Design Patterns -- Mediator

1. The Medaitor pattern centralizes responsibility for a particular set of objects. (Singleton pattern is for the clients.) The Mediator pattern defines an object that encapsulates how a set of object interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.  see pic:

 

2.  Mediator shows up most often in GUI application development. Java Swing components apply the Mediator pattern, notifying a mediator when events occur rather than taking reaponsibility for updating other components directly.

3 . For maintaining the ralational integrity in an object model, Mediator is also usefule. When we have an object model that is not tied to a relational database( maybe not suitable), we can use mediators to sustain the relational integrity of our model. Move the  gets and sets relations between objects into mediator.

4. We can apply mediator whenever we need to define an object that encapsulates how a set of objects interact.

5. Here giving an example for implements:

5.1 public interface Mediator { }

5.2 Concrete Mediator :

public class ConcreteMediator implements Mediator {

　　 //suppose there are 2 colleagues at present
　　 private ConcreteColleague1 colleague1 = new ConcreteColleague1();
　　 private ConcreteColleague2 colleague2 = new ConcreteColleague2();

　　 ...  // here we usually do some interact work( maybe deal with some relations....

}

5.3 Colleague :

public class Colleague {
　　 private Mediator mediator;
　　 public Mediator getMediator() {
　　 　　 return mediator;
　　 }

　　 public void setMediator( Mediator mediator ) {
　　 　　 this.mediator = mediator;
　　 }
}

public class ConcreteColleague1 { }

public class ConcreteColleague2 { }