第十二章 面向对象编程chapter12_object-oriented design

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1、PythonProgramming,3/e1PythonProgramming:AnIntroductionToComputerScienceChapter12Object-OrientedDesignPythonProgramming,3/e2Tounderstandtheprocessofobject-orienteddesign.Tobeabletoreadandunderstandobject-orientedprograms.Tounderstandtheconceptsofencapsulation,polymorphismandinheritanceasthey

2、pertaintoobject-orienteddesignandprogramming.ObjectivesPythonProgramming,3/e3ObjectivesTobeabletodesignmoderatelycomplexsoftwareusingobject-orienteddesign.PythonProgramming,3/e4TheProcessofOODMostmoderncomputerapplicationsaredesignedusingadata-centeredviewofcomputingcalledobject-orienteddesig

3、n(OOD).TheessenceofOODisdescribingasystemintermsofmagicalblackboxesandtheirinterfaces.PythonProgramming,3/e5TheProcessofOODEachcomponentprovidesaserviceorsetofservicesthroughitsinterface.Othercomponentsareusersorclientsoftheservices.Aclientonlyneedstounderstandtheinterfaceofaservice–implement

4、ationdetailsarenotimportant;theymaybechangedandshouldn’taffecttheclientatall!PythonProgramming,3/e6TheProcessofOODThecomponentprovidingtheserviceshouldn’thavetoconsiderhowtheserviceisused–itjustneedstoprovidetheservice“asadvertised”viatheinterface.Thisseparationofconcernsmakesthedesignofcompl

5、exsystemspossible.PythonProgramming,3/e7TheProcessofOODIntop-downdesign,functionsservetheroleoftheblackbox.Clientprogramscanusethefunctionsaslongasitunderstandswhatthefunctiondoes.Howthefunctionaccomplishesitstaskisencapsulatedwithinthefunction.PythonProgramming,3/e8TheProcessofOODInOOD,thebl

6、ackboxesareobjects.Themagicbehindtheobjectsisintheclassdefinitions.Onceaclassdefinitioniswritten,wecanignorehowtheclassworksandrelyontheexternalinterface,itsmethods.You’veseenthiswhenusingthegraphicslibrary–youwereabletodrawacirclewithouthavingtoknowallthenitty-grittydetailsencapsulatedinclas

7、sdefinitionsforGraphWinandCircle.PythonProgramming,3/e9TheProcessofOODBreakingalargeproblemintoasetofcooperatingclassesreducesthecomplexitythatmustbeconsideredtounderstandanygivenpartoftheprogram.Eachclassstandsonitsown!OODistheprocessoffindi