C#•8mo 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#
// 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!

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();

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

IAnimal

IAnimal

IAnimal data type? What does it represents and why not use

Dog

Dog

Dog

Dog instead?

FFaker Hello, I have a question, consider the following code: ```C# // Define an inter...

mtreit•5/20/25, 8:23 PM

An interface defines a contract that the class implements.

mtreit•5/20/25, 8:24 PM

You use the the interface to allow implementing generic code in the sense that it doesn't care what the underlying type is.

mtreit•5/20/25, 8:24 PM

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.

mtreit•5/20/25, 8:25 PM

That underlying type in your code example is Dog.

mtreit•5/20/25, 8:26 PM

Where it matters is when you hand it off to other code, as in my example.

Mmtreit You use the the interface to allow implementing generic code in the sense that i...

FakerOP•5/20/25, 8:26 PM

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

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

Keswiik•5/20/25, 8:26 PM

if they don't provide a default implementation, yes

Pobiega•5/20/25, 8:26 PM

you must implement all methods on an interface

Mmtreit That underlying type in your code example is Dog.

FakerOP•5/20/25, 8:26 PM

Hmm here under the hood, we are referencing a dog in memory, but what does the IAnimal mean?

FakerOP•5/20/25, 8:27 PM

yeah I see, like if they don't have a body, then we should implement them ?

mtreit•5/20/25, 8:27 PM

Yes, although you can throw NotImplementedException for methods you do not support (although best to support everything if possible.)

FFaker Hmm here under the hood, we are referencing a dog in memory, but what does the I...

mtreit•5/20/25, 8:27 PM

It just means the variable is of type IAnimal.

mtreit•5/20/25, 8:27 PM

You could later assign a different type of animal to that variable.

mtreit•5/20/25, 8:27 PM

If the variable was of type Dog you couldn't assign a Cat to it.

FakerOP•5/20/25, 8:28 PM

oh ok

mtreit•5/20/25, 8:28 PM

A variable of type IAnimal can accept either.

FakerOP•5/20/25, 8:28 PM

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

mtreit•5/20/25, 8:28 PM

Exactly.

Keswiik•5/20/25, 8:28 PM

might be beneficial to read up on polymorphism and inheritance

KKeswiik might be beneficial to read up on polymorphism and inheritance

FakerOP•5/20/25, 8:28 PM

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

Jdizzle•5/20/25, 8:29 PM

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

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

mtreit•5/20/25, 8:30 PM

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

Keswiik•5/20/25, 8:30 PM

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

Jdizzle•5/20/25, 8:31 PM

It was a question forgot ???

mtreit•5/20/25, 8:31 PM

Interface is not the same as a base class.

Jdizzle•5/20/25, 8:31 PM

That’s for abstract right ?

Keswiik•5/20/25, 8:31 PM

doesn't have to be abstract

Jdizzle•5/20/25, 8:32 PM

Private constructor ?

Keswiik•5/20/25, 8:33 PM

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•5/20/25, 8:33 PM

Oh ok .

✅ Interface in C#

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