Using Classes and Obje

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1、3UsingClassesandObjects5THEDITIONLewis&LoftusjavaSoftwareSolutionsFoundationsofProgramDesign©2007PearsonAddison-Wesley.AllrightsreservedUsingClassesandObjectsWecancreatemoreinterestingprogramsusingpredefinedclassesandrelatedobjectsChapter3focuseson:objectcreationandobje

2、ctreferencestheStringclassanditsmethodstheJavastandardclasslibrarytheRandomandMathclassesformattingoutputenumeratedtypeswrapperclassesgraphicalcomponentsandcontainerslabelsandimages2©2007PearsonAddison-Wesley.AllrightsreservedOutlineCreatingObjectsTheStringClassPackages

3、FormattingOutputEnumeratedTypesWrapperClassesComponentsandContainersImages3©2007PearsonAddison-Wesley.AllrightsreservedCreatingObjectsAvariableholdseitheraprimitivetypeorareferencetoanobjectAclassnamecanbeusedasatypetodeclareanobjectreferencevariableStringtitle;Noobject

4、iscreatedwiththisdeclarationAnobjectreferencevariableholdstheaddressofanobjectTheobjectitselfmustbecreatedseparately4©2007PearsonAddison-Wesley.AllrightsreservedCreatingObjectsGenerally,weusethenewoperatortocreateanobjecttitle=newString("JavaSoftwareSolutions");Thiscall

5、stheStringconstructor,whichisaspecialmethodthatsetsuptheobjectCreatinganobjectiscalledinstantiationAnobjectisaninstanceofaparticularclass5©2007PearsonAddison-Wesley.AllrightsreservedInvokingMethodsWe'veseenthatonceanobjecthasbeeninstantiated,wecanusethedotoperatortoinvo

6、keitsmethodscount=title.length()Amethodmayreturnavalue,whichcanbeusedinanassignmentorexpressionAmethodinvocationcanbethoughtofasaskinganobjecttoperformaservice6©2007PearsonAddison-Wesley.AllrightsreservedReferencesNotethataprimitivevariablecontainsthevalueitself,butanob

7、jectvariablecontainstheaddressoftheobjectAnobjectreferencecanbethoughtofasapointertothelocationoftheobjectRatherthandealingwitharbitraryaddresses,weoftendepictareferencegraphically"SteveJobs"name1num1387AssignmentRevisitedTheactofassignmenttakesacopyofavalueandstoresiti

8、navariableForprimitivetypes:num138num296Before:num2=num1;num138num238After:8ReferenceAssignmentForobjectrefere