Java毕业设计外文翻译.docx

毕业设计（论文）外文文献翻译译文:JavaI/O系统对编程语言的设计者来说，创建,套好的输入输出（I/O）系统，是一项难度极高的任务。这一类可以从解决方案的数母之多上看出端倪。这个问题就难在它要面对的可能性太多了。不仅是因为有那么多的I/O的源和目的（文件，限制台，网络连接等等），而且还有许多方法（依次的，随机的，缓存的，二进制的，字符方式的，行的，字的等等）。Java类库的设计者们用“仓犍许多类”的方法来解决这个问题。坦率地说,JaVal/0系统的类实在太多了，以至于初看起来会把人吓着（但是，具有讽剌意味的是，这种设计事实上是限制了类的爆炸性增长此外，Java在1.0版之后又对其I/O类库进行了重大的修改，原先是面对byle的，现在又补充r面对CniCode字符的类库。为提高性能,完善功能,JDKl.4又加/一个nio（意思是“newI/O"。这个名字会用上许多年）。这么以来，假如你想对Java的I/O类库有个全面了解，并且做到运用白如，你就得先学习大量的类。此外，了解I/O类库的演化历史也是相当玳要的。可能你的第反应是“别拿什么历史来烦我了，告知我怎么用就可以了！”但问题是，假如你对这段一窍不通，很快就会被一些有用或是没用的类给搞糊涂了。本文会介绍JaVa标准类库中的各种I/O类，与其运用方法。File类在介绍干腌从流里读写数据的类之前，我们先介绍一下处理文件和书目的类。你会认为这是一个关于文件的类，但它不是。你可以用它来表示某个文件的名字，也可以用它来表示书目里一组文件的名字。假如它表示的是一组文件,那么你还可以用list（）方法来进行查询，让它会返回Slring数组。由于元素数量是固定的，因此数组会比容器更好一些。假如你想要获得另一个书1.l的清单，再建一个File对象就是了。书目列表器假设你想看看这个书目。有两个方法。一是不带参数调用list（）.它返回的是FilO对象所含内容的完整清单。但是，假如你要的是一个"限制性列表还是书目，以与删除文件。rena11eTo()这个方法会把文件重命名成(或者说移动到)新的书目，也就是参数所给出的书目。而参数本身就是一个FiIe对象。这个方法也适用于书目。输入与输出I/O类库常运用"流(Stream)”这种抽象。所谓"流"是一种能生成或接受数据的，代表数据的源和目标的对象。流把I/O设备内部的详细操作给隐微起来了。正如JDK文档所示的，Java的I/O类库分成输入和输出两大部分。全部InpulStreain和Reader的派生类都有一个基本的，继承下来的，能读取单个或byte数组的read()方法。同理,全部OutputStream和Writer的派生类都有一个基本的，能写入单个或byte数组的Write()方法。但通常状况下，你是不会去用这些方法的；它们是给其它类用的一一而后者会供应些更好用的接口。因此，你很少会遇到只用一个类就能创建一个流的情形，事实上你得把多个对象桎起来，并以此来获得所需的功能。Java的流类库之所以会那么让人犯旱，最主要的缘由就是"你必需为创建一个流而动用多个对象，我们最好还是依据其功能为这些class归个类。JaVa1.0的类库设计者们是从确定“让全部与输入相关的类去继承InPUIStream”入手的。同理，全部与输出相关的类就该继承OutputStream了。添加属性与适用的接口运用"分层对象(IayCredobjects)”,为单个对象动态地，透亮地添加功能的做法，被称为DecoralorPatterne(模式是ThinkinginPatterns(withJaVa)的主题。)Decoraor模式要求全部包覆在原始对象之外的对象，都必需具有与之完全相同的接口。这使得decorator的用法变得特别的透亮一无论对象是否被decorate过，传给它的消息总是相同的。这也是JaVal/0类库要有"filter(过滤器)”类的缘由:抽象的"filter”类是全部decorator的基类。(decorator必需具有与它要包装的对象的全部接口，但是decorator可以扩展这个接口，由此就衍生出了许多"filler"类)。Decorator模式常用于如下的情形：假如用继承来解决各种需求的话，类的数量会多到不切实际的地步。Java的I/O类库须要供应许多功能的组合，J：是decorator模式就有了用武之地。但是decorator有个缺点，在提高编程的敏捷性的同时(因为你能很简单地混合和匹配属性)，也使代码变得更困难了。Java的1/0类库之所以会这么怪，就是因为它"必需为一个1/0对象创建许多类”，也就是为一个"核心"I/O类加上许多decoratoro为InputStream和OutputStreani定义decorator类接口的类，分别是FiIterInputStream和FilterOutputStreamo这两个名字都起得不怎么样。FiIterInputStream和FilterOutputStream都继承自I/O类库的基类InputStream和OutputStrcani,这是decorator模式的关键(惟有这样decorator类的接口才能与它要服务的对象的完全相同)。用FilterInPUtStream读取InputStreamFilterInputStream与其派牛类有两项重要任务。DataInputStream可以读取各种PrimitiVe与String,(全部的方法都以"read"打头，比11readByte(),readFloat()它，以与它的搭档DataOUtPUtStreanb能让你通过流将primitive数据从一个地方导到另一个地方。这些"地方”都列在表12-4里。其它的类都是用来修改InPUtSIream的内部行为的：是不是做缓冲，是不是知道它所读取的行信息.(允许你读取行号或设定行号)，是不是会弹出单个字符。后两个看上去更像是给编译器用的(也就是说，它们也许是为Java编译器设计的)，所以通常状况下，你是不大会用到它们的。不论你用哪种1/0设备，输入的时候，最好都做缓冲.所以对"0类库来说，比校明智的做法还是把不缓冲当特例(或者去干脆调用方法)，而不是像现在这样把缓冲当作特例。