The Bridge Pattern

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The Bridge Pattern

• Guang Hu
• February 2002

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Overview

• Motivation
• Participants
• Structure
• Applicability
• Benefits
• Drawbacks
• Related Pattern

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Motivation
4
Motivation
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Motivation
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Participants

• Abstraction (Entry)
• - define the abstractions interface
• - maintains a reference to an object of type
  
• Implementor
• Refined Abstraction (Task)
• - extends the interface defined by
  Abstraction

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Participants (continue)

• Implementor (persistentImp)
• - defines an interface for implementation
• classes. Typically, this Implementors
• interface provides only primitive menthod
• ConcreteImplementor (oraclePImp, AccessPImp)
• - implements the Implementors interface

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Structure
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Applicability

• Want to avoid a permanent binding between an
  abstraction and implementation.
• When abstractions and implementations should be
  extensible through subclassing.
• When implementation changes should not impact
  clients.

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Applicability (continue)

• When the implementation should be completely
  hidden from the client. (C)
• When you have a proliferation of classes.
• When, unknown to the client, implementations are
  shared among objects.

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Benefits

• Avoid permanent binding between an abstraction
  and its implementation
• Avoid nested generalizations
• Ease adding new implementations
• Reduce code repetition
• Allow runtime switching of behaviour

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Drawbacks

• Double indirection
• - entry operation are implemented by
  subclasses of PersistentImp class. Entry class
  must delegate the message to a PersistentImp
  subclass which implements the appropriate method.
  This will have a slight impact on performance.

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Consequences

• decoupling interface implementation
• - implementation of abstraction - can be
  configured at run-time
• - eliminate compile time dependencies on
  implementation
• - encourages layering
• improved extensibility
• - Abstraction Implementer - can be extended
  independently
• hiding implementation details from clients

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Related Pattern

• Abstract Factory- The Abstract Factory pattern
  can be used by the Bridge pattern to decide which
  implementation class to instantiate for an
  abstraction object.
• Adapter

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Thank you