.println("x is" + x);
}
}
When is the Integer object, created in line 3, eligible for garbage collection?
never
just after line 4
just after line 5
just after line 6 (that is, as the method returns)
when the calling method sets the argument it passed into this method to null

[Rajiv Ranjan]

I think the answer is
just after line 6 (that is, as the method returns)
Thanks.

[Ajith Kallambella]

'abhishek',
PROPER NAMES ARE NOW REQUIRED!! and your name doesnot comply with the official naming policy.
Please read this post for more details and register again with a valid name.
Ajith

[saumil shukla]

Hi,
Since Objects are passed by reference and not by value, even when the method returns the Object created in line 3 will still be reffered by the Object x passed on when calling the method. Till the calling reference is not set back to null, I think this object can not be GC.
Thanks

Originally posted by abhishek:
what will be the answer to the following question?
Given:
public class X {
public void m(Object x) {
x = new Integer(99);
Integer y = (Integer)x;
y = null;
System.out.println("x is" + x);
}
}
When is the Integer object, created in line 3, eligible for garbage collection?
never
just after line 4
just after line 5
just after line 6 (that is, as the method returns)
when the calling method sets the argument it passed into this method to null

[Rajiv Ranjan]

I totally agree with Saumil, but with the exam point of view I think the most suitable answer is :
just after line 6 (that is, as the method returns)

[Cristi Tudose]

Saumil,
u are right but...it's wrong if we think that
reference x that points to object new Integer(99) vanishes
when the method return(the scope of x is the scope of m) ???
So,the answer it's :just after line 6 (that is, as the method returns)
rgds,
Cristi
------------------

[Vlad G]

Guys,
If you didn't know the one and only parameter passing mechanism Java uses is pass by value. In case of primitives the primitive value is passed by value, in case of references - refernce to an object is passed by value (not the object of course, so this creates a misconception that Java passes parameters by reference in case of objects). You were right, Integer(99) is a candidate for GC after line 6. To add, assignments to x within this method do not affect the reference that x was copied from, so if I call m like this:
<pre>
Object y = new X();
y.m(y);
</pre>
y will point to object of type X all the time, even after line 3 in m is run.
Vlad.

[Cristi Tudose]

Vlad,
do u think,your piece of code is a valid one???
I don't,but i get what you want to say...
Object y = new X();
y.m(y);
rgds,Cristi

[abhishek]

Thanks everybody for the answers.
abhishek p.

[Vlad G]

Well, I made a small mistake (forgot about type cast), but in general my fragment of code is syntactically correct. The following compiles and runs OK:
<pre>
public class Dumb
{
Dumb()
{
Object y = new X();
((X) y).m(y);
}
public static void main(String[] args)
{
new Dumb();
}
class X
{
public void m (Object x)
{
System.out.println("In m");
}
}
}
</pre>
-VG.