What is Abstract class in C#?

In today's post i am going to cover "What is Abstract class in C#  "? and later we understand the diffrence between Abstract class and Interface.

Abstract Class

Abstract class is a class which can not be instantiated.It means object creation for that class is not possible.The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share.(To improve the functionality of the method).

A class is marked with abstract keyword to declared as abstract class.Below is the simple example of abstract class.

Abstract class can contain either non-abstract method(concrete method) or abstract method.Abstract members do not have any implementation in the abstract class, but the in derived class it should be implemented.

Key points to remember:

• An abstract class can have abstract member as well as non-abstract method (concrete method).
• Abstract keyword is used to declare the method as abstract in abstract class.
• A class can inherit more than one interface but only one abstract class.
• An abstract class can have public, protected, static methods, but the abstract method in abstract class cannot be static.
• An abstract method cannot be private.
• An abstract method cannot have the modifier virtual because an abstract method is implicitly virtual.
• The access modifier of abstract method should be same in both the abstract class and derived class.
• When a class contains at least one abstract method, then the class must be declared as abstract class.
• It is mandatory to override abstract method in derived class.

Abstract methods have no implementation, so the method definition is followed by a semicolon instead of a normal method block. Derived classes of the abstract class must implement all abstract methods. When an abstract class inherits a virtual method from a base class, the abstract class can override the virtual method with an abstract method. For example:

If a virtual method is declared abstract, it is still virtual to any class inheriting from the abstract class. A class inheriting an abstract method cannot access the original implementation of the method .In the previous example, GetData() on class D cannot call GetData() on class A. In this way, an abstract class can force derived classes to provide new method implementations for virtual methods.

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