The Mediator pattern promotes loose coupling by defining an object that encapsulates interactions between other objects. It defines an intermediary object that decouples classes that might otherwise be tightly coupled. The Mediator pattern allows for many-to-many relationships between interacting peers to be promoted to full object status. A mediator design example shows how a mediator class can be used to send messages between worker objects without tight coupling.

1. Mediator Pattern

2. Motivations
• lots of classes in the design of framework
• If certain principles are not applied the final
framework will end in a total mess
• to avoid tight coupled frameworks, we need a
mechanism to facilitate the interaction
between objects in a manner in that objects
are not aware of the existence of other
objects.

3. Mediator
Mediator promotes loose coupling by keeping
objects from referring to each other explicitly

4. Intent
• Define an object that encapsulates how a set
of objects interact.
• Design an intermediary to decouple
many peers
• Promote the many-to-many relationships
between interacting peers to “full
object status”.

7. Check list
• Identify a collection of interacting objects that
would benefit from mutual decoupling.
• Encapsulate those interactions in the
abstraction of a new class.
• Create an instance of that new class and
rework all “peer” objects to interact with the
Mediator only.

8. • Balance the principle of decoupling with the
principle of distributing responsibility evenly.
• Be careful not to create a “controller” or
“god” object.

9. Mediator design example
• Let us consider design of a class in which one
object send messages to other objects by
means of if then if condition explicitly

10. public class WorkerObject
{
private string _message;
public WorkerObject(string message)
{
_message = message;
}
public string Message
{
get{return _message;}
set{_message = value;
}
public SendMessage(string message)
{
Console.WriteLine(quot;Message sent : quot; + message);
}
}

11. WorkerObject senderObject = new WorkerObject(quot;message0quot;);
WorkerObject workerObject1 = new WorkerObject(quot;message1quot;);
WorkerObject workerObject2 = new WorkerObject(quot;message2quot;);
WorkerObject workerObject3 = new WorkerObject(quot;message3quot;);
if(!workerObject1.Message.Equals(senderObject.Message)
{
workerObject1.SendMessage(senderObject.Message);
}
if(!workerObject2.Message.Equals(senderObject.Message)
{
workerObject2.SendMessage(senderObject.Message);
}
if(!workerObject3.Message.Equals(senderObject.Message)
{
workerObject3.SendMessage(senderObject.Message);
}

12. Mediator
• we create a mediator class,
DoSomeMediation.
• This class contains two methods Register and
SendMessage
• The Register method catalogs all the classes
we want to mediate between.
• The SendMessage method is where the
functional code actually exists

13. public class DoSomeMediation
{
private static ArrayList _workerObjects = new ArrayList();
public static int Register(WorkerObject workerObject)
{
return _workerObjects.Add(workerObject);
}
public static void SendMessage(WorkerObject senderObject)
{
if(senderObject == null) return;
string messageToSend = senderObject.Message;
foreach(WorkerObject workerObject in _workerObjects)
{
//send message to all other objects registered
if(!workerObject.Message.Equals(senderObject.Message))
workerObject.SendMessage(messageToSend);
}
}
}

14. WorkerObject senderObject = new WorkerObject(quot;message0quot;);
WorkerObject workerObject1 = new WorkerObject(quot;message1quot;);
WorkerObject workerObject2 = new WorkerObject(quot;message2quot;);
WorkerObject workerObject3 = new WorkerObject(quot;message3quot;);
DoSomeMediation.Register(senderObject);
DoSomeMediation.Register(workerObject1);
DoSomeMediation.Register(workerObject2);
DoSomeMediation.Register(workerObject3);
DoSomeMediation.SendMessage(senderObject);

15. Flow diagram
WorkerObj1
SenderObj
Worker
Obj2

16. CCS Model
• SenderObject(reg,sendmedmsg,sendobjmsg,printmsg)=
reg.sendmedmsg’.SenderObject<reg,sendmedmsg,sendobjmsg,printmsg>
• Mediator(sendmedmsg,sendobj1msg,sendobj2msg)=
sendmedmsg.sendobj1’msg.Mediator<sendmedmsg,sendobj1msg,sendob
j2msg> +
sendmedmsg.sendobj2msg.Mediator<sendmedmsg,sendobj1msg,sendobj
2msg>
• Workerobj1(reg,sendmedmsg,sendobjmsg,printmsg)=sendobjmsg.printms
g’.Workerobj1<reg,sendmedmsg,sendobjmsg,printmsg>
• Workerobj2(reg,sendmedmsg,sendobjmsg,printmsg)=sendobjmsg.printms
g’.Workerobj2<reg,sendmedmsg,sendobjmsg,printmsg>

17. Simulation on MWB