Recap: Mediator Pattern

Mediator replaces direct references between many objects with one coordinator they all report to.

• Intent. Encapsulate how a set of objects interact, so they do not refer to each other.
• Structure. Colleagues hold the mediator interface; the concrete mediator holds every colleague and their rules.
• The count. n colleagues need n(n-1)/2 links directly, and n through a mediator: 10 against 5 for five.
• Against Facade. A facade is called from outside; a mediator is called by the objects it coordinates.
• Against Observer. An observer listens to one subject; a mediator sits between colleagues that both send and receive.
• The trap. One mediator collecting every rule; keep each to one conversation.
• When not. Two or three objects, or a one-way announcement Observer already covers.