计算机专业外文文献论文翻译1Word文档格式.docx

计算机专业外文文献论文翻译1Word文档格式.docx

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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:

ThemethodbodycandeclareadditionalparametersbeyondthoserequiredfortheSingleAbstractMethodusingtheAs.Additionalannotation.TheseparameterscanhavevaluesboundtothematthepointwhereyouobtainaninstanceoftheSAMtype,andarethenpassedtothemethodeachtimeitisinvoked.

ChapmanalsosetuptheRaptprojecttoexploreotherusesofthetechnique,andhasaddedimplementationsfortwolanguagechanges-MultilineStringsandXMLliterals-thatwereconsideredforJDK7butwon'

tnowmakeitintothefinalrelease.Javacouldevengetaformofclosuressupportusingthisapproach.Whenaskedaboutthis,Chapmansaid:

WearejustfinishingaSwingprojectwhichweuseditfor.Wehavefoundacoupleofminorbugsaroundgenerictypes,onerecentlydiscoveredremainstobefixedbutotherthanthatitseemsquitenicetouse,andnobodyhasbeenwantingtorushbacktouseconventionalanonymousinnerclasses.

ProjectLombok,anotherprojectexploringthetheannotationprocessor,pushesthetechniquestillfurther.IneffectLombokusesannotationprocessingasahooktorunaJavaagentthatre-writesvariousjavacinternalsbasedontheannotations.Sinceitismanipulatinginternalclassesitisprobablynotsuitedtoproductionuse（internalclassescanchangeevenbetweenminorreleasesoftheJVM）buttheprojectisaneye-openingexampleofjustwhatcanb