What is exact difference between Inheritance and Abstract class?

Question

I know the fundamentals of OOP concepts[Inheritance, Abstraction, Encapsulation, Polymorphism]

We use Inheritance in case of Parent-Child relationship[C

Answer 1

With inheritance you don't need to override a method. Without overriding getROI in Child you could still call new Child().getROI() and get 0 as response.

If on the other hand a method is abstract, it will need to be implemented by the child as there is no default implementation.