外文原文：JAVA1/0SystemGreatingagoodinput/output(I/O)systemisoneofthemoredifficulttasksforthelanguagedesigner.Thisisevidencedbythenumberofdifferentapproaches.Thechallengeseemstobeincoveringal1eventualities.NotonlyaretheredifferentsourcesandsinksofI/Othatyouwanttocommunicatewith(files,theconsole,networkconnections),butyouneedtotalktotheminawidevarietyofways(sequential,random-access,buffered,binary,character,by1ines,bywords,etc.).TheJava1ibrarydesignersattackedthisproblembycreatinglotsofclasses.Infact,therearesomanyclassesforJava'SI/Osystemthatitcanbeintimidatingatfirst(ironically,theJavaI/Odesignactuallypreventsanexplosionofclasses).Therewasalsoasignificantchangeinthe1/0libraryafterJava1.0,whentheoriginalbyte-oriented1ibrarywassupplementedwithchar-oriented,Unicode-basedI/Oclasses.AsaresultthereareafairnumberofclassestolearnbeforeyouunderstandenoughofJava,SI/Opicturethatyoucanuseitproperly.Inaddilion,it,SratherimportanttounderstandtheevolutionhistoryoftheI/Olibrary,evenifyourfirstreactionis"don'tbothermewithhistory,justshowmehowtouseit!"Theproblemisthatwithoutthehistoricalperspectiveyouwillrapidlybecomeconfusedwithsomeoftheclassesandwhenyoushouldandshouldn,tusethem.ThisarticlewillgiveyouanintroductiontothevarietyofI/OclassesinthestandardJava1ibraryandhowtousethem.TheFileclassBeforegettingintotheclassesthatactualIyreadandwritedatatostreams,we'11lookautilityprovidedwiththelibrarytoassistyouinhandlingfiledirectoryissues.TheFileclasshasadeceivingname-youmightthinkitreferstoafile,butitdoesn,t.11canrepresenteiIherthenameofaparticularfileorthenamesofasetoffilesinadirectory.Ifit,Sasetoffiles,youcanaskfortheseiwiththe1ist()method,andthisreturnsanarrayofString.Itmakessensetoreturnanarrayratherthanoneoftheflexiblecontainerclassesbecausethenumberofelementsisfixed,andifyouwantadifferentdirectorylistingyoujustcreateadifferentFileobject.Infact,“FilePalh"wouldhavebeenabetternamefortheclass.Thissectionshowsanexampleoftheuseofthisclass,includingtheassociatedFilenameFilterinterface.AdirectorylisterSupposeyou'dliketoseeadirectorylisting.ThePileobjectcanbe1istedintwoways.Ifyoucalllist()withnoarguments,you,11gettheful1listthattheFiIeobjectcontains.However,ifyouwantarestrictedlist-forexample,ifyouwantallofthefileswithanextensionof.java-thenyouuseadirectoryfi1ter,"whichisaclassthattellshowtoselecttheFileobjectsfordisplay.TheDirFilterclass"inplemenls"theinterfaceFilenameFilter.It'susefultoseehowsimpletheFilenameFilterinterfaceis:publicinterfaceFilenameFillerbooleanaccept(Filetiir,Stringname);Theaccept()methodmustacceptaFileobjectrepresentingthedirectorythataparticularfileisfoundin,andaStringcontainingthenameofthatfile.YoumightchoosetouseorignoreeiIherofthesearguments,butyouwillprobablyatleastusethefilename.Rememberthatthe1ist()methodiscallingaccept()loreachofthefilenamesinthedirectoryobjecttoSeewhichoneshouldbeincluded-thisisindicatedbythebooleanresultreturnedbyaccept().Tomakesuretheelementyou,reworkingwithisonlythefilenameandcontainsnopathinformation,al1youhavetodoistaketheStringobjectandcreateaFileobjectoutofit,thencallgetName(),whichstripsawayal1thepathinformation(inaplatform-independenIway).Thenaccept()usesthearegularexpressionmatcherobjecttoseeiftheregularexpressionregexmatchesthenameofthefile.UsingacceptO,theIistOmethodreturnsanarray.AnonynousinnerclassesThisexampleisidealforrewritingusingananonymousinnerclass.safirstcul,amethodfi1ter()iscreatedthatreturnsareferencetoaFilenameFilter:/Usesanonymousinnerclasses.importjava.io.*:importjava,util.*;importcom.bruceeckel.util.