A Little OOP... C# Style

[rdrake]

Polymorphism
Everybody's favourite.

code:

using System; public class Dog {         // Notice how both methods have the same name         public void MakeNoise()         {                 // No parameters?  Bark!                 Console.WriteLine("Bark!");         }         public void MakeNoise(string noise)         {                 // Otherwise make the noise specified                 Console.WriteLine("{0}!", noise);         }         static void Main()         {                 // Create a new instance of the Dog class         Dog lassieTheRetriever = new Dog();                 // Sometimes Lassie may bark, sometimes she may                 // yip, it depends on the situation.                 lassieTheRetriever.MakeNoise();                 lassieTheRetriever.MakeNoise("Yip");         } }

Output:

code:

Bark! Yip!

Inheritance
Unfortunately C# does not support multiple inheritance, just regular inheritance. Still very simple to accomplish via the use of a colon.

code:

using System; public class Dog {         // Every healthy dog can walk, right?         public void Walk(int distance)         {                 Console.WriteLine("Walked {0}m", distance);         }         public static void Main()         {                 // Create a new instance of GoldenRetriever named                 // lassie, then walk 10m                 GoldenRetriever lassie = new GoldenRetriever();                 lassie.Walk(10);         } } // Empty class we will take advantage later public class GoldenRetriever : Dog { }

Output:

code:

Walked 10m

Method Overriding
You may run into instances where you are required to override a method entirely instead of using polymorphism. Virtual methods come in very handy for this.

code:

using System; public class Dog {         // Many dogs have their own tricks         public virtual void PerformTrick()         {                 // This method will be overwritten later :-)         }         public static void Main()         {                 // Create a new instance of GoldenRetriever named lassie                 GoldenRetriever lassie = new GoldenRetriever();                 // Lassie needs to do a trick now                 lassie.PerformTrick();         } } public class GoldenRetriever : Dog {         public override void PerformTrick()         {                 Console.WriteLine("Fetch!");         } }

Output:

code:

Fetch!

Properties
Properties allow us to change certain features of an object while still controlling access, thereby allowing us to place restrictions on the way the information is accessed and changed.

code:

using System; public class Dog {         // Every dog has some properties, they just vary         // from dog to dog.         // We don't want anybody but the setters and getters         // touching our properties.  Otherwise they may touch them         // in inappropriate ways.  By using this method we restrict         // ways the values can be modified.         private int    _numberOfLegs = 4;         private string _furColour    = "Blonde";         // Notice how these "methods" contain no parameters nor         // parenthesis and their names match those of the property         // variables, only they are in Pascal Case instead.         public int NumberOfLegs         {                 get {                         // Also notice the prefix on property variables                         return _numberOfLegs;                 } set {                         // value is a special object that holds                         // the new value passed to this block.                         _numberOfLegs = value;                 }         }         public string FurColour         {                 get { return _furColour; }                 set { _furColour = value; }         }         public static void Main()         {                 // Create a new instance of GoldenRetriever named lassie                 GoldenRetriever lassie = new GoldenRetriever();                 Console.WriteLine("Lassie\'s coat is {0} in colour and she has {1} legs", lassie.FurColour, lassie.NumberOfLegs);                 // Create another GoldenRetriever object named rebelBailey                 GoldenRetriever rebelBailey = new GoldenRetriever();                 // Sadly he only has 3 legs, and a purple coat                 rebelBailey.NumberOfLegs = 3;                 rebelBailey.FurColour    = "Purple";                 // Now display Rebel Bailey's modified properties                 Console.WriteLine("Rebel Bailey\'s coat is {0} in colour and he has {1} legs.", rebelBailey.FurColour, rebelBailey.NumberOfLegs);         } } // A breed or "subclass" of Dog public class GoldenRetriever : Dog { }

Output:

code:

Lassie's coat is Blonde in colour and she has 4 legs Rebel Bailey's coat is Purple in colour and he has 3 legs.

[wtd]

Many would argue that "virtual" methods are integral to polymorphism.

[neufelni]

Could you tell me what the difference is between polymorphism and function overloading. I've been taught that your first bit of code is function overloading.

[rdrake]

Nick @ Thu Feb 01, 2007 12:27 am wrote:

Could you tell me what the difference is between polymorphism and function overloading. I've been taught that your first bit of code is function overloading.

They really are one in the same. Sadly I cannot edit my post to reflect that.