Structure patterns are concerned with how classes and objects are composed

ADAPTER PATTERN BY Sravanthi Karumanchi Structure Pattern Structure patterns are concerned with how classes and objects are composed to form large structures. Dierent categories Adapter Bridge Composite Decorator Façade Flyweight Proxy Scenario Outlets and Plugs Outlets in the US require a certain kind of plug. For example, a plug made in India for Indian outlet may not be used in USA. To use these appliances in USA or vice-versa we may need to purchase an adapter. Motivation Sometimes a toolkit or class library can not be used because its interface is incompatible with the interface required by an application. We can not change the library interface, since we may not have its source code. Even if we did have the source code, we probably should not change the library for each domain-speci$c application. Adapter Pattern Adapters are used to enable objects with dierent interfaces to communicate with each other. Adapter Pattern tells us how to wrap up existing classes inside a new target interface, when the need arises to reuse existing class implementations but with a dierent interface for the clients. They are also termed as wrappers. Variations in Adapters Class Adapters Use multiple inheritance to compose classes Object Adapters Object adapters use a compositional technique to adapt one interface to another. Object Pattern Client Target Request( ) Adaptee SpecificRequest( ) Adapter Request( ) Adaptee->SpecificRequest( ) adaptee Object Adapter Example Representation Application Adaptation Legacy System Financial amount() Client FinancialAdapter amount() Principal ComputeValue() Legacy Adaptee {legacyadaptee.ComputeValue();} Class Pattern Client Target Request( ) Adaptee SpecificRequest( ) Adapter Request( ) Adaptee->SpecificRequest( ) implementation Class Adapter Example Target Class class RoundPeg { public: void virtual roundPegOperation = 0; } Adaptee Class class OldSquarePeg { public: void squarePegOperation() {{ do something } } Adapter Class class PegAdapter: private OldSquarePeg, public RoundPeg { public: void virtual roundPegOperation() { add some corners; squarePegOperation(); } } Client void clientMethod() { RoundPeg* aPeg = new PegAdapter(); aPeg->roundPegOperation(); } [...]... 0; } Adaptee Class class OldSquarePeg { public: void squarePegOperation() { do something } } Adapter Class class PegAdapter: public RoundPeg { private: OldSquarePeg* square; public: PegAdapter() { square = new OldSquarePeg; } void virtual roundPegOperation() { add some corners; square>squarePegOperation(); } Collaboration Clients call operations on the Adapter instance and Adapter delegates request... only one object and no additional pointer indirection is needed to get the adaptee Object Adapter Lets a single adapter work with a group of adaptees such as a base class and all its sub classes The adapter can add functioanlity to all adaptees at once Makes it harder to override Adaptee behavior as the Adapter may not know with what Adaptee it is working with Implementation Issues How much adapting... on how similar the Target Interface is to Adapteee’s Does the adapter provide two-way transparency? A two-way adapter supports both the Target and the Adaptee interface It allows an adapted object (Adapter) to appear as an Adaptee object or a Target object Two-way Adapter A two-way adapter would also allow a RoundPeg be used in place of the SquarePeg class OldSquarePeg { public: void virtual squarePegOperation()... virtual roundPegOperation() { function } } class PegAdapter: public OldSquarePeg, RoundPeg { public: void virtual roundPegOperation() { add some corners; squarePegOperation(); } void virtual squarePegOperation() { add some corners; roundPegOperation(); } } Pluggable Adapters A class is more reusable when you minimize the assumptions other classes must make to use it.This is achieved by building interface... Adapter delegate Adaptee Adaptability Use the adapter when Want to use an existing class and its interface doesn’t match the one we need (Object Adapters only) we need to use several existing subclasses, but it’s impractical to adapt their interface by sub classing every one An object adapter can adapt the interface of its parent class Consequences Class Adapter Adapts Adaptee to Target by committing to . PATTERN BY Sravanthi Karumanchi Structure Pattern Structure patterns are concerned with how classes and objects are composed to form large structures. Dierent. Pattern Adapters are used to enable objects with dierent interfaces to communicate with each other. Adapter Pattern tells us how to wrap up existing classes