Question

I’ve always been a little wary about polymorphism and still don’t think I understand the concept to the fullest.

I understand polymorphism as an object can take many forms. So an object can be one form then be another?

Mammal (base class)
cat (subclass of mammal) 
supercat (subclass of cat)

Cat newCat = new Cat();

Now I want the cat to be a supercat, is this “Polymorphism”?

SuperCat supCat = (SuperCat)newCat;

Isn’t this just like casting? When do you want to use casting? Is the above line of code valid? So newCat gets transformed to Supercat, does it give newCat more memory allocation? Then copies it into supCat?

NOTE — Polymorphism is the use of interfaces?

Answer 1

Just a comment on your note.

There are two types of polymorphism.

Compile time polymorphism:

This is where your polymorphic behavior is defined prior to compilation.
This happens with method overloading e.g.

public bool DoSomeThing(int myVal)
{
  // some code here
} 

public bool DoSomeThing(double myVal)
{
  // some code here
} 

Runtime polymorphism:

This is where the polymorphic behavior happens at runtime.
An example of this would be a method that accepts a type that implements a specific interface (or common base class). This interface could be of a different type depending on the code that is executing.

e.g.

public interface IWeapon
{
   void Strike();
}

public class Knife : IWeapon
{
   public void Strike()
   {
     Console.WriteLine("Stab");
   }
}

public class Gun : IWeapon
{
   public void Strike()
   {
     Console.WriteLine("Shoot");
   }
}

public class Warrior
{
  public void Attack(IWeapon weapon)
  {
    weapon.Strike();
  }
}

Now if the Warrior is given a Gun the output from Attack would be Shoot and for a Knife it would be Stab.

I haven’t tested this code so there may be syntax errors etc., but you should be able to get the idea