Java外文翻译programminglanguage教程文件文档格式.docx

Java外文翻译programminglanguage教程文件文档格式.docx

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1History

1.1Principles

1.2Versions

2Practices

2.1Javaplatform

2.1.1Implementations

2.1.2Performance

2.2Automaticmemorymanagement

History

Seealso:

Java（softwareplatform）#History

JamesGosling,MikeSheridan,andPatrickNaughtoninitiatedtheJavalanguageprojectinJune1991.[12]Javawasoriginallydesignedforinteractivetelevision,butitwastooadvancedforthedigitalcabletelevisionindustryatthetime.[13]ThelanguagewasinitiallycalledOakafteranoaktreethatstoodoutsideGosling'

soffice;

itwentbythenameGreenlater,andwaslaterrenamedJava,fromJavacoffee,saidtobeconsumedinlargequantitiesbythelanguage'

screators.[14]GoslingaimedtoimplementavirtualmachineandalanguagethathadafamiliarC/C++styleofnotation.[15]

SunMicrosystemsreleasedthefirstpublicimplementationasJava1.0in1995.Itpromised"

WriteOnce,RunAnywhere"

（WORA）,providingno-costrun-timesonpopularplatforms.Fairlysecureandfeaturingconfigurablesecurity,itallowednetwork-andfile-accessrestrictions.MajorwebbrowserssoonincorporatedtheabilitytorunJavaappletswithinwebpages,andJavaquicklybecamepopular.WiththeadventofJava2（releasedinitiallyasJ2SE1.2inDecember1998–1999）,newversionshadmultipleconfigurationsbuiltfordifferenttypesofplatforms.Forexample,J2EEtargetedenterpriseapplicationsandthegreatlystripped-downversionJ2MEformobileapplications（MobileJava）.J2SEdesignatedtheStandardEdition.In2006,formarketingpurposes,SunrenamednewJ2versionsasJavaEE,JavaME,andJavaSE,respectively.

In1997,SunMicrosystemsapproachedtheISO/IECJTC1standardsbodyandlatertheEcmaInternationaltoformalizeJava,butitsoonwithdrewfromtheprocess.[16]Javaremainsadefactostandard,controlledthroughtheJavaCommunityProcess.[17]Atonetime,SunmademostofitsJavaimplementationsavailablewithoutcharge,despitetheirproprietarysoftwarestatus.SungeneratedrevenuefromJavathroughthesellingoflicensesforspecializedproductssuchastheJavaEnterpriseSystem.SundistinguishesbetweenitsSoftwareDevelopmentKit（SDK）andRuntimeEnvironment（JRE）（asubsetoftheSDK）;

theprimarydistinctioninvolvestheJRE'

slackofthecompiler,utilityprograms,andheaderfiles.

OnNovember13,2006,SunreleasedmuchofJavaasfreeandopensourcesoftware,（FOSS）,underthetermsoftheGNUGeneralPublicLicense（GPL）.OnMay8,2007,Sunfinishedtheprocess,makingallofJava'

scorecodeavailableunderfreesoftware/open-sourcedistributionterms,asidefromasmallportionofcodetowhichSundidnotholdthecopyright.[18]

Sun'

svice-presidentRichGreensaidthatSun'

sidealrolewithregardstoJavawasasan"

evangelist."

[19]FollowingOracleCorporation'

sacquisitionofSun

Microsystemsin2009–2010,Oraclehasdescribeditselfasthe"

stewardofJavatechnologywitharelentlesscommitmenttofosteringacommunityofparticipationandtransparency"

.[20]Javasoftwarerunsonlaptopstodatacenters,gameconsolestoscientificsupercomputers.Thereare930millionJavaRuntimeEnvironmentdownloadseachyearand3billionmobilephonesrunJava.[21]OnApril2,2010,JamesGoslingresignedfromOracle.[22]

Principles

TherewerefiveprimarygoalsinthecreationoftheJavalanguage:

[23]

1.Itshouldbe"

simple,object-orientedandfamiliar"

2.Itshouldbe"

robustandsecure"

3.Itshouldbe"

architecture-neutralandportable"

4.Itshouldexecutewith"

highperformance"

5.Itshouldbe"

interpreted,threaded,anddynamic"

Versions

Mainarticle:

Javaversionhistory

MajorreleaseversionsofJava,alongwiththeirreleasedates:

JDK1.0（January23,1996）

JDK1.1（February19,1997）

J2SE1.2（December8,1998）

J2SE1.3（May8,2000）

J2SE1.4（February6,2002）

J2EE5.0（September30,2004）

JavaSE6（December11,2006）

JavaSE7（July28,2011）

Practices

Javaplatform

Mainarticles:

