外文翻译-Java(译文-英文)

JavaJavaI/O系统对编程语言的设计者来说，创建一套好的输入输出(I/O)系统，是一项难度极高的任务。这一点可以从解决方案的数量之多上看出端倪。这个问题难就难在它要面对的可能性太多了。不仅是因为有那么多I/O的源和目地(文件，控制台，网络连接等等)，而且还有很多方法(顺序的『sequential』，随机的『random-access』，缓存的『buffered』，二进制的『binary』，字符方式的『character』，行的『bylines』，字的『bywords』，等等)。Java类库的设计者们用"创建很多类"的办法来解决这个问题。坦率地说JavaI/O系统的类实在是太多了，以至于初看起来会把人吓着（但是，具有讽刺意味的是，这种设计实际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类库作了重大的修改，原先是面向byte的，现在又补充了面向Unicode字符的类库。为了提高性能，完善功能，JDK1.4又加了一个nio(意思是"newI/O"。这个名字会用上很多年)。这么以来，如果你想对Java的I/O类库有个全面了解，并且做到运用自如，你就得先学习大量的类。此外，了解I/O类库的演化的历史也是相当重要的。可能你的第一反应是"别拿什么历史来烦我了，告诉我怎么用就可以了！"但问题是，如果你对这段历史一无所知，很快就会被一些有用或是没用的类给搞糊涂了。本章会介绍Java标准类库中的各种I/O类，及其使用方法。File类在介绍直接从流里读写数据的类之前，我们先介绍一下处理文件和目录的类。File类有一个极具欺骗性的名字；或许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，也可以用它来表示目录里一组文件的名字。如果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String数组。由于元素数量是固定的，因此数组会比容器更好一些。如果你想要获取另一个目录的清单，再建一个File对象就是了。实际上，叫它"FilePath"可能会更好一些。下面我们举例说明怎样使用这个类及其相关的FilenameFilter接口。目录列表器假设你想看看这个目录。有两个办法。一是不带参数调用list()。它返回的是File对象所含内容的完整清单。但是，如果你要的是一个"限制性列表(restrictedlist)"的话——比方说，你想看看所有扩展名为.java的文件——那么你就得使用"目录过滤器"了。这是一个专门负责挑选显示File对象的内容的类。下面就是源代码。看看，用了java.utils.Arrays.sort()和11章的AlphabeticComparator之后，我们没费吹灰之力就对结果作了排序(按字母顺序)：//:c12:DirList.java//Displaysdirectorylistingusingregularexpressions.//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList{publicstaticvoidmain(String[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(newDirFilter(args[0]));Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}classDirFilterimplementsFilenameFilter{privatePatternpattern;publicDirFilter(Stringregex){pattern=Ppile(regex);}publicbooleanaccept(Filedir,Stringname){//Strippathinformation,searchforregex:returnpattern.matcher(newFile(name).getName()).matches();}}///:~DirFilter实现了FilenameFilter接口。我们来看看FilenameFilter究竟有多简单：publicinterfaceFilenameFilter{booleanaccept(Filedir,Stringname);}也就是说，这类对象的任务就是提供一个accept()的方法。之所以要创建这个类，就是要给list()提供一个accept()方法，这样当list()判断该返回哪些文件名的时候，能够"回过头来调用"accept()方法。因此，这种结构通常被称为回调(callback)。更准确地说，由于list()实现了基本功能，而FilenameFilter提供了"对外服务所需的算法"，因此这是一种"策略模式(StrategyPattern)"。由于list()拿FilenameFilter对象当参数，因此你可以将任何实现FilenameFilter接口的对象传给它，并以此(甚至是在运行时)控制list()的工作方式。回调能提高程序的灵活性。DirFilter还告诉我们，interface只是包含了一些方法，它没说你只能写这些方法。(但是，你至少要定义接口里有的方法。)这里我们还定义了DirFilter的构造函数。accept()方法需要两个参数，一个是File对象，表示这个文件是在哪个目录里面的；另一个是String，表示文件名。虽然你可以忽略它们中的一个，甚至两个都不管，但是你大概总得用一下文件名吧。记住，list()会对目录里的每个文件调用accept()，并以此判断是不是把它包括到返回值里；这个判断依据就是accept()的返回值。切记，文件名里不能有路径信息。为此你只要用一个String对象来创建File对象，然后再调用这个File对象的getName()就可以了。它会帮你剥离路径信息（以一种平台无关的方式）。然后再在accept()里面用正则表达式(regularexpression)的matcher对象判断，regex是否与文件名相匹配。兜完这个圈子，list()方法返回了一个数组。匿名内部类这是用匿名内部类(详见第八章)来重写程序的绝佳机会。下面我们先创建一个返回FilenameFilter的filter()方法。//:c12:DirList2.java//Usesanonymousinnerclasses.//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList2{publicstaticFilenameFilterfilter(finalStringregex){//Creationofanonymousinnerclass:returnnewFilenameFilter(){privatePatternpattern=Ppile(regex);publicbooleanaccept(Filedir,Stringname){returnpattern.matcher(newFile(name).getName()).matches();}};//Endofanonymousinnerclass}publicstaticvoidmain(String[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(filter(args[0]));Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}///:~注意，filter()的参数必须是final的。