abstract method use vs regular methods

Question

I would like to know the difference between two conventions:

1. Creating an abstract base class with an abstract method which will be implemented later on the der

Answer 1

In the case 1) you can access those methods from the abstract base type without knowing the exact type (abstract methods are virtual methods).

The point of the abstract classes is usually to define some contract on the base class which is then implemented by the dervied classes (and in this context it is important to recognize that interfaces are sort of "pure abstract classes").