软件外文翻译.docx
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软件外文翻译.docx
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软件外文翻译
学校代码:
10128
学号:
201130205034
本科毕业设计外文文献翻译
(
英文题目:
Java2MicroEditionandtheWorldofJava
题目:
J2ME和Java领域
学生姓名:
李晓燕
学院:
信息工程学院
系别:
软件工程系
专业:
软件工程
班级:
软件11-4
指导教师:
王慧讲师
企业导师:
郝传政工程师
二〇一五年五月
Java2MicroEditionandtheWorldofJava
1.Introduction
Thecomputerrevolutionofthe1970sincreasedthedemandforsophisticatedcomputersoftwaretotakeadvantageoftheever-increasingcapacityofcomputerstoprocessdata.TheCprogramminglanguagebecamethelinchpinthatenabledprogrammerstobuildsoftwarethatwasjustasrobustasthecomputeritranon.
Asthe1980sapproached,programmerswerewitnessinganotherspurtintheevolutionofprogramminglanguage.ComputertechnologyadvancedbeyondthecapabilitiesoftheCprogramminglanguage.Theproblemwasn’tnew.Itoccurredpreviouslyandcausedthedemiseofgenerationsofprogramminglanguages.Theproblemwasthatprogramswerebecomingtoocomplicatedtodesign,write,andmanagetokeepupwiththecapabilitiesofcomputers.ItwasaroundthistimethatadesignconceptbasedonSimula67andSmalltalk(fromthelate1960s)movedprogrammingtothenextevolutionarystep.Thiswastheperiodwhenobject-orientedprogramming(OOP),andwithitanewprogramminglanguagecalledC++,tookprogrammersbystorm.
In1979,BjarneStroustrupofBellLaboratoriesinNewJerseyenhancedtheCprogramminglanguagetoincludeobject-orientedfeatures.HecalledthelanguageC++.(The++istheincrementaloperatorintheCprogramminglanguage.)C++istrulyanenhancementoftheCprogramminglanguage,anditbeganasapreprocessorlanguagethatwastranslatedintoCsyntaxbeforetheprogramwasprocessedbythecompiler.
Stroustrupbuiltontheconceptofaclass(takenfromSimula67andSmalltalk),fromwhichinstancesofobjectsarecreated.Aclasscontainsdatamembersandmemberfunctionsthatdefineanobject’sdataandfunctionality.Healsointroducedtheconceptofinheritance,whichenabledaclasstoinheritsomeoralldatamembersandmemberfunctionsfromoneormoreotherclasses—allofwhichcomplementstheconceptsofobject-orientedprogramming.By1988,ANSIofficialsstandardizedStroustrup’sC++specification.
2.EnterJava
JustasC++wasbecomingthelanguageofchoiceforbuildingindustrial-strengthapplications,anothergrowthspurtintheevolutionofprogramminglanguagewasbudding,fertilizedbythelatestdisruptivetechnology—theWorldWideWeb.TheInternethadbeenawell-keptsecretfordecadesbeforetheNationalScienceFoundation(whooversawtheInternet)removedbarriersthatpreventedcommercialization.Until1991whenitwasopenedtocommerce,theInternetwasthealmostexclusivedomainofgovernmentagenciesandtheacademiccommunity.Oncethebarriertocommercializationwaslifted,theWorldWideWeb—oneofseveralservicesofferedontheInternet—becameavirtualcommunitycenterwherevisitorscouldgetfreeinformationaboutpracticallyanythingandbrowsethroughthousandsofvirtualstores.
BrowserspowertheWorldWideWeb.AbrowsertranslatesASCIItextfileswritteninHTMLintoaninteractivedisplaythatcanbeinterpretedonanymachine.AslongasthebrowseriscompatiblewiththecorrectversionofHTMLandHTTPimplementation,anycomputerrunningthebrowsercanusethesameHTMLdocumentwithouthavingtomodifyitforaparticulartypeofcomputer,whichwassomethingunheardofatthetime.ProgramswritteninCorC++aremachinedependentandcannotrunonadifferentachineunlesstheprogramisrecompiled.
TheccessoftheInternetgaverenewedfocustodevelopingamachine-independentprogramminglanguage.AndthesameyeartheInternetwascommercialized,fivetechnologistsatSunMicrosystemssetouttodojustthat.JamesGosling,PatrickNaughton,ChrisWarth,EdFrank,andMikeSheridanspent18monthsdevelopingtheprogramminglanguagetheycalledOak,whichwasrenamedJavawhenthisnewlanguagemadeitsdebutin1995.Javawentthroughnumerousiterationsbetween1991and1995,duringwhichtimemanyothertechnologistsatSunmadesubstantialcontributionstothelanguage.TheseincludedBillJoy,ArthurvanHoff,JonathanPayne,FrankYelin,andTimLindholm.
AlthoughJavaiscloselyassociatedwiththeInternet,itwasdevelopedasalanguageforprogrammingsoftwarethatcouldbeembeddedintoelectronicdevicesregardlessofthetypeofCPUusedbythedevice.ThisisknownastheEmbeddedJavaplatformandisincontinuoususetodayforclosedsystems.
