Abstract & Interface in C#

#csharp #beginners #learning

Note: We will use a famous example, an Animal, for the whole article

What is Abstract?

Abstract class provide a base define for something (Ex: Base class for Dog and Bird is Animal). It present for Polymorphism in OOP. An abstract class is declared using the abstract keyword. It can contain both abstract methods (without implementations) and non-abstract methods (with implementations). Take a look at example below

We define abstract class Animal with the following detail:

Properties: name
Abstract methods: MoveBy
Non-abstract methods: Print

Next, we will create two classes Dog and Bird which implement Animal. After that, we initialize them

Now we can get some point in here:

Every Dog and Bird have the name (1)
But Dog move by leg and Bird move by wing (maybe by leg also but assume it) (2)

With (1), we can declare Print method in Animal with non-abstract type to use for Dog and Bird

With (2), the MoveBy method must be abstract and it would be declared in each class later. This is the key point to show difference between abstract and non-abstract method.

Summary,

Abstract class provide a base definition (Ex: Animal)
Abstract method provide base method which execute differently for each class implement (Ex: MoveBy)
Non-abstract method are usually use as a common method for all class implementation (Ex: Print)

What is Interface?

For short, an interface is a completely “abstract class” that defines a contract for related functionalities. When we sign a contract, we must provide/do everything defined in a contract, like A must give B 100k$ and don't need to know A give cash or transfer - that is the Abstraction in OOP. Take a look at the example below

We define interface class IAction with the following detail: