汇编语言对象入门中英文对照外文翻译文献.docx

汇编语言对象入门中英文对照外文翻译文献.docx

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汇编语言对象入门中英文对照外文翻译文献

中英文资料外文翻译文献

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.

Thismeansthatanobjectcanhaveinternaldata（whichgivesitstate）,methods（toproducebehavior）,andeachobjectcanbeuniquelydistinguishedfromeveryotherobject—toputthisinaconcretesense,eachobjecthasauniqueaddressinmemory.

1.2Anobjecthasaninterface

Aristotlewasprobablythefirsttobeginacarefulstudyoftheconceptoftype;hespokeof“theclassoffishesandtheclassofbirds.”Theideathatallobjects,whilebeingunique,arealsopartofaclassofobjectsthathavecharacteristicsandbehaviorsincommonwasuseddirectlyinthefirstobject-orientedlanguage,Simula-67,withitsfundamentalkeywordclassthatintroducesanewtypeintoaprogram.

Simula,asitsnameimplies,wascreatedfordevelopingsimulationssuchastheclassic“banktellerproblem.”Inthis,youhaveabunchoftellers,customers,accounts,transactions,andunitsofmoney—alotof“objects.”Objectsthatareidenticalexceptfortheirstateduringaprogram’sexecutionaregroupedtogetherinto“classesofobjects”andthat’swherethekeywordclasscamefrom.Creatingabstractdatatypes（classes）isafundamentalconceptinobject-orientedprogramming.Abstractdatatypesworkalmostexactlylikebuilt-intypes:

Youcancreatevariablesofatype（calledobjectsorinstancesinobject-orientedparlance）andmanipulatethosevariables（calledsendingmessagesorrequests;yousendamessageandtheobjectfiguresoutwhattodowithit）.Themembers（elements）ofeachclasssharesomecommonality:

everyaccounthasabalance,everytellercanacceptadeposit,etc.Atthesametime,eachmemberhasitsownstate:

eachaccounthasadifferentbalance,eachtellerhasaname.Thus,thetellers,customers,accounts,transactions,etc.,caneachberepresentedwithauniqueentityinthecomputerprogram.Thisentityistheobject,andeachobjectbelongstoaparticularclassthatdefinesitscharacteristicsandbehaviors.

So,althoughwhatwereallydoinobject-orientedprogrammingiscreatenewdatatypes,virtuallyallobject-orientedprogramminglanguagesusethe“class”keyword.Whenyouseetheword“type”think“class”andviceversa.

Sinceaclassdescribesasetofobjectsthathaveidenticalcharacteristics（dataelements）andbehaviors（functionality）,aclassisreallyadatatypebecauseafloatingpointnumber,forexample,alsohasasetofcharacteristicsandbehaviors.Thedifferenceisthataprogrammerdefinesaclasstofitaproblemratherthanbeingforcedtouseanexistingdatatypethatwasdesignedtorepresentaunitofstorageinamachine.Youextendtheprogramminglanguagebyaddingnewdatatypesspecifictoyourneeds.Theprogrammingsystemwelcomesthenewclassesandgivesthemallthecareandtype-checkingthatitgivestobuilt-intypes.

Theobject-orientedapproachisnotlimitedtobuildingsimulations.Whetherornotyouagreethatanyprogramisasimulationofthesystemyou’redesigning,theuseofOOPtechniquescaneasilyreducealargesetofproblemstoasimplesolution.

Onceaclassisestablished,youcanmakeasmanyobjectsofthatclassasyoulike,andthenmanipulatethoseobjectsasiftheyaretheelementsthatexistintheproblemyouaretryingtosolve.Indeed,oneofthechallengesofobject-orientedprogrammingistocreateaone-to-onemappingbetweentheelementsintheproblemspaceandobjectsinthesolutionspace.

Buthowdoyougetanobjecttodousefulworkforyou?

Theremustbeawaytomakearequestoftheobjectsothatitwilldosomething,suchascompleteatransaction,drawsomethingonthescreen,orturnonaswitch.Andeachobjectcansatisfyonlycertainrequests.Therequestsyoucanmakeofanobjectaredefinedbyitsinterface,andthetypeiswhatdeterminestheinterface.Asimpleexamplemightbearepresentationofalightbulb:

Light

On（）

Off（）

Lightlt=newLight（）;

lt.on（）;

Theinterfaceestablisheswhatrequestsyoucanmakeforaparticularobject.However,theremustbecodesomewheretosatisfythatrequest.This,alongwiththehiddendata,comprisestheimplementation.Fromaproceduralprogrammingstandpoint,it’snotthatcomplicated.Atypehasamethodassociatedwitheachpossiblerequest,andwhenyoumakeaparticularrequesttoanobject,thatmethodiscalled.Thisprocessisusuallysummarizedbysayingthatyou“sendamessage”（makearequest）toanobject,andtheobjectfiguresoutwhattodowiththatmessage（itexecutescode）.

Here,thenameofthetype/classisLight,thenameofthisparticularLightobjectislt,andtherequeststhatyoucanmakeofaLightobjectaretoturniton,turnitoff,makeitbrighter,ormakeitdimmer.YoucreateaLightobjectbydefininga“reference”（lt）forthatobjectandcallingnewtorequestanewobjectofthattype.Tosendamessagetotheobject,youstatethenameoftheobjectandconnectitto