Mediator

Origin:

GoF 95

Reason:

To coordinate the change of state of several objects.

Synopsis:

Place the logic to change the state of all the objects in a separate object, the Mediator.

Example:

A dialog box receives information to plan and reserve a banquet. Several objects contribute to this process. Changing the state of one object affects the state of other objects.

Solution:

Colleagues	A set of heterogeneous classes whose states affect each other behaviors.
EventListeners	Classes that make Colleagues unaware of the Mediator. A Colleague tells its EventListener of a change of state; the EventListener tells the Mediator.
Mediator	Class that implements the logic to execute when a Colleague changes state.