Applied Design Patterns with Java

Behavioral :: Mediator (273) {C ch 20}

Applicability

Use the Mediator pattern when:

• a set of objects communicate in well-defined but complex ways. The resulting interdependencies are unstructured and difficult to understand.
• reusing an object is difficult because it refers to and communicates with many other objects.
• a behavior that's distributed between several classes should be customizable without a lot of subclassing.

Structure

A typical object structure might look like this:

Participants

• Mediator (DialogDirector) defines an interface for communicating with Colleague objects.
• ConcreteMediator (FontDialogDirector) implements cooperative behavior by coordinating Colleague objects, and knows and maintains its colleagues.
• Colleague classes (ListBox, EntryField) each Colleague class knows its Mediator object, and each colleague communicates with its mediator whenever it would have otherwise communicated with another colleague.

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