计算机专业外文文献论文翻译.docx
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计算机专业外文文献论文翻译.docx
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计算机专业外文文献论文翻译
本科毕业设计
外文文献及译文
文献、资料题目:
EvolvingJavaWithoutChanging
theLanguage
文献、资料来源:
http:
//www。
infoq。
com/articles/
evolving—java—no-lang-change
文献、资料发表(出版)日期:
院(部):
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外文文献:
EvolvingJavaWithoutChangingtheLanguage
In"TheFeelofJava”JamesGoslingstatedthat:
Javaisabluecollarlanguage。
It’snotPhDthesismaterialbutalanguageforajob。
JavafeelsveryfamiliartomanydifferentprogrammersbecauseIhadaverystrongtendencytopreferthingsthathadbeenusedalotoverthingsthatjustsoundedlikeagoodidea。
TheextraordinarysuccessofJavaoffersweighttothenotionthatthiswasasensibleapproach,andifitremainsanimportantgoalforJavatoday,thenitmakessensethatthelanguageshouldcontinuetoevolverelativelyslowly。
Inadditiontothis,thefactthatJavaisamature,widelyusedlanguagecausesitsevolutiontobefraughtwithdifficulty。
Foronething,eachfeatureaddedtothelanguagecanchangethewayitfeelsinsubtleandoftenunpredictableways,riskingalienatingdeveloperswhohavealreadyadopteditastheirlanguageofchoice.Foranother,afeaturethatmakesperfectsenseonitsownmayinteractwithotherfeaturesofthelanguageinawkwardorunexpectedways。
Worse,oncealanguagefeaturehasbeenaddeditisallbutimpossibletoremoveevenifitturnsouttobedetrimentaltothelanguageasawhole。
Tojustifyaddinganewfeature,alanguagedesignermustbehighlyconfidentthatitwillbeoflongtermbenefittothelanguageratherthanashorttermorfashionablesolutiontoaproblemthatrapidlybecomesredundant.Tomitigatetheriskalanguagedesignerwilltypicallyexperimentbycreatingaseparatelanguageorbranch,suchasthePizzalanguageusedtoexperimentwithJava’sgenerics,priortotheirimplementation.Theproblemwiththisapproachisthattheaudienceforsuchexperimentsisbothsmallandself—selecting;obviouslytheywillallbeinterestedinlanguagefeatures,andmanymaybeacademicsorresearchers。
Anideawhichplayswelltosuchanaudiencemaystillplaybadlywhenitisincorporatedintothemainlanguageandgeneralprogrammersstarttoworkwithit。
Togetasenseofthis,considertheclosuresdebatethatbecamesoheatedforJava7.Implementationsforthemainproposals(andsomeothers)havebeenavailableforsometimebutnoconsensushasemerged。
InconsequenceSundecidedthatJDK7willnotgetfullclosuressupport.ThecoreargumentcamedowntowhetherJavahadbecomeascomplexasitcouldaffordtobewhengenerics(andinparticularthewildcardsyntax)wereaddedtoJava5;andwhethertheadditionoffullsupportforclosureswasjustifiedwhenJavaalreadyhasamorelimitedformthroughanonymousinnerclasses。
Twoimportantusecasesforaddingfullclosuressupportweretosimplifyworkingwiththefork/joinAPIthatisbeingaddedtoJDK7toimprovemulti—coreprogramming,andtohelpwithresourceclean-up.JoshBloch'sARMblockproposal,whichisnowexpectedtobeinJDK7viaProjectCoin,offersanalternativesolutiontothelatterproblem.Dr.CliffClick'sresearchonascalable,non—blockingprogrammingstyleforJavaoffersanalternativeapproachtofork/jointhatmaybemoreappropriateasthenumberofprocessorcoresincreases.Ifthisweretohappen,thentheusesforclosuresinJavamayarguablybetoolimitedtojustifytheirinclusion。
Itremainsimportantthoughthataprogramminglanguagecontinuestodevelopatsomelevel.ThisarticlethereforeexaminesthreealternativetechniquesforaddingnewlanguagefeaturestoJavathatdon’trequirechangestothelanguageitself-usingacustomDomainSpecificLanguage,exploitingtheJava6annotationprocessortoaddoptionallanguagefeaturesviaalibrary,andmovingthesyntacticsugarfromthelanguagetotheIDE.Eachoffersthepotentialtoallowawideaudienceofmainstreamdeveloperstoexperimentwiththenewfeaturesoverthemediumterminanon-invasivemanner,andthebestideascanthenfilterdownforinclusioninthecorelanguage。
CustomDSLs
ThemostwidelydiscussedofthethreeistheDomain-SpecificLanguageorDSL.Thereissomedisagreementonexactlywhatthetermmeans,butforthepurposesofthisdiscussionwe'llrefertoitsimplyasalanguagethathasbeencreatedwithanarrowfocustosolveaparticularproblem,ratherthanasageneralpurposelanguagedesignedtosolveeverycomputingproblem。
AssuchwewouldexpectaDSLtobenon—Turingcompleteandforthemostpartthisisthecase。
Thereareedgecasesofcourse。
Postscript,forexample,isaTuringcompletelanguagebutalsoqualifiesasaDSLusingourdefinition。
Astheaboveexamplealsoillustrates,theideaofaDSLisnotnew。
OtherfamiliarDSLsincludeRegularExpressions,XSLT,Ant,andJSP,allofwhichrequiresomesortofcustomparsertoprocessthem.MartinFowleralsosuggeststhatfluentinterfaces/APIscanbeconsideredasecondtypeofDSL,whichhereferstoasaninternalDSL。
HisdefinitionisthataninternalDSLisdevelopeddirectlywithinthehostlanguage。
ThiswasacommonpracticeamongstbothLispandSmalltalkprogrammers,andmorerecentlytheRubycommunityhasbeenpopularisingthetechnique.
