When to use Interfaces and when o use Abstract Classes

When to use Interfaces and when o use Abstract Classes

 I would say that interfaces are better in many scenarios, but they also lead to code duplication which is a negative thing. If you have a wide array of subclasses which will be doing largely the same implementation, plus extra functionality, then you might want an abstract class. It allows you to have many similar objects with fine grained detail, whereas with only interfaces, you must have many distinct objects with almost duplicate code.

Interfaces have many uses, and there is a compelling reason to believe they are 'better'. However you should always be using the correct tool for the job, and that means that you can't write off abstract classes.

Abstract Classes

1.Cannot be instantiated independently from their derived classes. Abstract class constructors are called only by their derived classes.

2.Define abstract member signatures that base classes must implement.

3.Are more extensible than interfaces, without breaking any version compatibility. With abstract classes, it is possible to add additional nonabstract members that all derived classes can inherit.

4.Can include data stored in fields.

5.Allow for (virtual) members that have implementation and, therefore, provide a default implementation of a member to the deriving class.

6.Deriving from an abstract class uses up a subclass's one and only base class option.

Interface

1.Cannot be instantiated.

2.Implementation of all members of the interface occurs in the base class. It is not possible to implement only some members within the implementing class.

3.Extending interfaces with additional members breaks the version compatibility.

4.Cannot store any data. Fields can be specified only on the deriving classes. The workaround for this is to define properties, but without implementation.

5.All members are automatically virtual and cannot include any implementation.

6.Although no default implementation can appear, classes implementing interfaces can continue to derive from one another.