Mediator
The Mediator is a Behavioral Design Pattern. The Mediator encapsulates how a set of objects interact with each other reducing coupling between them. The primary object of a mediator is to streamline the communication between multiple objects.
- We have complex interactions between objects.
- Mediator: Defines the interface for interacting with the colleague objects
- ConcreteMediator: If the mediator is abstract/interface, in this class we would have the references of the concrete colleague objects. If a colleague change, the mediator will notify all the others about that change.
- Colleague: Knows about the mediator and communicates with it.
- The mediators define a generic method which is called by other objects.
- This method needs to know which object has changed and optionally the property which has changed.
- This method will also notify all the others about the state change.
- You can achieve this by having the object register into the mediation or by having the mediator create these objects.
- The mediator should identify which object has sent the change notification to filter out that object in the notifications.
- Notifications must be fast or they can compromise system performance.
- If the mediator handles all routing between objects, it can become a complicated part of the code.
- We can use the observer pattern to implement the notification mechanism used to notify the mediator.
- The intent is to encapsulate complex interaction between objects.
- Specific to the objects being mediated
- The intent is to define a one-to-many relationship between objects.
- Pattern is fairly generic and it can be used with any class.
- Can get out of hand as complexity increases.
- javax.swing.ButtoGroup takes care of making sure that only buttons in a group are selected. Participating Buttons notify the mediator when they are selected.