C# Interfaces

What is an Interface?

An interface is a contract that defines what methods a class must have.

It does not contain full implementations (in basic usage), only method definitions. Classes that implement the interface must provide the actual logic.

Why Use Interfaces?

Interfaces allow different classes to follow the same structure while having different implementations.

• Promotes code flexibility
• Supports abstraction
• Allows multiple behaviors
• Used heavily in real-world applications

Implementing an Interface

A class implements an interface using the : symbol.

The class must provide implementations for all interface methods.

Using Interface References

You can use an interface as a reference type, which allows you to work with different classes in a consistent way.

The method that runs depends on the actual object type.

Multiple Interfaces

A class in C# can implement multiple interfaces.

This allows a class to have multiple behaviors, which is not possible with inheritance alone.

Interface vs Class

Interfaces and classes are both used in object-oriented programming, but they serve different purposes.

• Class: contains both data and implementation
• Interface: defines required behavior
• Class: can only inherit one class
• Interface: can implement multiple interfaces

Real-World Example

Interfaces are commonly used to define shared behavior across different types.

Why Interfaces Matter

Interfaces are widely used in C# applications, especially in large systems and frameworks.

• Used in dependency injection
• Essential in ASP.NET applications
• Encourages loosely coupled code

Practice

Create an interface IVehicle with a Start() method. Then create Car and Bike classes that implement it.

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