student_answers_chapter_14

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1、SuggestedanswerforExercise14.2Asimple-mindedimplementationofthestructureinFigure14.8isgivenbelow.Itisapparentfromthecodethattheabstractsupplierinterfacehasnotbeenmodifiedwhenthenewabstractsupplierinterfacewasadded,andhencethatthemoduleisclosed.publicinte

2、rfaceAbstractSupplier{publicvoidoperation();}publicinterfaceNewAbsSupplierextendsAbstractSupplier{publicvoidnewOperation();}publicclassConcreteSupplierimplementsAbstractSupplier{publicvoidoperation(){System.out.println("ConcreteSupplier::operation()calle

3、d");}}publicclassNewConcSupplierimplementsNewAbsSupplier{publicvoidoperation(){System.out.println("NewConcSupplier::operation()called");}publicvoidnewOperation(){System.out.println("NewConcSupplier::newOperation()called");}}publicclassClient{AbstractSupp

4、liersupplier;publicClient(AbstractSuppliers){supplier=s;}publicvoiddoOperation(){supplier.operation();}}publicclassNewClient{NewAbsSuppliersupplier;publicNewClient(NewAbsSuppliers){supplier=s;}publicvoiddoOperation(){supplier.operation();}publicvoiddoNew

5、Operation(){supplier.newOperation();}}SuggestedanswerforExercise14.5ObserverDocument/ViewclassObserverclassCViewclassConcreteObserverclassCMyViewObserver.Update()CView.OnDraw()classSubjectclassCDocumentclassConcreteSubjectclassCMyDocSubject.Attach()CSubj

6、ect.AddView()Subject.Detach()CSubject.RemoveView()Subject.Notify()CSubject.UpdateAllViews()Subject.SetState()CSubject.SetStateInfo()Subject.GetState()CSubject.GetStateInfo()ThistableshowsthatvirtuallyeveryfeatureofObservercanbemappedintoacorrespondingfea

7、tureofDocument/View.Therearetwosignificantdifferencesbetweenthetwopatterns.Concreteobserversholdareferencetotheirsubjects,whereasinDocument/Viewallreferencesbetweenviewsanddocumentsaremaintainedattheabstractlevel.Inpractice,thisisnotverysignificant,andit

8、canbearguedthatDocument/ViewsupportstheassociationinObserver,asitissimplyinheritedfromthebidirectionalassociationlinkingtheabstractclasses.AnotherdifferenceisthecomplexityoftheupdateoperationinDocument/View.InObserver,the`