Question { 18100 }

Tell me the scenario,Where we can use interfaces or
Abstract class.And What is the difference between
interfaces and abstract class?

Answer

In relation to C# (not C++):
1. Interfaces are like abstract class where all member
functions as abstract but cannot have any data members,
constructors or destructors. Classes using interfaces are
forced to implement all the methods in the interface.
2. Does not implement any methods. ie only used as a
template for derived classes to use.
3. All members of interface are public. ie in Interface you
only have to state long Function(); but in a class you have
to state public abstract long Function();
4. A class can have multiple inheritence with an interface
but not a class.
5. Also structures in C# cannot inherit from other classes
of structures but can implement an interface allowing you
to implement more features to your class.
By using interfaces you are not making any assumptions
about the functionality. You want to make sure your classes
using the interfaces implement the functionality of all the
methods in your Interface.
With all above in mind you can probably find more uses for
an interface.
One example: You have many forms of communication like
FileIO or database or IPC. All these forms of communication
will need to features like Open and Close either a file or
a connection Read or write etc. You would then define an
interface with these features for your concrete classes.
You can then use the Interface as a base class pointer like
in C++ to access the derived class's functions.