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Bridge

Difficulty-Intermediate Gang Of Four Java Structural

Also known as

Handle/Body

Intent

Decouple an abstraction from its implementation so that the two can vary independently.

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Applicability

Use the Bridge pattern when

  • you want to avoid a permanent binding between an abstraction and its implementation. This might be the case, for example, when the implementation must be selected or switched at run-time.
  • both the abstractions and their implementations should be extensible by subclassing. In this case, the Bridge pattern lets you combine the different abstractions and implementations and extend them independently
  • changes in the implementation of an abstraction should have no impact on clients; that is, their code should not have to be recompiled.
  • you have a proliferation of classes. Such a class hierarchy indicates the need for splitting an object into two parts. Rumbaugh uses the term "nested generalizations" to refer to such class hierarchies
  • you want to share an implementation among multiple objects (perhaps using reference counting), and this fact should be hidden from the client. A simple example is Coplien's String class, in which multiple objects can share the same string representation.

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