Interfaces in C#: An Easy Learning

An easy-to-follow guide to interfaces in C#, covering what they are, how to implement them, and why they matter.

What is an Interface?

An interface defines a contract of members, such as methods and properties, that any implementing class must provide, without specifying how those members work internally.

Declaring an Interface

Interfaces are declared using the interface keyword, and by convention their names start with a capital I, such as IShape or IComparable.

Implementing an Interface

A class implements an interface by listing it after a colon and then providing concrete implementations for every member the interface declares.

Why Use Interfaces?

Interfaces enable loose coupling between components and allow a single class to support multiple contracts, which is especially useful for testing and for designing flexible, extensible systems.