Why and when use polymorphism?

Question

I'm new to OOP and polymorphism has given me a hard time:

class Animal
{
    public virtual void eat()
    {
        Console.Write("Animal eating");
    }
}
class Dog : Animal
{
    public override void eat()
    {
        Console.Write("Dog eating");
    }
}
class Program
{
    public void Main()
    {
        Animal dog = new Dog();
        Animal generic = new Animal();
        dog.eat();
        generic.eat();
    }
}

So that prints

Dog eating
Animal eating

But why not to just use the Dog type instead of animal, like Dog dog = new Dog()? I assume this comes handy when you know the object is a animal, but don't know what kind of animal it is. Please explain this to me.

Thanks

Answer 1

You can refer to a subclass by its super class.

Animal dog = new Dog();
Animal cat = new Cat();
Animal frog = new Frog();

List<Animal> animals = new List<Animal>();

animals.add(dog);
animals.add(cat);
animals.add(frog);

foreach(Animal animal in animals)
{   
    Console.WriteLine(animal.eat());
}