Define an object that encapsulates how a set of objects interact.

Transcription

1 MEDIATOR Presented By: Mallampati Bhava Chaitanya Intent 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.

2 Problem Description Set of objects communicate in well-defined but complex ways. Reusing an object is difficult because it refers to and communicates with many other objects. A behavior that is distributed between several classes should be easily customizable. Structure

3 Example Example (Contd..)

4 Example (Contd..) Example (Contd..)

5 More Detailed Structure Features/Advantages Limits subclassing. Decouples colleagues. The amount of interdependence complexity involved with connecting many objects to many others decreases Simplifies object protocols. Abstracts how objects cooperate. Centralizes control. With centralized flow of information, following established constraints, There is less chance of miscommunication between objects.

6 Disadvantages Overloading the Mediator There is the potential for numerous subclasses of the Mediator and these in turn could require subclasses of those Mediator subclasses. It's just a horrible cycle from this point on. Hindrance If there are a relatively small group of objects, it may waste less time if they are able to speak to each other directly rather than through a Mediator. Implementation Issues Omitting Abstract Mediator class If colleagues work with only one Mediator Colleague-Mediator Communication Colleagues communicate Mediator when an event of interest occurs

7 Sample Code : Mediator using System; using System.Collections; abstract class Mediator // Methods abstract public void Send( string message,colleague colleague); ConcreteMediator class ConcreteMediator : Mediator // Fields private ConcreteColleague1 colleague1; private ConcreteColleague2 colleague2; // Properties public ConcreteColleague1 Colleague1 set colleague1 = value; public ConcreteColleague2 Colleague2 set colleague2 = value; // Methods override public void Send( string message,colleague colleague ) if( colleague == colleague1 ) colleague2.notify( message ); else colleague1.notify( message );

8 Colleague abstract class Colleague // Fields protected Mediator mediator; // Constructors public Colleague( Mediator mediator ) this.mediator = mediator; ConcreteColleague1 class ConcreteColleague1 : Colleague // "Constructors" public ConcreteColleague1( Mediator mediator ) : base ( mediator ) // Methods public void Send( string message ) mediator.send( message, this ); public void Notify( string message ) Console.WriteLine( "Colleague1 gets message: " + message );

9 ConcreteColleague2 class ConcreteColleague2 : Colleague // Constructors public ConcreteColleague2( Mediator mediator ) : base ( mediator ) // Methods public void Send( string message ) mediator.send( message, this ); public void Notify( string message ) Console.WriteLine( "Colleague2 gets message: " + message ); Client public class Client public static void Main(string[] args) 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" ); Output: Colleague2 gets message: How are you? Colleague1 gets message: Fine, thanks

10 Real world Examples: Relationship to Other patterns Relation to Observer: if there are no constraints on the flow, then the Mediator pattern resembles the Observer pattern. all state changes in any object are communicated by the Mediator to all other objects with no restrictions. Relation to Façade: If the only constraint on a system was to make requests but not fulfill them, then Mediator would collapse to the Façade pattern. implementation of the Mediator pattern restricted to running in a unidirectional manner rather than its general two-way messaging. Relation to Adapter: One of the key points of Mediator is that it cannot actually alter the content of the information it receives and sends, only determine its destination. if a Mediator was also allowed to change data, then it would be an Adapter object.

11 Thank you Questions?