software Structural design pattern Adapter
- 1. Adapter-1 © Gunnar Gotshalks Adapter Pattern – Structural • Intent » Convert the interface of a class into another interface that the client expects. » Lets classes work together that couldn't otherwise
- 2. Adapter-2 © Gunnar Gotshalks Class Adapter –!Motivation • EDITOR expects a SHAPE • TEXT_VIEW is not a SHAPE • TEXT_SHAPE is a SHAPE Reuse TEXT_VIEW in the context of a SHAPE TEXT_VIEW SHAPE TEXT_SHAPE FIGURE_SHAPE EDITOR
- 3. Adapter-3 © Gunnar Gotshalks Object Adapter –!Motivation • EDITOR expects a SHAPE • TEXT_VIEW is not a SHAPE • TEXT_SHAPE is a SHAPE Reuse subclasses of TEXT_VIEW in the context of a SHAPE SHAPE TEXT_SHAPE FIGURE_SHAPE EDITOR TEXT_VIEW TEXT_A TEXT_B
- 4. Adapter-4 © Gunnar Gotshalks Adapter – Applicability • Use an existing class when its interface does not match the one you need • Create a class that cooperates with unrelated or unforeseen classes with incompatible interfaces • Object Adapter Only Need to use several existing subclasses, but it is impractical to adapt by sub-classing each one of them Object adapter adapts the interface of the parent class
- 5. Adapter-5 © Gunnar Gotshalks Adapter – Participants • TARGET Application interface • Client Target user • Adaptee Interface that needs adapting • Adapter – alternative name wrapper Provides functionality not provided by the adaptee ADAPTER ADAPTEE TARGET CLIENT Either relationship (only 1 of them for an ADAPTER) is_a – class adapter has_a – object adapter
- 6. Adapter-6 © Gunnar Gotshalks Object Adapter – Scenario ADAPTER ADAPTEE TARGET CLIENT adaptee : ADAPTEE method_in_target Scenario – collaboration 1 Client does target.method_in_target 2 Adapter does adaptee.method_in_adaptee (note polymorphism) CLIENT TARGET ADAPTEE 1 2
- 7. Adapter-7 © Gunnar Gotshalks Adapter Object – Pseudocode class ADAPTER feature adaptee : ADAPTEE ... method_in_target is pre_actions adaptee . method_in_adaptee post_actions end end end class ADAPTEE feature method_in_adaptee is ... end end end
- 8. Adapter-8 © Gunnar Gotshalks Adapter Object –!Stack Implementation • The Adapter pattern used where stack operations are calls to "equivalent" sequence operations Sequence container; • Push – Uses the Sequence putHead public void push(final Object obj) { container.putHead(obj); } • Pop –!Use the Sequence takeHead public Object pop() { return container.takeHead(); }
- 9. Adapter-9 © Gunnar Gotshalks Adapter – Consequences • There are tradeoffs –!a class adapter – inheritance » adapts Adaptee to Target by committing to concrete Adapter class Class adapter is not useful when we want to adapt a class and all its subclasses » Lets Adapter override some of Adaptee's behaviour Adapter is a subclass of Adaptee » Introduces only one object No additional pointer indirection is needed to get to adaptee
- 10. Adapter-10 © Gunnar Gotshalks Adapter – Consequences – 2 • There are tradeoffs – an object adapter – uses » One Adapter can work with many Adaptees > Adaptee and all its subclasses > Can add functionality to all Adaptees at once » Makes it harder to override Adaptee behaviour Requires making ADAPTER refer to the subclass rather than the ADAPTEE itself Or Subclassing ADAPTER for each ADAPTEE subclass
- 11. Adapter-11 © Gunnar Gotshalks Adapter – Related Patterns • Bridge is similar to object Adapter but Bridge is meant to separate interface from implementation so they can vary independently, while Adapter extends the interface of an existing object • Decorator is more transparent than Adapter, so Decorator supports recursive composition, while Adapter doesn't • Proxy defines a representative for another object and does not change its interface