Abstract Class in C#
a) Classes can be declared as abstract class by using abstract keyword.
b) Abstract class is designed to act as a base class (to be inherited by other classes).Abstract class is a design concept in program development and provides a base upon which other classes are built.
c) Abstract class does not allow creating instance or object of it; we must inherit to use it, pls. check below fig.
d) Abstract classes can have abstract methods as well as non-abstract methods (which must be implemented in the child class).
e) A non-abstract class derived from an Abstract class must include implementations for all inherited abstract methods.
f) An abstract class cannot be a sealed or static class.
g) An abstract method cannot be private, protected or protected internal.
h) An abstract member cannot be static.