Question

Being not a programmer, I would like to understand the following code:

A a=new A();
B a=new B();

a=b;      
c=null;

b=c; 

If the variables are holding only reference, will ‘a’ be null in the end?

Answer 1

You need to divorce two concepts in your mind; the reference and the object. The reference is essentially the address of the object on the managed heap. So:

A a = new A(); // new object A created, reference a assigned that address
B b = new B(); // new object B created, reference b assigned that address
a = b; // we'll assume that is legal; the value of "b", i.e. the address of B
       // from the previous step, is assigned to a
c = null; // c is now a null reference
b = c; // b is now a null reference

This doesn’t impact “a” or “A”. “a” still holds the address of the B that we created.

So no, “a” is not null in the end.