Interface Definition

Expand your knowledge of .NET types by learning about interfaces.

Interfaces are types that define functionality without any implementation. They describe the necessary methods and properties for a type implementing the interface.

We can think of interfaces as contracts. If our class is implementing an interface, it must have all members the interface defines.

Creating interfaces

Interfaces are reference types. They’re defined in the same way as classes, but use the interface keyword. Just like classes, they’re internal by default. We can mark an interface as public if we want it to be accessible to the external code.

public interface MyInterface

Additionally, although we can name our interfaces any way we want, it’s considered good practice to begin interface names with the letter I. It makes it easier for us to distinguish between interfaces and other types:

public interface IVehicle

Interface members

Interfaces can define the following set of members:

  • Properties
  • Methods
  • Events
  • Indexers

Note: Beginning with C# 8.08.0, interfaces can also define static members and constants.

Let’s build on the IVehicle interface we created earlier:

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