Know the runtime class

Hi,
I am creating a cross reference of classes.
If the classes have direct relations then I get all the related classes.
If there is an object of an interface that will be assigned the value of
the implementing class then I am not able to get that class as one of
the references.

For example: class B implements Interface A.
In another class C, I have an object of A. Using reflection, I have
created the object of B and assigned to object of A. 

Now, when I run my program to check the cross references for class C, I
do not get class B in the list as it is not directly involved with class
C.

Is there any way to know the instance of the object of A in the class C?
Which API method should I use for this?

Any help is deeply appreciated.

Thanks
Srikanth