java中英文对照Word下载.docx
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java中英文对照Word下载.docx
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java中英文对照@#@1.IntroductionToObjects@#@1.1Theprogressofabstraction@#@Allprogramminglanguagesprovideabstractions.Itcanbearguedthatthecomplexityoftheproblemsyou’reabletosolveisdirectlyrelatedtothekindandqualityofabstraction.By“kind”Imean,“Whatisitthatyouareabstracting?
@#@”Assemblylanguageisasmallabstractionoftheunderlyingmachine.Manyso-called“imperative”languagesthatfollowed(suchasFORTRAN,BASIC,andC)wereabstractionsofassemblylanguage.Theselanguagesarebigimprovementsoverassemblylanguage,buttheirprimaryabstractionstillrequiresyoutothinkintermsofthestructureofthecomputerratherthanthestructureoftheproblemyouaretryingtosolve.Theprogrammermustestablishtheassociationbetweenthemachinemodel(inthe“solutionspace,”whichistheplacewhereyou’remodelingthatproblem,suchasacomputer)andthemodeloftheproblemthatisactuallybeingsolved(inthe“problemspace,”whichistheplacewheretheproblemexists).Theeffortrequiredtoperformthismapping,andthefactthatitisextrinsictotheprogramminglanguage,producesprogramsthataredifficulttowriteandexpensivetomaintain,andasasideeffectcreatedtheentire“programmingmethods”industry.@#@Thealternativetomodelingthemachineistomodeltheproblemyou’retryingtosolve.EarlylanguagessuchasLISPandAPLchoseparticularviewsoftheworld(“Allproblemsareultimatelylists”or“Allproblemsarealgorithmic,”respectively).PROLOGcastsallproblemsintochainsofdecisions.Languageshavebeencreatedforconstraint-basedprogrammingandforprogrammingexclusivelybymanipulatinggraphicalsymbols.(Thelatterprovedtobetoorestrictive.)Eachoftheseapproachesisagoodsolutiontotheparticularclassofproblemthey’redesignedtosolve,butwhenyoustepoutsideofthatdomaintheybecomeawkward.@#@Theobject-orientedapproachgoesastepfurtherbyprovidingtoolsfortheprogrammertorepresentelementsintheproblemspace.Thisrepresentationisgeneralenoughthattheprogrammerisnotconstrainedtoanyparticulartypeofproblem.Werefertotheelementsintheproblemspaceandtheirrepresentationsinthesolutionspaceas“objects.”(Youwillalsoneedotherobjectsthatdon’thaveproblem-spaceanalogs.)Theideaisthattheprogramisallowedtoadaptitselftothelingooftheproblembyaddingnewtypesofobjects,sowhenyoureadthecodedescribingthesolution,you’rereadingwordsthatalsoexpresstheproblem.Thisisamoreflexibleandpowerfullanguageabstractionthanwhatwe’vehadbefore.Thus,OOPallowsyoutodescribetheproblemintermsoftheproblem,ratherthanintermsofthecomputerwherethesolutionwillrun.There’sstillaconnectionbacktothecomputer:
@#@eachobjectlooksquiteabitlikealittlecomputer—ithasastate,andithasoperationsthatyoucanaskittoperform.However,thisdoesn’tseemlikesuchabadanalogytoobjectsintherealworld—theyallhavecharacteristicsandbehaviors.@#@AlanKaysummarizedfivebasiccharacteristicsofSmalltalk,thefirstsuccessfulobject-orientedlanguageandoneofthelanguagesuponwhichJavaisbased.Thesecharacteristicsrepresentapureapproachtoobject-orientedprogramming:
@#@@#@1.Everythingisanobject.Thinkofanobjectasafancyvariable;@#@itstoresdata,butyoucan“makerequests”tothatobject,askingittoperformoperationsonitself.Intheory,youcantakeanyconceptualcomponentintheproblemyou’retryingtosolve(dogs,buildings,services,etc.)andrepresentitasanobjectinyourprogram.@#@2.Aprogramisabunchofobjectstellingeachotherwhattodobysendingmessages.Tomakearequestofanobject,you“sendamessage”tothatobject.Moreconcretely,youcanthinkofamessageasarequesttocallamethodthatbelongstoaparticularobject.@#@3.Eachobjecthasitsownmemorymadeupofotherobjects.Putanotherway,youcreateanewkindofobjectbymakingapackagecontainingexistingobjects.Thus,youcanbuildcomplexityintoaprogramwhilehidingitbehindthesimplicityofobjects.@#@4.Everyobjecthasatype.Usingtheparlance,eachobjectisaninstanceofaclass,inwhich“class”issynonymouswith“type.”Themostimportantdistinguishingcharacteristicofaclassis“Whatmessagescanyousendtoit?
@#@”@#@5.Allobjectsofaparticulartypecanreceivethesamemessages.Thisisactuallyaloadedstatement,asyouwillseelater.Becauseanobjectoftype“circle”isalsoanobjectoftype“shape,”acircleisguaranteedtoacceptshapemessages.Thismeansyoucanwritecodethattalkstoshapesandautomaticallyhandleanythingthatfitsthedescriptionofashape.ThissubstitutabilityisoneofthepowerfulconceptsinOOP.@#@Boochoffersanevenmoresuccinctdescriptionofanobject:
@#@@#@Anobjecthasstate,behaviorandidentity.@#@Thismeansthatanobjectca
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