Adapter

1
Adapter

• SENG 609.04 Design Patterns
• Winter, 2003
• Presented by Ming Zhou, Guy Davis

2
Agenda

• Intent Motivation
• Structure
• Applicability
• Consequences
• Known Uses
• Related Patterns
• References

3
What is Adapter?

• Change the interface of a class into another
  interface which is expected by the client.
• A.K.A. Wrapper

4
Motivation
5
Structure (Class)
6
Structure (Object)
7
Applicability

• Use an existing class whose interface does not
  match the requirement
• Create a reusable class though the interfaces are
  not necessary compatible with callers

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Class Adapter Pattern

• Pros
• Only 1 new object, no additional indirection
• Less code required than the object Adapter
• Can override Adaptee's behaviour as required
• Cons
• Requires sub-classing (tough for single
  inheritance)
• Less flexible than object Adapter

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Object Adapter Pattern

• Pros
• More flexible than class Adapter
• Doesn't require sub-classing to work
• Adapter works with Adaptee and all of its
  subclasses
• Cons
• Harder to override Adaptee behavior
• Requires more code to implement properly

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Pluggable Adapters

• implemented with abstract operations

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Pluggable Adapters

• implemented with delegate objects

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Two-way Adapters
class PegAdapter public SquarePeg, RoundPeg
public void virtual roundPegOperation()
add some corners
squarePegOperation() void virtual
squarePegOperation() add some
corners roundPegOperation()

• class SquarePeg
• public
• void virtual squarePegOperation() blah

class RoundPeg public void virtual
roundPegOperation() blah
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Adapting Local Classes to RMI

• Comparison
• Increases reusability of local class
• Improves performance of local class
• Doesn't use Java single parent by subclassing
  (uses composition)

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Related Patterns

• Adapter can be similar to the remote form of
  Proxy. However, Proxy doesn't change interfaces.
• Decorator enhances another object without
  changing its interface.
• Bridge similar structure to Adapter, but
  different intent. Separates interface from
  implementation.

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Conclusions

• Allows collaboration between classes with
  incompatible interfaces
• Implemented in either class-based (inheritance)
  or object-based (composition delegation) manner
• Useful pattern which promotes reuse and allows
  integration of diverse software components

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References

• Becker, Dan. Design networked applications in RMI
  using the Adapter design pattern. JavaWorld
  Magazine, May 1999. http//www.javaworld.com/javaw
  orld/jw-05-1999/jw-05-networked.html
• Buschmann et al. A System of Patterns
  Pattern-Oriented Software Architecture. John
  Wiley and Sons. Chichester. 1996
• Gamma et al. Design Patterns Elements of
  Reusable Object-Oriented Software.
  Addison-Wesley. Boston. 1995
• Nguyen, D.X. Tutorial 10 Stacks and Queues The
  Adapter Pattern. Rice University. 1999.
  http//www.owlnet.rice.edu/comp212/99-fall/tutori
  als/10/tutorial10.html
• Whitney, Roger. CS 635 Advanced Object-Oriented
  Design Programming. San Diego State University.
  2001. http//www.eli.sdsu.edu/courses/spring01/cs6
  35/notes/proxy/proxy.htmlHeading10
• Shalloway, Alan., and Trott, James R., Design
  Patterns Explained A New Perspective on
  Object-Oriented Design, Addison-Wesley, 2002.
• Rising, Linda., The Patterns Handbook
  Techniques, Strategies, and Applications,
  Cambridge university Press, 1998.

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Questions?