*;publicclassDir1.ist2(publicstaticFilenameFilterfilter(finalStringafn)/Creationofanonym。USinnerclass:returnnewFiIenameFillerOl.Stringfn=afn;publicbooleanaccept(Filedir,Siringn)(/Strippathinformation:Stringf=newFile(n).getName();returnf.indexf(fn)!=-1:);/Endofanonymousinnerclasspublicstaticvoidmain(Stringargs)Filepath=newFile(".");Stringlist;if(args,length=0)list=path,list():elselist=path.1ist(filter(args0j);Arrays,sort(list,newAlphabeticComparatorO);for(inti=O:i<list,length：i+)System,out.println(listi):Notethattheargumenttofilter()mustbefinal.Thisisrequiredbytheanonymousinnerclasssothatitcanuseanobjectfromoutsideitsscope.ThisdesignisanimprovementbecausetheFilenameFilterclassisnowtightlyboundtoDir1.ist2.However,youcantakethisapproachonestepfurtheranddefinetheanonymousinnerclassasanargumenttolist(),inwhichcaseit,sevensmaller:/Buildingtheanonymousinnerclass”in-place.”importjava.io.*：importjava.util.*;importcom.bruceeckel.util.*;publicclassDir1.ist3publicstaticvoid11ain(finalSlringargs)Filepath=newFiIeStringlist：if(args,length=0)list=path.IislO：elselist=path.1isi(newFilenameFiIter()(publicbooleanaccept(Filedir,Siringn)(StringfnewFile(n).getName()：returnf.indexf(args0)!=-1;Arrays,sort(list,newAlphabelicComparatorO)：for(inti=O;i<list.length;i+)System,out.println(listi);Theargumenttomain()isnowfinal,sincetheanonymousinnerclassusesargs0jdirectly.Thisshowsyouhowanonymousinnerclassesallowthecreationofquick-and-(iirtyclassestosolveproblems.SinceeverythinginJavarevolvesaroundclasses,thiscanbeausefulcodingtechnique.OnebenefitisthatiIkeepsthecodethatsolvesaparticularproblemisolatedtogetherinonespot.Ontheotherhand,itisnotalwaysaseasytoread,soyoumustuseitjudiciously.CheckingforandcreatingdirectoriesTheFiIeclassismorethanjustarepresentationforanexistingfiIeordirectory.YoucanalsouseaFiIeobjecttocreateanewdirectoryoranentiredirectorypathifitdoesn,texist.Youcanalsolookatthecharacteristicsoffiles(size,lastmodificationdate,read/Write),seewhetheraFileobjectrepresentsafiIeoradirectory,anddeleteafile.Thefirstmethodthat'sexercisedbymain()isrenameTo(),whichallowsyoutorename(ormove)afiletoanentirelynewpathrepresentedbytheargument,whichisanotherFileobject.Thisalsoworkswithdirectoriesofanylength.InputandoutputI/Olibrariesoftenusetheabstractionofastream,whichrepresentsanydatasourceorsinkasanobjectcapableofproducingorreceivingpiecesofdata.ThestreamhidesthedetailsofwhathappenstothedatainsidetheactualI/Odevice.TheJava1ibraryclassesforI/Oaredividedbyinputandoutput,asyoucanseebylookingaltheonlineJavaclasshierarchyintheJDKdocumentation.Byinheritance,everythingderivedfromtheInputStreamorReaderclasseshavebasicmethodscalledread()forreadingasinglebyteorarrayofbytes.1.ikewise,everythingderivedfromOutputStreamorWriterclasseshavebasicmethodscalledwrite()forwritingasinglebyteorarrayofbytes.However,youwon'tgenerallyusethesemethods：theyexistsothatotherclassescanusethem-theseotherclassesprovideamoreusefulinterface.Thus,you,11rarelycreateyourstreamobjectbyusingasingleclass,bulinsteadwilllayermultipleobjectstogethertoprovideyourdesiredfunctionality