mediator

Mediator Pattern

The Mediator Pattern defines 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.

Structure

Find below the formal structure definition for the mediator pattern:

classDiagram

class Mediator
class ConcreteMediator
class Collegue
class ConcreteCollegue1
class ConcreteCollegue2

Mediator <|-- ConcreteMediator : implements
Mediator <-- Collegue : interacts-with
Collegue <|-- ConcreteCollegue1 : implements
Collegue <|-- ConcreteCollegue2 : implements
ConcreteCollegue1 --> ConcreteMediator : interacts-with
ConcreteCollegue2 --> ConcreteMediator : interacts-with

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The Mediator acts as a central point of contact between colleagues, therefore allowing for each Colleague to only care about their events, not coupling colleagues with each other or even with many others. With this pattern, each colleague only talks to the Mediator object, which applies side effects appropriately on every other colleague.

Working example

The working example for this project was extracted by the brief definition for the Mediator pattern in the Leftover patterns sections of the Head-First Design Patterns book. It's a system to manage many connected house widgets, each of them with their specific needs and interactions. The mediator pattern is used in this context to handle cross-widget interaction in a seamless way. Check out HouseOfTheFuture for implementation details and further explanations on the domain.