Can abstract class extend concrete class

An abstract class is a class declared with an abstract keyword which is a collection of abstract and non-abstract methods while a concrete class is a class that allows creating an instance or an object using the new keyword. Thus, this is the main difference between abstract class and concrete class.13 May 2019

A concrete parent class cannot force/oblige its children to include/implement a method . An abstract parent class oblige its children to do that by declaring abstract methods.

13.2. 3.2 Each concrete class as a single table. Another approach to represent inheritance is to represent each concrete class as a separate table. Each table would contain the attributes of the concrete class and the attributes of all of its superclasses .