Abstract class & Interface

David Smith

1.What is the difference between an abstract class and interface. I am still lost when it comes to explaining this to someone.

2. When to use abstract class?

3. When to use an interface?

12 Replies

Know the answer? Post it — somebody with the same question will find it here.

Munesh Sharma11y ago
· Abstract class can have implementation for some of its method. But the interface can't have implementation for any of its method.
· Abstract class can have field but interface does not have fields.
· An Interface can inherit from another interface only can't inherit from another abstract class but an abstract class can inherit from another abstract class and another interface.
· Abstract class members can have access modifiers where interface member doesn't have access modifiers.
Rajeesh Menoth11y ago
Hi,

An abstract class is a special kind of class that cannot be instantiated. So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.

Reference :

http://www.aspdotnet-suresh.com/2010/04/abstract-versus-interface.html
David Smith11y ago
Could you please answer the question on this thread.
Munesh Sharma11y ago
http://www.c-sharpcorner.com/UploadFile/annathurai/abstract-class-in-C-Sharp/
Munesh Sharma11y ago
http://dotnet-munesh.blogspot.in/2015/09/interface-in-c.html
David Smith11y ago
What do it mean when they say an abstract class is a special type of class in which you can have members without implementation, and how is that difference from interface?
David Smith11y ago
So I understand what an interface is now, so what makes an abstract class different from interface. In both the interface and abstract class you still have to implement members.
Rajeesh Menoth11y ago
Hi David Smith,

An interface looks like a class, but has no implementation. The only thing it contains are declarations of events, indexers, methods and/or properties. The reason interfaces only provide declarations is because they are inherited by classes and structs, which must provide an implementation for each interface member declared.

Reference :

http://www.csharp-station.com/Tutorial/CSharp/Lesson13
Maha11y ago
2. When to use abstract class?

Sometimes a parent class is so general that you never intend to create any specific instances of the class. For example, you might never create "just" an Artist; each Artist is more specifically a Painter, Sculptor, Illustrator, and so on. A class that you create only to extend from, but not to instantiate from, is an abstract class.

3. When to use an interface?

Multiple inheritances are not allowed in C#. In order to meet such a requirement Interfaces are used.
David Smith11y ago
I have been through many examples. I am still not able to explain the difference. So instead can you just explain the difference. I do know the commonality of an abstract class and interface class
Nilesh Jadav11y ago
Hey David !

Check this link to know the difference :

1) http://www.aspdotnet-suresh.com/2010/04/abstract-versus-interface.html
2) http://www.c-sharpcorner.com/uploadfile/prasoonk/abstract-class-vs-interface/

Check this link to know when to use abstract class and when to use interface:

1) http://programmers.stackexchange.com/questions/41740/when-to-use-abstract-classes-instead-of-interfaces-with-extension-methods-in-c

Thank you
Manas Mohapatra11y ago
Please go through below links that might help you:

http://www.codeproject.com/Articles/11155/Abstract-Class-versus-Interface

https://msdn.microsoft.com/en-in/library/scsyfw1d(v=vs.71).aspx