Mediator -- Design Pattern

Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Participants

    The classes and/or objects participating in this pattern are:

• Mediator (IChatroom): Defines an interface for communicating with Colleague objects
• Concrete Mediator(Chat room)

      Implements cooperative behavior by coordinating Colleague objects

      Knows and maintains its colleagues

• Colleague classes (Participant)

     Each Colleague class knows its Mediator object

     Each colleague communicates with its mediator whenever it would have otherwise communicated with another colleague

Example for Mediator Design pattern 

using System;  namespace Mediator.Structural {   /// <summary>   /// MainApp startup class for Structural   /// Mediator Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     static void Main()     {       ConcreteMediator m = new ConcreteMediator();        ConcreteColleague1 c1 = new ConcreteColleague1(m);       ConcreteColleague2 c2 = new ConcreteColleague2(m);        m.Colleague1 = c1;       m.Colleague2 = c2;        c1.Send("How are you?");       c2.Send("Fine, thanks");        // Wait for user       Console.ReadKey();     }   }    /// <summary>   /// The 'Mediator' abstract class   /// </summary>   abstract class Mediator   {     public abstract void Send(string message,       Colleague colleague);   }    /// <summary>   /// The 'ConcreteMediator' class   /// </summary>   class ConcreteMediator : Mediator   {     private ConcreteColleague1 _colleague1;     private ConcreteColleague2 _colleague2;      public ConcreteColleague1 Colleague1     {       set { _colleague1 = value; }     }      public ConcreteColleague2 Colleague2     {       set { _colleague2 = value; }     }      public override void Send(string message,       Colleague colleague)     {       if (colleague == _colleague1)       {         _colleague2.Notify(message);       }       else       {         _colleague1.Notify(message);       }     }   }    /// <summary>   /// The 'Colleague' abstract class   /// </summary>   abstract class Colleague   {     protected Mediator mediator;      // Constructor     public Colleague(Mediator mediator)     {       this.mediator = mediator;     }   }    /// <summary>   /// A 'ConcreteColleague' class   /// </summary>   class ConcreteColleague1 : Colleague   {     // Constructor     public ConcreteColleague1(Mediator mediator)       : base(mediator)     {     }      public void Send(string message)     {       mediator.Send(message, this);     }      public void Notify(string message)     {       Console.WriteLine("Colleague1 gets message: "         + message);     }   }    /// <summary>   /// A 'ConcreteColleague' class   /// </summary>   class ConcreteColleague2 : Colleague   {     // Constructor     public ConcreteColleague2(Mediator mediator) : base(mediator)     {    }      public void Send(string message)     {       mediator.Send(message, this);     }      public void Notify(string message)     {       Console.WriteLine("Colleague2 gets message: "         + message);     }   } }

Output: Colleague2 gets message: How are you? Colleague1 gets message: Fine, thanks