The Mediator pattern defines an object that encapsulates how a set of classes interact, promoting loose coupling by acting as an intermediary between classes that may know nothing about each other. By consolidating all interaction in a single mediator class, dependencies between reusable classes are reduced and flexibility is improved, though this increases the complexity of the mediator itself. The mediator pattern is related to both the Observer and Facade patterns which also aim to simplify interactions between classes.

1. Mediator pattern

2. Intent
● Define an object that encapsulates how a set of
objects interact.
● Design an intermediary to decouple many
peers.
● Promote the many-to-many relationships
between interacting peers

3. Problem
● dependencies between the potentially reusable
pieces demonstrates the "spaghetti code"
phenomenon.

4. Motivation
● By consolidating all interaction in a single class,
we can regain elegance and reusability.

5. UML

6. Examples

8. Pros & Cons
Pros:
● Decouples colleagues, which facilitates independent
variations of the colleague and mediator classes.
● Simplifies protocol by replacing many-to-many interaction
with one-to-one interaction
Cons:
● Reducing the complexity of Colleagues increases
the complexity of the Mediator itself.

9. Related patterns
● Observer: the Mediator class may be
implemented using an Observer
● Facade: is similar to a Mediator, but with one-
way communication from the Facade to its
subsystem classes..