Interface Example

Here's a basic example for you.

public enum Language
{
English, German, Spanish
}

public class SpeakerFactory
{
public static ISpeaker CreateSpeaker(Language language)
{
switch (language)
{
case Language.English:
return new EnglishSpeaker();
case Language.German:
return new GermanSpeaker();
case Language.Spanish:
return new SpanishSpeaker();
default:
throw new ApplicationException("No speaker can speak such language");
}
}
}

[STAThread]
static void Main()
{
//This is your client code.
ISpeaker speaker = SpeakerFactory.CreateSpeaker(Language.English);
speaker.Speak();
Console.ReadLine();
}

public interface ISpeaker
{
void Speak();
}

public class EnglishSpeaker : ISpeaker
{
public EnglishSpeaker() { }

#region ISpeaker Members

public void Speak()
{
Console.WriteLine("I speak English.");
}

#endregion
}

public class GermanSpeaker : ISpeaker
{
public GermanSpeaker() { }

#region ISpeaker Members

public void Speak()
{
Console.WriteLine("I speak German.");
}

#endregion
}

public class SpanishSpeaker : ISpeaker
{
public SpanishSpeaker() { }

#region ISpeaker Members

public void Speak()
{
Console.WriteLine("I speak Spanish.");
}

#endregion
}