adapter

Adapter

Intent

Convert the interface of a class into an interface that clients expect. Adapters let classes work together that couldnt otherwise because of incompatibel interfaces

aka Wrapper

When to Use

• You want to using an existing class and its interface does not match the one you need
• You want to create a reusable class that cooperates with unrelated or unforseen classes that dont have compatible interfaces
• (Object adapter only) you need to use several existing subclasses, but its impractical to adapt their interface by subclassing each one. An object adapter can adapt the interface of its parent class

Participants

• Target (USASocketInterface)
  • Defines the domain specific interface that the client uses
• Client (ElectricDevice)
  • Collaborates with objects conforming to the Target interface
• Adaptee (Socket)
  • Defines an existing interface that needs adapting
• Adapter
  • Adapts the interface of adaptee to the Target interface

Collaborations

• Clients call operations on an Adapter instance. In turn, the adapter calls Adaptee operations that carry out the request

Consequences

Class Adapter

• Adapts Adaptee to Target by committing to a concrete Adaptee class
  • As a consequence, a class adapter wont work when we want to adapt a class and all its subclasses
• Lets Adapter override some of Adaptees behavior, since Adapter is a subclass of Adaptee
• Introduces only one object, and no additional pointer indirection is needed to get to the adaptee

Object Adapter

• Lets a single Adapter work with many Adaptees - that is the Adaptee and all of its subclasses
• Makes it harder to override Adaptee behavior

Other Considerations

• How much adapting does the Adapter do
• Pluggable adapters
  • A class is more reusable when you minimize the addumptions other classes must make to use it
• Two way adapters are good for providing transperancy
• Parameterized adapters make things easier?

Related Patterns

• Bridge has a similar structure to an object adapter, but it has a different intent
  • It is meant to separate an interface from its implementation so that they can be varied easily and independantly
  • An adapter is meant to change the interface of an existing object
• Decorator enhances another object without changing its interface
• Proxy defines a representative or surrogate for another object and does not change its interface