Java语言程序设计10E LiangPPT习题案例13slide.ppt

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1、11Chapter13AbstractClassesandInterfaces22MotivationsYouhavelearnedhowtowritesimpleprogramstocreateanddisplayGUIcomponents.Canyouwritethecodetorespondtouseractions,suchasclickingabuttontoperformanaction?Inordertowritesuchcode,youhavetoknowaboutinterfaces.Aninterfaceisfordefiningcommon

2、behaviorforclasses(includingunrelatedclasses).Beforediscussinginterfaces,weintroduceacloselyrelatedsubject:abstractclasses.33ObjectivesTodesignanduseabstractclasses(§13.2).Togeneralizenumericwrapperclasses,BigInteger,andBigDecimalusingtheabstractNumberclass(§13.3).Toprocessacalendaru

3、singtheCalendarandGregorianCalendarclasses(§13.4).Tospecifycommonbehaviorforobjectsusinginterfaces(§13.5).Todefineinterfacesanddefineclassesthatimplementinterfaces(§13.5).TodefineanaturalorderusingtheComparableinterface(§13.6).TomakeobjectscloneableusingtheCloneableinterface(§13.7).T

4、oexplorethesimilaritiesanddifferencesamongconcreteclasses,abstractclasses,andinterfaces(§13.8).TodesigntheRationalclassforprocessingrationalnumbers(§13.9).Todesignclassesthatfollowtheclass-designguidelines(§13.10).44AbstractClassesandAbstractMethodsRunCircleRectangleTestGeometricObje

5、ctGeometricObject55abstractmethodinabstractclassAnabstractmethodcannotbecontainedinanonabstractclass.Ifasubclassofanabstractsuperclassdoesnotimplementalltheabstractmethods,thesubclassmustbedefinedabstract.Inotherwords,inanonabstractsubclassextendedfromanabstractclass,alltheabstractme

6、thodsmustbeimplemented,eveniftheyarenotusedinthesubclass.66objectcannotbecreatedfromabstractclassAnabstractclasscannotbeinstantiatedusingthenewoperator,butyoucanstilldefineitsconstructors,whichareinvokedintheconstructorsofitssubclasses.Forinstance,theconstructorsofGeometricObjectarei

7、nvokedintheCircleclassandtheRectangleclass.77abstractclasswithoutabstractmethodAclassthatcontainsabstractmethodsmustbeabstract.However,itispossibletodefineanabstractclassthatcontainsnoabstractmethods.Inthiscase,youcannotcreateinstancesoftheclassusingthenewoperator.Thisclassisusedasab

8、aseclassford