TheJavateamfromSunsucceededincreatingaportableprogramminglanguage,somethingthathadeludedprogrammerssincecomputerswerefirstprogrammed.Theirsuccess,however,wasfarbeyondtheirwildestdreams.ThesameconceptusedtomakeJavaprogramsportabletoelectronicdevicesalsocouldbeusedtomakeJavaprogramsrunoncomputersrunningMicrosoftWindows,UNIX,andMacintosh.Timingwasperfect.TheInternet/intranethadwhettedcorporateAmerica’sappetiteforcost-effective,portableprogramsthatcouldreplacemission-criticalapplicationswithinthecorporation.AndJavahadprovenitselfasaprogramminglanguageusedtosuccessfullydevelopmachine-independentapplications.
3.JavaVirtualMachine
WritingJavaprogramsissimilartowritingC++programsinthattheprogrammerwritessourcecodethatcontainsinstructionsintoaneditor,orinanintegrateddevelopmentenvironment,andthenthesourcecodeiscompiled.However,that’swhereJavaandC++partways.ThecompilingandlinkingprocessofaC++programresultsinanexecutablethatcanberunonanappropriatemachine.Incontrast,theJavacompilerconvertsJavasourcecodeintobytecodethatisexecutedbytheJavaVirtualMachine(JVM).
Machine-specificinstructionsarenotincludedinbytecode.Instead,theyalreadyresideintheJVM,whichismachinespecific.ThismeansthatthebytecodemightcontainfewerinstructionsthatneedtobetranslatedthanacomparableC++program.
AlthoughtheJavacompilergeneratesbytecodethatmustbeinterpretedbytheJVMatruntime,thenumberofinstructionsthatneedtranslationareusuallyminimalandhavealreadybeenoptimizedbytheJavacompiler.
4.BacktotheFuture:
J2ME
RememberthatJavabeganasaprogramminglanguagetocreateprogramsforembeddedsystems—microcomputersfoundinconsumerandindustrialproductssuchasthoseusedtocontrolautomobilesandappliances.ThedevelopmentteamatSunworkedonJavaintheearly1990stoaddresstheprogrammingneedsofthefledglingembeddedcomputermarket,butthateffortwassidetrackedbymorecompellingopportunitiespresentedbytheInternet.
Asthoseopportunitieswereaddressed,anewbreedofportablecommunicationsdevicesopenedotheropportunitiesattheturnofthecentury.CellphonesexpandedJ2ME:
TheCompleteReferencefromvoicecommunicationsdevicestovoiceandtextcommunicationsdevices.Pocketelectronictelephonedirectoriesevolvedintopersonaldigitalassistants.Chipmakerswerereleasingnewproductsatthistimethatweredesignedtotransfercomputingpowerfromadesktopcomputerintomobilesmallcomputersthatcontrolledgaspumps,cabletelevisionboxes,andanassortmentofotherappliances.
ThetimewasrightforthenextevolutionofJava.However,insteadofbeefingupJavawithadditionalAPIs,theteamatSun,alongwiththeJavaCommunityProcessProgram,dismantledboththeJavaprogramminglanguageandtheJavaVirtualMachine.TheystrippeddownJavaAPIsandtheJVMtotheminimumcodingrequiredtoprovideintelligencetoembeddedsystemsandmicrocomputerdevices.Thiswasnecessarybecauseofresourceconstraintsimposeduponthehardwaredesignofthesedevices.TheresultoftheireffortsisJ2ME.J2MEisareducedversionoftheJavaAPIandJavaVirtualMachinethatisdesignedtooperatewithinthesparseresourcesavailableinthenewbreedofembeddedcomputersandmicrocomputers.
5.HowJ2MEIsOrganized
Traditionalcomputingdevicesusefairlystandardhardwareconfigurationssuchasadisplay,keyboard,mouse,andlargeamountsofmemoryandpermanentstorage.However,thenewbreedofcomputingdeviceslackshardwareconfigurationcontinuityamongdevices.Somedevicesdon’thaveadisplay,permanentstorage,keyboard,ormouse.Andmemoryavailabilityisinconsistentamongsmallcomputingdevices.ThelackofuniformhardwareconfigurationamongthesmallcomputingdevicesposesaformidablechallengefortheJavaCommunityProcessProgram,whichischargedwithdevelopingstandardsfortheJVMandtheJ2MEforsmallcomputingdevices.
J2MEmustservicemanydifferentkindsofsmallcomputingdevices,includingscreenphones,digitalset-topboxesusedforcabletelevision,cellphones,andpersonaldigitalassistants.ThechallengefortheJavaCommunityProcessProgramistodevelopaJavastandardthatcanbeimplementedonsmallcomputingdevicesthathavenonstandardhardwareconfigurations.TheJavaCommunityProcessProgramhasusedatwofoldapproachtoaddressingtheneedsofsmallcomputingdevices.First,theydefinedtheJavarun-timeenvironmentandcoreclassesthatoperateoneachdevice.Thisisreferredtoastheconfiguration.AconfigurationdefinestheJavaVirtualMachineforaparticularsmallcomputingdevice.Therearetwoconfigurations,oneforhandhelddevicesandtheotherforplug-indevices.Next,theJavaCommunityProcessProgramdefinedaprofileforcategoriesofsmallcomputingdevices.Aprofileconsistsofclassesthatenabledeveloperstoimplementfeaturesfoundonarelatedgroupofsmallcomputingdevices.
6.J2MEconfigurations
TherearetwoconfigurationsforJ2MEasofthiswriting.TheseareConnectedLimitedDeviceConfiguration(CLDC)andtheConnectedDevice
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