What Is an Interface?

What Is an Interface in C#?

An interface in C# is a contract that defines a set of methods, properties, events, or indexers—without providing any implementation. A class or struct that implements an interface must provide the implementation for all its members.

Key Features of Interfaces

• Cannot contain implementation (except default interface methods in newer C# versions).
• A class can implement multiple interfaces (supports multiple inheritance).
• Defines “what” a class should do, not “how” it should do it.
• Members are public by default.

Example in C#

interface IAnimal
{
    void MakeSound();   // method without implementation
    void Sleep();       // another method
}

class Dog : IAnimal
{
    public void MakeSound()
    {
        Console.WriteLine("Bark!");
    }

    public void Sleep()
    {
        Console.WriteLine("Sleeping...");
    }
}
    

Here, IAnimal is an interface that declares two methods. The Dog class implements this interface and provides the actual method bodies.