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1、1Chapter9ObjectsandClasses2MotivationsAfterlearningtheprecedingchapters,youarecapableofsolvingmanyprogrammingproblemsusingselections,loops,methods,andarrays.However,theseJavafeaturesarenotsufficientfordevelopinggraphicaluserinterfacesandlargescalesoftwaresystems
2、.Supposeyouwanttodevelopagraphicaluserinterfaceasshownbelow.Howdoyouprogramit?3ObjectivesTodescribeobjectsandclasses,anduseclassestomodelobjects(§9.2).TouseUMLgraphicalnotationtodescribeclassesandobjects(§9.2).Todemonstratehowtodefineclassesandcreateobjects(§9.3
3、).Tocreateobjectsusingconstructors(§9.4).Toaccessobjectsviaobjectreferencevariables(§9.5).Todefineareferencevariableusingareferencetype(§9.5.1).Toaccessanobject’sdataandmethodsusingtheobjectmemberaccessoperator(.)(§9.5.2).Todefinedatafieldsofreferencetypesandass
4、igndefaultvaluesforanobject’sdatafields(§9.5.3).Todistinguishbetweenobjectreferencevariablesandprimitivedatatypevariables(§9.5.4).TousetheJavalibraryclassesDate,Random,andPoint2D(§9.6).Todistinguishbetweeninstanceandstaticvariablesandmethods(§9.7).Todefineprivat
5、edatafieldswithappropriategetandsetmethods(§9.8).Toencapsulatedatafieldstomakeclasseseasytomaintain(§9.9).Todevelopmethodswithobjectargumentsanddifferentiatebetweenprimitive-typeargumentsandobject-typearguments(§9.10).Tostoreandprocessobjectsinarrays(§9.11).Tocr
6、eateimmutableobjectsfromimmutableclassestoprotectthecontentsofobjects(§9.12).Todeterminethescopeofvariablesinthecontextofaclass(§9.13).Tousethekeywordthistorefertothecallingobjectitself(§9.14).4OOProgrammingConceptsObject-orientedprogramming(OOP)involvesprogramm
7、ingusingobjects.Anobjectrepresentsanentityintherealworldthatcanbedistinctlyidentified.Forexample,astudent,adesk,acircle,abutton,andevenaloancanallbeviewedasobjects.Anobjecthasauniqueidentity,state,andbehaviors.Thestateofanobjectconsistsofasetofdatafields(alsokno
8、wnasproperties)withtheircurrentvalues.Thebehaviorofanobjectisdefinedbyasetofmethods.5ObjectsAnobjecthasbothastateandbehavior.Thestatedefinestheobject,andthebehaviorde
