Duplicate
With C#, when to use Interfaces and when to use Abstract Classes, what can be the deciding factor.
+7
A:
The advantages of an abstract class are
- Ability to specify default implementations of methods
- Added invariant checking to functions
- Have slightly more control in how the "interface" methods are called
- Ability to provide behavior related or unrelated to the interface for "free"
Interfaces are merely data passing contracts and do not have these features. However they are typically more flexible as a type can only derived from one class but can implement any number of interfaces.
JaredPar
2009-04-14 13:21:52
-1? At least add a reason
JaredPar
2009-04-14 13:27:13
@JaredPar : I guess it's to discourage answering duplicate questions (btw, I'm not the one who downvoted you)
Brann
2009-04-14 13:34:25
@Brann, I've unfortunately seen that behavior before. Seems like it would make more sense to use the down vote on the OP. It's their responsibility to search for dupes.
JaredPar
2009-04-14 13:37:09
I'll +1, if memory serves this is what was in the framework design guidelines. Great examples in there too.
JoshBerke
2009-04-14 13:37:26
If you think this is a dup, why have you posted this as a reply? It is more common to vote "dup" and add a comment / edit the OP.
Marc Gravell
2009-04-14 13:28:47
@Rik The question you link to is a language agnostic question while this is C# specific, so while there is a lot of overlap, the answers are not exactly the same. For a good example, see Zifre's answer.
Robert Gowland
2009-04-14 13:32:54
Does it work differently in any other single inheritance language with interfaces?
Rik
2009-04-14 13:41:08
Well there sure is the difference between a normal base class and one marked as "abstract" in C#, a notion other single inheritance languages with interfaces might not have.
Dave Van den Eynde
2009-04-14 13:54:14
+1
A:
The real question is: whether to use interfaces or base classes. This has been covered before.
In C#, an abstract class (one marked with the keyword "abstract") is simply a class from which you cannot instantiate objects. This serves a different purpose than simply making the distinction between base classes and interfaces.
Dave Van den Eynde
2009-04-14 13:24:04
+1
A:
Abstract classes and interfaces are semantically different, although their usage can overlap.
An abstract class is generally used as a building basis for similar classes. Implementation that is common for the classes can be in the abstract class.
An interface is generally used to specify an ability for classes, where the classes doesn't have to be very similar.
Guffa
2009-04-14 13:26:28
+1
A:
Another thing to consider is that, since there is no multiple inheritance, if you want a class to be able to implement/inherit from your interface/abstract class, but inherit from another base class, use an interface.
Zifre
2009-04-14 13:29:37
A:
The best answer I have seen is in this excellent book by Brad Adams and Krzysztof Cwalina
http://www.amazon.com/Framework-Design-Guidelines-Conventions-Development/dp/0321545613
JoshBerke
2009-04-14 13:35:58