Java（softwareplatform）andJavaVirtualMachine

OnecharacteristicofJavaisportability,whichmeansthatcomputerprogramswrittenintheJavalanguagemustrunsimilarlyonanyhardware/operating-systemplatform.ThisisachievedbycompilingtheJavalanguagecodetoanintermediaterepresentationcalledJavabytecode,insteadofdirectlytoplatform-specificmachinecode.Javabytecodeinstructionsareanalogoustomachinecode,butareintendedtobeinterpretedbyavirtualmachine（VM）writtenspecificallyforthehosthardware.End-userscommonlyuseaJavaRuntimeEnvironment（JRE）installedontheirownmachineforstandaloneJavaapplications,orinaWebbrowserforJavaapplets.

Standardizedlibrariesprovideagenericwaytoaccesshost-specificfeaturessuchasgraphics,threading,andnetworking.

Amajorbenefitofusingbytecodeisporting.However,theoverheadofinterpretationmeansthatinterpretedprogramsalmostalwaysrunmoreslowlythanprogramscompiledtonativeexecutableswould.Just-in-Timecompilerswereintroducedfromanearlystagethatcompilebytecodestomachinecodeduringruntime.

Implementations

SunMicrosystemsofficiallylicensedtheJavaStandardEditionplatformforLinux,[24]MacOSX,[25]andSolaris.InthepastSunlicensedJavatoMicrosoftbutthelicenseexpiredwithoutrenewal.[26]BecauseWindowsdoesnotshipwithaJavasoftwareplatform,anetworkofthird-partyvendorsandlicensees[27]developthemforWindowsandotheroperatingsystem/hardwareplatforms.

strademarklicenseforusageoftheJavabrandinsiststhatallimplementationsbe"

compatible"

.ThisresultedinalegaldisputewithMicrosoftafterSunclaimedthattheMicrosoftimplementationdidnotsupportRMIorJNIandhadaddedplatform-specificfeaturesoftheirown.Sunsuedin1997,andin2001wonasettlementofUS$20million,aswellasacourtorderenforcingthetermsofthelicensefromSun.[28]Asaresult,MicrosoftnolongershipsJavawithWindows,andinrecentversionsofWindows,InternetExplorercannotsupportJavaappletswithoutathird-partyplugin.Sun,andothers,havemadeavailablefreeJavarun-timesystemsforthoseandotherversionsofWindows.

Platform-independentJavaisessentialtotheJavaEEstrategy,andanevenmorerigorousvalidationisrequiredtocertifyanimplementation.Thisenvironmentenablesportableserver-sideapplications,suchasWebservices,JavaServlets,andEnterpriseJavaBeans,aswellaswithembeddedsystemsbasedonOSGi,usingEmbeddedJavaenvironments.ThroughtheGlassFishproject,Sunisworkingtocreateafullyfunctional,unifiedopensourceimplementationoftheJavaEEtechnologies.

SunalsodistributesasupersetoftheJREcalledtheJavaDevelopmentKit（commonlyknownastheJDK）,whichincludesdevelopmenttoolssuchastheJavacompiler,Javadoc,Jar,anddebugger.

Performance

Javaperformance

ProgramswritteninJavahaveareputationforbeingslowerandrequiringmorememorythanthosewritteninC.[29]However,Javaprograms'

executionspeedimprovedsignificantlywiththeintroductionofJust-in-timecompilationin1997/1998forJava1.1,[30]theadditionoflanguagefeaturessupportingbettercodeanalysis（suchasinnerclasses,StringBufferclass,optionalassertions,etc.）,andoptimizationsintheJavaVirtualMachineitself,suchasHotSpotbecomingthedefaultforSun'

sJVMin2000.Currently（November2011）,Java2.0codehasapproximatelyhalftheperformanceofCcode.[31]

SomeplatformsofferdirecthardwaresupportforJava;

therearemicrocontrollersthatcanrunJavainhardwareinsteadofasoftwareJVM,andARMbasedprocessorscanhavehardwaresupportforexecutingJavabytecodethroughitsJazelleoption.

Automaticmemorymanagement

Javausesanautomaticgarbagecollectortomanagememoryintheobjectlifecycle.Theprogrammerdetermineswhenobjectsarecreated,andtheJavaruntimeisresponsibleforrecoveringthememoryonceobjectsarenolongerinuse.Oncenoreferencestoanobjectremain,theunreachablememorybecomeseligibletobefreedautomaticallybythegarbagecollector.Somethingsimilartoamemoryleakmaystilloccurifaprogrammer'

scodeholdsareferencetoanobjectthatisnolongerneeded,typicallywhenobjectsthatarenolongerneededarestoredincontainersthatarestillinuse.Ifme