Abstract classes v/s Interfaces

This article explain the scenerios when to use abstract classes and when interfaces.

Use an abstract class

1. Use an abstract class to define a common base class for a family of types.


2. Use an abstract class to provide default behavior.


3. When creating a class library which will be widely distributed or reused—especially to clients, use an abstract class in preference to an interface; because, it simplifies versioning.


4. Subclass only a base class in a hierarchy to which the class logically belongs.

Use and Interface

1. When creating a standalone project which can be changed at will, use an interface in preference to an abstract class; because, it offers more design flexibility.


2. Use interfaces to introduce polymorphic behavior without subclassing and to model multiple inheritance—allowing a specific type to support numerous behaviors.


3. Use an interface to design a polymorphic hierarchy for value types.


4. Use an interface when an immutable contract is really intended.


5. A well-designed interface defines a very specific range of functionality. Split up interfaces that contain unrelated functionality.