using System;

​

​

// Here is an interface

public abstract class AbstractAnimal

{

    // This method/function is abstract, so the classes that subclass will 

    // need to have a getSound

    public abstract String getSound();

    // Notice that this method/function uses getSound even though it doesn't have a body.

    // Since getSound is abstract, we know that subclasses are required to have a body for it.

    // This might be a complicated method/function that we don't want to repeat in both classes.

    public void makeSound() {

        String sound = getSound();

        Console.WriteLine(sound);

    }

};

​

​

// This is a class Cow, that subclasses the Abstract class AbstractAnimal

public class Cow : AbstractAnimal { 

    // Since this class is subclass the abstract class AbstractAnimal, it has to have a body for getSound.

    // And it needs to have the override.

    public override String getSound() {

        return "moo";

    }

}

​

// Dog is similar to Cow

public class Dog : AbstractAnimal {

    public override String getSound() {

        return "roof";

    }

};

​

​

// This is the main class/program that will execute.

public class Program

{

    // Here is a function that accepts an IAnimal, and has it make a sound.

    // It doesn't care what type of animal is implemented. The parameter passed

    // will actually be a class that implements the interface IAnimal, so it

    // is guaranteed to have a method makeSound.

    public static void makeTheSound(AbstractAnimal animal) {

        animal.makeSound();

    }

    public static void Main()

    {   

        // Create a Cow and a Dog.

        Cow aCow = new Cow();

        Dog aDog = new Dog();

        // The method/function makeTheSound takes an IAnimal as its parameter.

        // Everything works as expected. This is a type of polymorphism. We could

        // do something similar with a super class instead of an interface, but if

        // IAnimal was a class, we'd have to have a body for the function makeSound.

        makeTheSound(aCow); 

        makeTheSound(aDog);

    }

}