Question

In Java, I have parent class P and a child class C.

In an abstract class, I have a method void blah(P parent). In a child class of the abstract class, it doesn’t compile by having void blah(C child).

How do I achieve the type check in the child class?

Answer 1

void blah(P parent) and void blah(C child) are actually different methods. That’s why you can not use the C Child to override an abstract P parent method.

So, in your child class of the abstract class, you can either

void blah(P parent){
  if(parent instanceof C){
     ...
  }else if(parent instanceof C2){

  }
}

Or just implement these two methods separately.