Whilstmanywell—knownDSLsarecommerciallydevelopedandmaintained,someenterprisedevelopmentteamshaveusedthetechniquetocreatealanguagethatallowsthemtorapidlyexploreaspectsoftheirproblemdomain.Itisn’thoweverascommonasitmightbe,perhapsbecauseDSLshaveafairlyintimidatingbarriertoentry.Theteamhastodesignthelanguage,buildtheparserandpossiblyothertoolstosupporttheprogrammingteam,andtraineachnewdeveloperthatjoinstheteamonhowtheDSLworks。
HeretheemergenceoftoolstospecificallysupportDSLdevelopmentcouldsignificantlychangethelandscape.IntentionalSoftware’sIntentionalDomainWorkbench,whichhasbeenindevelopmentlongerthanJavahasbeenaround,isthefirstsignificantimplementationofsuchatool.TheprojectstartedlifeatMicrosoftResearch,andDr。
CharlesSimonyi's1995paper”TheDeathofComputerLanguages,theBirthofIntentionalProgramming"describeshisvision.In2002SimonyifoundedIntentionalSoftwaretocontinueworkingonhisideasandahugelyimpressivevideodemoofthesystemisavailable。
Theproductitselfisat1。
0status,butaccessisrestrictedtoverylimitedpartners.
Othersoftwarehousesarealsoexploringtheconcepts,amongstthemJetBrains,wellrespectedfortheirIntelliJIDEAJavaIDE,whohaverecentlyreleasedthe1.0versionoftheirMetaProgrammingSystem(MPS).MPSdoesn’tuseaparser,insteadworkingwiththeAbstractSyntaxTree(AST)directly.Itprovidesatext—likeprojectionaleditorwhichallowstheprogrammertomanipulatetheAST,andisusedtowritelanguagesandprograms.Foreachnodeinthetreeatextualprojectioniscreated—astheprogrammerworkswiththeprojection,thechangeisreflectedinthenode.Thisapproachallowsyoutoextendandembedlanguagesinanycombination(oftenreferredtoaslanguagecomposing)promotinglanguagere-use。
JetBrainsareusingtheproductinternallyandhaverecentlyreleasedYouTrack,abugtrackingproductdevelopedusingthesystem。
TheJava6AnnotationProcessor
WhilstDSLsarelesscommoninmoremainstreamlanguagessuchasJavathantheyareinRuby,SmalltalkandLisp,recentdevelopmentsintheJavalanguage,inparticulartheannotationprocessorwhichwasaddedinJava6,offernewpossibilitiesfordeveloperslookingtousetheminJava.TheJPA2.0criteriaAPIthatwillshipaspartofJavaEE6,itselfaDSL,offersanexample。
Heretheannotationprocessorbuildsupametamodeltypeforeachpersistentclassintheapplication。
WhilstitwouldbeperfectlypossibleforthedevelopertohandcraftthemetamodelinJava,itwouldbebothtediousanderrorprone.Theuseoftheannotationprocessoreliminatesthatpainand,sincetheannotationprocessorisbuiltintoJava6,theapproachrequiresnospecificIDEsupport–anIDEdelegatestotheannotationprocessortriggeredbythecompiler,andthemetadatamodelisgeneratedonthefly。
Usingtheannotationprocessoritisalsopossibleforalibrarytoaddanewlanguagefeature。
BruceChapman'sprototype”noclosures"proposal,forexample,usesthetechniquetoprovideamechanismforcastingamethodtoaSingleAbstractMethod(SAM)typewhichcompilesontopofJava6.DuringourconversationChapmanpointedoutthattheSAMtypealsosupportsfreevariables,akeyaspectofaclosure:
ThemethodbodycandeclareadditionalparametersbeyondthoserequiredfortheSingleAbstractMethodusingthe@As.Additionalannotation.TheseparameterscanhavevaluesboundtothematthepointwhereyouobtainaninstanceoftheSAMtype,andarethenpassedtothemethodeachtimeitisinvoked.
ChapmanalsosetuptheRaptprojecttoexploreotherusesofthetechnique,andhasaddedimplementationsfortwolanguagechanges-MultilineStringsandXMLliterals—thatwereconsideredforJDK7butwon’tnowmakeitintothefinalrelease.Javacouldevengetaformofclosuressupportusingthisapproach。
Whenaskedaboutthis,Chapmansaid:
WearejustfinishingaSwingprojectwhichweuseditfor.Wehavefoundacoupleofminorbugsaroundgenerictypes,onerecentlydiscoveredremainstobefixedbutotherthanthatitseemsquitenicetouse,andnobodyhasbeenwantingtorushbacktouseconventionalanonymousinnerclasses.
ProjectLombok,anotherprojectexploringthetheannotationprocessor,pushesthetechniquestillfurther。
IneffectLombokusesannotationprocessingasahooktorunaJavaagentthatre-writesvariousjavacinternals
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