Question

Assume that class B extends from class A.

So what is the advantage of writing something like this:

A myClassA = new B();

What’s the difference to:

B myClassA = new B();

Answer 1

This is the concept of programming to interfaces(or supertype)
we use supertype reference so that it can hold any sub type instance

eg: assume we have Class B & C extending A

& some method which accepts A as parameter

void print(A a) {System.out.println(a);}

this method canbe invoked by passing any instance of A or its subtype