COMP2511 Decorator Pattern Adapter Pattern

COMP2511

DecoratorPatternAdapterPattern

PreparedbyDr.Ashesh Mahidadia

DesignPatterns

vCreationalPatternsv AbstractFactoryv FactoryMethodv Singleton

vStructuralPatternsv Adapterv Compositev Decorator

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vBehavioralPatternsv Iteratorv Observerv Statev Strategyv Templatev Visitor

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Weplantodiscusstherestofthedesignpatternsaboveinthefollowingweeks

DecoratorPattern

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DecoratorPattern:Intent

• "Attach additionalresponsibilities toanobjectdynamically.Decoratorsprovideaflexiblealternativetosub-classingforextendingfunctionality."[GoF]

• Decoratordesignpatternsallowustoselectivelyaddfunctionalitytoanobject(nottheclass)atruntime,basedontherequirements.

• Originalclassisnot changed(Open-ClosedPrinciple).• Inheritance extendsbehaviorsatcompiletime,additionalfunctionalityisboundtoalltheinstancesofthatclassfortheirlifetime.

• Thedecorator designpatternprefersacomposition overaninheritance.Itsastructuralpattern,whichprovidesawrapper totheexistingclass.

• Objectscanbedecorated multipletimes,indifferentorder,duetotherecursion involvedwiththisdesignpattern.SeetheexampleintheDemo.

• Donotneedtoimplementallpossiblefunctionalityinasingle(complex)class.

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DecoratorPattern:Structurev Client :referstotheComponentinterface.v Component:definesacommoninterfacefor

Component1 andDecorator objectsv Component1 :definesobjectsthatget

decorated.v Decorator:maintainsareferencetoa

Component object,andforwardsrequeststothiscomponentobject(component.operation())

v Decorator1,Decorator2,... :Implementadditionalfunctionality(addBehavior())tobeperformedbeforeand/orafterforwardingarequest.

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SeetheexampleintheDemo.

DecoratorPattern:Structurev Giventhatthedecoratorhasthesame

supertype astheobjectitdecorates,

wecanpassaroundadecorated objectinplaceoftheoriginal (wrapped)object.

v Thedecorator addsitsownbehavioreitherbeforeand/orafterdelegatingtotheobjectitdecoratestodotherestofthejob.

Fromthebook“HeadFirstDesignPattern”.

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SeetheexampleintheDemo.

DecoratorPattern:Example

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Eachcostmethodcomputesthecostofthecoffeealongwiththeothercondimentsintheorder

DecoratorPattern:Example

DecoratorPattern:Example

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DecoratorPattern:Example

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DecoratorPattern:ExampleConstructingadrinkorderwithDecorators

DecoratorPattern:Code

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DecoratorPattern:JavaI/OExample

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DecoratorPattern:JavaI/OExample

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DecoratorPattern:Code

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DecoratorPattern:

• Demo…

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AdapterPattern

16COMP2511: Decorator and Adapter Patterns

AdapterPattern:Intent

v "Converttheinterfaceofaclassintoanotherinterfaceclientsexpect.Adapterletsclassesworktogetherthatcouldn'totherwisebecauseofincompatibleinterfaces."[GoF]

v Theadapterpatternallowstheinterface ofanexistingclasstobeusedasanotherinterface,suitablefora clientclass.

v Theadapterpatternisoftenusedtomakeexistingclasses(APIs)workwith aclient classwithoutmodifyingtheirsourcecode.

v Theadapterclassmaps/joinsfunctionalityoftwodifferenttypes/interfaces.

v Theadapterpatteroffersawrapperaroundanexistingusefulclass,suchthataclientclasscanusefunctionalityoftheexistingclass.

v Theadapterpatterndonotofferadditionalfunctionality.

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AdapterPattern:Structure

v Theadaptercontainsaninstanceoftheclassitwraps.v Inthissituation,theadaptermakescallstotheinstanceofthewrappedobject.

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Adapter:Example

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Adapter:Example

DesignPatterns:DiscussDifferences

vCreationalPatternsv AbstractFactoryv FactoryMethodv Singleton

vStructuralPatternsv Adapterv Compositev Decorator

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vBehavioralPatternsv Iteratorv Observerv Statev Strategyv Templatev Visitor

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