C#•3d ago

✅ Interface in C#

Hello, I have a question, consider the following code:

C#
// Define an interface
public interface IAnimal
{
    void Speak();
}

// Implement the interface in a class
public class Dog : IAnimal
{
    public void Speak()
    {
        Console.WriteLine("Woof!");
    }
}

C#
// Define an interface
public interface IAnimal
{
    void Speak();
}

// Implement the interface in a class
public class Dog : IAnimal
{
    public void Speak()
    {
        Console.WriteLine("Woof!");
    }
}

C#
IAnimal myDog = new Dog();  
myDog.Speak();              // Output: Woof!

C#
IAnimal myDog = new Dog();  
myDog.Speak();              // Output: Woof!

My question is, an interface is just like an abstract class in the sense that we can' instantiate directly but rather should be instantiated indirectly by using a derived class from it. When we write:

C#
IAnimal myDog = new Dog();
myDog.Speak();

C#
IAnimal myDog = new Dog();
myDog.Speak();

I don't understand, we are creating a Dog object, this references a dog? What is the IAnimal data type? What does it represents and why not use Dog instead?

22 Replies

mtreit•3d ago

An interface defines a contract that the class implements. You use the the interface to allow implementing generic code in the sense that it doesn't care what the underlying type is.

public void MakeItSpeak(IAnimal animal)
{
    // code goes here
}

public void MakeItSpeak(IAnimal animal)
{
    // code goes here
}

This code can work with anything that is an IAnimal. That underlying type in your code example is Dog. Where it matters is when you hand it off to other code, as in my example.

FakerOP•3d ago

it's mandatory to overwrite methods from an interface even if we don't use them?

Keswiik•3d ago

if they don't provide a default implementation, yes

Pobiega•3d ago

you must implement all methods on an interface

FakerOP•3d ago

Hmm here under the hood, we are referencing a dog in memory, but what does the IAnimal mean? yeah I see, like if they don't have a body, then we should implement them ?

mtreit•3d ago

Yes, although you can throw NotImplementedException for methods you do not support (although best to support everything if possible.) It just means the variable is of type IAnimal. You could later assign a different type of animal to that variable. If the variable was of type Dog you couldn't assign a Cat to it.

FakerOP•3d ago

oh ok

mtreit•3d ago

A variable of type IAnimal can accept either.

FakerOP•3d ago

on a generic term, it's an animal but under the hood, more precisely it's a dog ?

mtreit•3d ago

Exactly.

Keswiik•3d ago

might be beneficial to read up on polymorphism and inheritance

FakerOP•3d ago

yep will do so, I'm currently refreshing the OOP concepts

Jdizzle•3d ago

:base(…) is always referring to the interface if you see that too

mtreit•3d ago

Keswiik•3d ago

no, it isn't, please don't add in misinformation. interfaces do not have constructors

Jdizzle•3d ago

It was a question forgot ???

mtreit•3d ago

Interface is not the same as a base class.

Jdizzle•3d ago

That’s for abstract right ?

Keswiik•3d ago

doesn't have to be abstract

Jdizzle•3d ago

Private constructor ?

Keswiik•3d ago

I would assume not because the inheriting class shouldn't have visibility, but these questions are pretty off-topic for this thread. Might want to open up your own question if that's something you need answers for

Jdizzle•3d ago

Oh ok .

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✅ Interface in C#

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