Interfaces in oops

yes, i am working on C#,

i am unable to understand "as-is", can u please give example.

Thanks
Tyr

I do not use C#. The above "as is" is not a term, just the result of my poor English. I can only explain you the meaning (based on my C++ experience plus some info from C# reference).

In C#, you can use "abstract" modifier of the method declaration (http://msdn.microsoft.com/en-us/library/sf985hc5.aspx).  This way you express the fact that the method is not implemented. It also means that you cannot create an instance of the class (because the object would not be able to use that unimplemented method).

This also means that having only definition of the abstract class (the source files in C++ terms, or some bytecode that represents the abstract class in C#) is not enough to be able to use it. You have to use the abstract class as the base class of another, your, derrived class, and you have to implement the abstract methods. Still, you are forced to keep the method signature the same. (You use the override modifier.)

In C++, pure virtual methods are used in the role of abstract methods. In C#, you have the above mentioned specific keywords for that.

When the base class is written by someone else and the derived class is written by you, then the abstract method signature (i.e. the name, arguments and their types) is a way of forcing you to keep the way how the method will be called. If all methods in the C++ abstract base class are pure virtual (i.e. without implementation) and the class does not define any data member, then the abstract class has the features that are called "interface" elsewhere.

In C#, the interfaces are basically the same, only the syntax is simpler. The same way, you derive from the interface and you must implement its method. But the interface ensures that your implementation must be called the way that was enforced by the author of the interface.

For an interface, a base class, and multiple inheritance.... The multiple inheritance is not that big problem if the base classes do not have data members and if they use virtual methods. In such cases, it is also easy to replace the multiple inheritance by the chain of base classes using the single inheritance. This is why other languages may not want allow multiple inheritance, but allow you to use more than one interface (which is equivalent of multiple inheritance from more than one abstract classes.

Well, I may not to express some details clearly. Someone else can adds his/her view. ;)

Pepr i also worked on the c++ and understand you. but in view of c# it is really different so anybody from java or c# background please resolve my query.