Csharp Interfaces And Multiple Inheritance

Task

I want to test what happens if a class inherits two or more interfaces with the same method.

I make a silly example of a class that implements Spin in two different ways. First a ballerina-interface where Spin would mean that the ballerina rotates at a certain speed. Then a cat-interface. The Swedish word for purring is Spin, so do not be confused if it makes no sense in your favourite language.

This example is available here: [1]

Inheritance Diagram

It is this simple...

 Object
  |
  +--- IBallerina
  |
  +--- ICat
  |
 myDancingKitten

IBallerina

Any ballerina can spin and answer if they need any toes cut to fit into a shoe of a certain size.

  // a dancer in a silly dress
  public interface IBallerina
  {
    void Spin(int RPM);

    bool NeedToCutToe(int ShoeSize);
  }

ICat

Cats can spin (purr in english) and answer if they need a shave.

  // Felis catus
  public interface ICat
  {
    bool NeedsShave();

    void Spin(int RPM);
  }

The class myDancingKitten

First we need a to implement the spin-, needsshave- and needtocuttoe-methods and the other functions in a small class.

  // A Felis catus in a silly dress
  public class myDancingKitten : IBallerina, ICat
  {
    public void Spin(int RPM)
    {
      Console.WriteLine("purr screeeeeeeech!!!!");
    }

    public bool NeedsShave()
    {
      //
      // shaving cats is fun, right?
      // [2]
      //
      return true;
    }

    public bool NeedToCutToe(int ShoeSize)
    {
      // all cats have very small feet
      return false; 
    }
  }

Small test class

We make a small test class with the original name program. Here we create three functions that take a ballerina, a cat and a dancing kitten and then calls its Spin function.

  static class Program
  {
    static void PlayWithBallerina(IBallerina balle)
    {
      balle.Spin(216);
    }

    static void PlayWithCat(ICat kitty)
    {
      kitty.Spin(666);
    }

    // if I ever get a kitten that can danse I'll call it Belzeebub
    static void PlayWithMyDancingKitten(myDancingKitten Belzeebub)
    {
      Belzeebub.Spin(314);
    }

    static void Main(string[] args)
    {
      myDancingKitten Belzeebub = new myDancingKitten();

      PlayWithBallerina(Belzeebub);
      PlayWithCat(Belzeebub);
      PlayWithMyDancingKitten(Belzeebub);


      Console.Write("Press Andy to continue . . . .");
      Console.ReadKey();
    }
  }

First Output

purr screeeeeeeech!!!!
purr screeeeeeeech!!!!
purr screeeeeeeech!!!!
Press Andy to continue . . . .

More advanced usage

Since it is obvious that we intend different things when we spin the cat as if it was a cat or it was a ballerina (and perhaps also as if it was a dancing kitten).

We add two more cases of the spin-method in the dancing kitten class:

    void IBallerina.Spin(int RPM)
    {
      Console.WriteLine("screeeeeeeech!!!!");
    }

    void ICat.Spin(int RPM)
    {
      Console.WriteLine("purr purr...");
    }

We now have three Spin-methods.

1. First one method that tells us how the dancing kitten will spin if it is expected to behave as a ballerina. Clearly the poor cat does not like being tossed around like that.
2. Also a method that tells us how the cat behaves if he is purring. This is nice. The cat likes to purr.
3. A final one (the first one we implemented) that tells us how the cat behaves if someone knows he is a dancing kitten and wants him to spin. This is a little strange for the cat - first he likes it then he throws up.

Advanced output

The output is different now. The testprogram is the same, but the class is different.

screeeeeeeech!!!!
purr purr...
purr screeeeeeeech!!!!
Press Andy to continue . . . .

Conclusion

This is really nice clearly a dancing kitten must be able to behave both as a cat and as a ballerina (even if he does not like it). Also a dancing kitten can behave just as a dancing kitten. This allows for nice and flexible inheritance, but still with some sort of strictness.

This page belongs in Kategori Programmering.