arindam.mallik

 Profile Answers by arindam.mallik 

• Oct 30th, 2006

 

The decision tree for this is pretty detailed. :) In most cases, using an abstract class is the "right" thing to do if you're trying to create a common class from which others will derive and which isn't fully specified. Interfaces are nice if you don't want to force classes to have a single root class in their hierarchy, as a single class can implement multiple interfaces. Concrete classes should be used if it's fully specified--i.e. subclasses don't have any hooks into which they must provide functionality.

kiran

• Dec 24th, 2006

 

Interface - used to define a skeleton. Classes who want to confirm to that skeleton implementsts the interface

Abstract class - Use abstract class when you want to provide some functionality to the user and at the same time would like to enforce some skeleton (structure) for the users of your class

Concrete class - Use a concrete class to represent an object (data & methods) which can be extended or reused.

saurabhd

 Profile Answers by saurabhd 

• Jan 19th, 2007

 

Use following guidelines for each of the abstractions:

Interface:
-- If your child classes should all implement a certain group of methods/functionalities, but each of the child classes is free to provide its own implementation, then use interfaces.
For e.g., if you are implementing a class hierarchy for vehicles, implement an interface called "Vehicle", which has properties like Colour, MaxSpeed etc., and methods like Drive(). All child classes like "Car", "Scooter", "AirPlane", "SolarCar" etc. should derive from this base interface, but provide a seperate implementation of the methods and properties exposed by Vehicle.
-- If you want your child classes to implement multiple, unrelated functionalities, in short multiple inheritance, use interfaces.
For e.g., if you are implementing a class called "SpaceShip", that has to have functionalities from a "Vehicle", as well as that from a "UFO", then make both "Vehicle" and "UFO" as interfaces, and then create a class "SpaceShip" that implements both "Vehicle" and "UFO".

Abstract Classes
-- When you have a requirement where your base class should provide default implementation of certain methods, whereas other methods should be open to being overridden by child classes, use abstract classes.
For e.g., again take the example of the "Vehicle" class above. If we want all classes deriving from "Vehicle" to implement the "Drive()" method in a fixed way, whereas the other methods can be overridden by child classes. In such a scenario, we implement the "Vehicle" class as an abstract class with an implementation of "Drive", while leave the other methods / properties as abstract so they could be overridden by child classes.
-- The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share. For example, a class library may define an abstract class that is used as a parameter to many of its functions, and require programmers using that library to provide their own implementation of the class by creating a derived class.