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1、1Chapter9ObjectsandClasses2MotivationsAfterlearningtheprecedingchapters,youarecapableofsolvingmanyprogrammingproblemsusingselections,loops,methods,andarrays.However,theseJavafeaturesarenotsufficientfordevelopinggraphicaluserinterfacesandlargescalesoftwaresystems.Suppo
2、seyouwanttodevelopagraphicaluserinterfaceasshownbelow.Howdoyouprogramit?3ObjectivesTodescribeobjectsandclasses,anduseclassestomodelobjects(§9.2).TouseUMLgraphicalnotationtodescribeclassesandobjects(§9.2).Todemonstratehowtodefineclassesandcreateobjects(§9.3).Tocreateob
3、jectsusingconstructors(§9.4).Toaccessobjectsviaobjectreferencevariables(§9.5).Todefineareferencevariableusingareferencetype(§9.5.1).Toaccessanobject’sdataandmethodsusingtheobjectmemberaccessoperator(.)(§9.5.2).Todefinedatafieldsofreferencetypesandassigndefaultvaluesfo
4、ranobject’sdatafields(§9.5.3).Todistinguishbetweenobjectreferencevariablesandprimitivedatatypevariables(§9.5.4).TousetheJavalibraryclassesDate,Random,andPoint2D(§9.6).Todistinguishbetweeninstanceandstaticvariablesandmethods(§9.7).Todefineprivatedatafieldswithappropria
5、tegetandsetmethods(§9.8).Toencapsulatedatafieldstomakeclasseseasytomaintain(§9.9).Todevelopmethodswithobjectargumentsanddifferentiatebetweenprimitive-typeargumentsandobject-typearguments(§9.10).Tostoreandprocessobjectsinarrays(§9.11).Tocreateimmutableobjectsfromimmuta
6、bleclassestoprotectthecontentsofobjects(§9.12).Todeterminethescopeofvariablesinthecontextofaclass(§9.13).Tousethekeywordthistorefertothecallingobjectitself(§9.14).4OOProgrammingConceptsObject-orientedprogramming(OOP)involvesprogrammingusingobjects.Anobjectrepresentsan
7、entityintherealworldthatcanbedistinctlyidentified.Forexample,astudent,adesk,acircle,abutton,andevenaloancanallbeviewedasobjects.Anobjecthasauniqueidentity,state,andbehaviors.Thestateofanobjectconsistsofasetofdatafields(alsoknownasproperties)withtheircurrentvalues.Theb
8、ehaviorofanobjectisdefinedbyasetofmethods.5ObjectsAnobjecthasbothastateandbehavior.Thestatedefinestheobject,andthebehaviorde
