Introduction
In this article along with the demo project I
will discuss Interfaces versus Abstract classes. The concept of Abstract classes and Interfaces is a bit
confusing for beginners of Object Oriented programming. Therefore, I am trying
to discuss the theoretical aspects of both the concepts and compare their
usage. And finally I will demonstrate how to use them with C#.
Background
An Abstract class without
any implementation just looks like an Interface; however there are
lot of differences than similarities between an Abstract class and an Interface. Let's explain both concepts and
compare their similarities and differences.
What is an Abstract Class?
An abstract class is
a special kind of class that cannot be instantiated. So the
question is why we need a class that cannot be
instantiated? An abstract class is
only to be sub-classed
(inherited from). In other words, it only allows other classes to inherit from it but cannot be
instantiated. The advantage is that it enforces certain hierarchies for all the
subclasses. In
simple words, it is a kind of contract that forces all the subclasses to carry on the same
hierarchies or standards.
What is an Interface?
An interface is not a class. It is an entity that is defined by the
word Interface. An interface has
no implementation; it only has the signature or in other words, just the
definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that
is used to define hierarchies for all subclasses or it defines specific set of methods
and their arguments. The main difference between them is that a class can
implement more than one interface but can only inherit from one abstract class. Since C# doesn’t
support multiple inheritance, interfaces are used to
implement multiple inheritance.
Both Together
When we create an interface, we are basically creating a set of
methods without any implementation that must be overridden by the implemented classes. The advantage is that it provides a way
for a class to be a part of two classes: one from
inheritance hierarchy and one from the interface.
When we create an abstract class, we are creating a
base class that might have one or more completed
methods but at least one or more methods are left uncompleted and declared abstract. If all the methods of an abstract class are
uncompleted then it is same as an interface. The purpose of an abstract class is to provide a base class definition for how a set of derived classes will work and then allow the programmers
to fill the implementation in the derived classes.
