abstract class and interface

This codeproject article will explain it to you:

Abstract Class versus Interface[^]

Interface

Basically there is no implementations in an Interface.While we using an interface , you should implement the methods/properties inside your class.i.e;an interface method is doing nothing until you implemented in your class.The implementation class is responsible for the total implementation in case of an interface.

Abstract class

An absract class is a base class that behaves like a normal class except these have no independent existance, i.e;it is not possible to create an instance of an abstract class directly.The instance can be created using the derived class only.The methods/properties may/mayn't be implemented in the derived class except for abstract members.The abstract members should be implemented in the derived class.

Thus an interface looks similar to an abstract class with only abstract members.

public abstract class SampleAbstract
 {
   public abstract void Show();
   public abstract void Calculate();
 }

is almost similar to

public interface SampleInterface
  {
    void Show();
    void Calculate();
  }

My biggest problem with interfaces actually has something to do with Visual Studio rather than structure itself.

If you right click and "Go to Definition" in any class that inherits from an interface, you go to the interface, not the class you really wanted to see. Then you end up doing a global search for the inherited class. This annoys me.

But there is the one advantage to interfaces: If you inherit from an interface, you can inherit from the inherited class. If you use an abstract class, you can only inherit once.

If you want a hard and fast scenario, I would say this: if you are developing a commercial DLL that a user will implement, or you know the general structure of what you are planning, but not how it will be fleshed out, then use an interface.

If you have a good idea of what you want and you don't plan on inheriting that class more than once, use an Abstract class.

Ryan McBeth