Sunday, June 4, 2006

What's the difference between Abstract classes and Interfaces?

Features                                      Interfaces                                abstract class

Multiple inheritanceA class may inherit several interfaces.A class may inherit only one abstract class.
Default implementationAn interface cannot provide any code, just the signature.An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access ModfiersAn interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as publicAn abstract class can contain access modifiers for the subs, functions, properties
Core VS PeripheralInterfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface.An abstract class defines the core identity of a class and there it is used for objects of the same type.
HomogeneityIf various implementations only share method signatures then it is better to use Interfaces.If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.
SpeedRequires more time to find the actual method in the corresponding classes.Fast