.What is Abstract Class?

The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class.

• An abstract class cannot be instantiated. The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share.
• Abstract classes may also define abstract methods. This is accomplished by adding the keyword abstract before the return type of the method.
• Abstract methods have no implementation
• 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.
• An abstract class must provide implementation for all interface members.
• An abstract class that implements an interface might map the interface methods onto abstract methods.
• A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.