.ThefactthatyoucreatemorethanoneobjecttocreateasingleresultingstreamistheprimaryreasonthatJava,Sstream1ibraryisconfusing.It,shelpfultocategorizetheclassesbytheirfundionality.InJava1.0,thelibrarydesignersstartedbydecidingthatallclassesthathadanythingtodowithinputwouldbeinheritedfromInputStreamandallclassesthatwereassociatedwithoutputwouldbeinheritedfromOutputStream.AddingattributesandusefulinterfacesTheuseoflayeredobjectstodynamicallyandtransparentlyaddresponsibilitiestoindividualobjectsisreferredtoastheDecoratorpattern.Thedecoratorpatternspecifiesthatal1objectsthatwraparoundyourinitialobjecthavethesameinterface.Thismakesthebasicuseofthedecoratorstransparent-yousendthesamemessagetoanobjectwhetherit,Sbeendecoratedornot.Thisisthereasonfortheexistenceofthe"filler"classesintheJavaI/Olibrary:theabstract“filter“classisthebaseclassforallthedecorators.(Adecoratormusthavethesameinterfaceastheobjectitdecorates,bulthedecoratorcanalsoextendtheinterface,whichoccursinseveralofthe"filler"classes).Decoratorsareoftenusedwhensimplesubclassingresultsinalargenumberofsubclassesinordertosatisfyeverypossiblecombinationthatisneeded-somanysubclassesthatitbecomesimpractical.TheJavaI/Olibraryrequiresmanydifferentcombinationsoffeatures,whichiswhythedecoratorpatternisused.Thereisadrawbacktothedecoratorpattern,however.DecoratorsgiveyoumuchmoreflexibilitywhiIeyou,rewritingaprogram(sinceyoucaneasilymixandmatchattributes),buttheyaddcomplexitytoyourcode.ThereasonthattheJavaI/O1ibraryisawkwardtouseisthatyoumustcreatemanyclasses-the"core"I/Otypeplusallthedecorators-inordertogetthesingleI/Oobjectthatyouwant.TheclassesthatprovidethedecoratorinterfacetocontrolaparticularInputStreamorOutputStreamaretheFilterInputStreaniandFiIterOuIputStream-whichdon,thaveveryintuitivenames.FilterInputStreamandFilterOutputStreamareabstractclassesthatarederivedfromthebaseclassesoftheI/O1ibrary,InputStreamandOutputStream,whichisthekeyrequirementofthedecorator(sothatitprovidesthecommoninterfacetoalltheobjectsthatarebeingdecorated).ReadingfromanInputStreamwithFilterInputStreaDTheFilterInputStreaniclassesaccomplishtwosignificantlydifferentthings.DataInputStreamallowsyoutoreaddifferenttypesofprimitivedataaswellasStringobjects.(Allthemethodsstartwith"read,“suchasreadByt(),readFloat(),etc.)This,alongwithiIscompanionDataOutputStreajn,allowsyoutomoveprimitivedatafromoneplacetoanotherviaastream.These“places"aredeterminedbytheclassesinTable12-4Table12-1.TypesofFilterInputStreanTheremainingclassesmodifythewayanInputStreambehavesinternally:whetherit,Sbufferedorunbuffered,ifitkeepstrackofthelinesit'sreading(allowingyoutoaskforlinenumbersorsetthelinenumber),andwhetheryoucanpushbackasinglecharacter.Thelasttwoclasseslookalot1ikesupportforbuiIdingaconpiIer(thatis,theywereaddedtosupporttheconstructionoftheJavacompiler),soyouprobablywon'tusethemingeneralprogramming.You,11probablyneedtobufferyourinputalmosteverytime,regardlessoftheI/Odeviceyou,reconnectingto,soitwou1dhavemademoresensefortheI/Olibrarytomakeaspecialcase(orsimplyamethodcall)forunbufferedinputratherthanbufferedinput.