要想在匿名内部类里使用其作用域之外的对象，只能这么做。这是对前面所讲的代码的改进，现在FilenameFilter类已经与DirList2紧紧地绑在一起了。不过你还可以更进一步，把这个匿名内部类定义成list()的参数，这样代码会变得更紧凑：//:c12:DirList3.java//Buildingtheanonymousinnerclass"in-place."//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList3{publicstaticvoidmain(finalString[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(newFilenameFilter(){privatePatternpattern=Ppile(args[0]);publicbooleanaccept(Filedir,Stringname){returnpattern.matcher(newFile(name).getName()).matches();}});Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}///:~现在该轮到main()的参数成final了，因为匿名内部类要用它的arg[0]了。这个例子告诉我们，可以用匿名内部类来创建专门供特定问题用的，一次性的类。这种做法的好处是，它能把解决某个问题的代码全都集中到一个地方。但是从另一角度来说，这样做会使代码的可读性变差，所以要慎重。查看与创建目录File类的功能不仅限于显示文件或目录。它还能帮你创建新的目录甚至是目录路径(directorypath)，如果目录不存在的话。此外它还能用来检查文件的属性(大小，上次修改的日期，读写权限等)，判断File对象表示的是文件还是目录，以及删除文件。下面这段程序演示了File类的一些其他方法(请查阅JDK文档，以了解其全部功能)：//:c12:MakeDirectories.java//DemonstratestheuseoftheFileclassto//createdirectoriesandmanipulatefiles.//{Args:MakeDirectoriesTest}importcom.bruceeckel.simpletest.*;importjava.io.*;publicclassMakeDirectories{privatestaticTestmonitor=newTest();privatestaticvoidusage(){System.err.println("Usage:MakeDirectoriespath1...\n"+"Createseachpath\n"+"Usage:MakeDirectories-dpath1...\n"+"Deleteseachpath\n"+"Usage:MakeDirectories-rpath1path2\n"+"Renamesfrompath1topath2");System.exit(1);}privatestaticvoidfileData(Filef){System.out.println("Absolutepath:"+f.getAbsolutePath()+"\nCanread:"+f.canRead()+"\nCanwrite:"+f.canWrite()+"\ngetName:"+f.getName()+"\ngetParent:"+f.getParent()+"\ngetPath:"+f.getPath()+"\nlength:"+f.length()+"\nlastModified:"+f.lastModified());if(f.isFile())System.out.println("It'safile");elseif(f.isDirectory())System.out.println("It'sadirectory");}publicstaticvoidmain(String[]args){if(args.length<1)usage();if(args[0].equals("-r")){if(args.length!=3)usage();Fileold=newFile(args[1]),rname=newFile(args[2]);old.renameTo(rname);fileData(old);fileData(rname);return;//Exitmain}intcount=0;booleandel=false;if(args[0].equals("-d")){count++;del=true;}count--;while(++count<args.length){Filef=newFile(args[count]);if(f.exists()){System.out.println(f+"exists");if(del){System.out.println("deleting..."+f);f.delete();}}else{//Doesn'texistif(!del){f.mkdirs();System.out.println("created"+f);}}fileData(f);}if(args.length==1&&args[0].equals("MakeDirectoriesTest"))monitor.expect(newString[]{"%%(MakeDirectoriesTestexists"+"|createdMakeDirectoriesTest)","%%Absolutepath:"+"\\S+MakeDirectoriesTest","%%Canread:(true|false)","%%Canwrite:(true|false)","getName:MakeDirectoriesTest","getParent:null","getPath:MakeDirectoriesTest","%%length:\\d+","%%lastModified:\\d+","It'sadirectory"});}}///:~在fileData()演示了全套查询文件和目录路径信息的方法。main()的第一条指令就是执行renameTo()。它会把文件重命名成(或者说移动到)新的目录，也就是参数所给出的目录。而参数本身就是一个File对象。这个方法也适用于目录。如果你试过上面那段程序，就会发现，你能用它创建任意复杂的目录路径，因为mkdirs()已经帮你打理好了。输入与输出I/O类库常使用"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设备内部的具体操作给隐藏起来了。正如JDK文档所显示的，Java的I/O类库分成输入和输出两大部分。所有InputStream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，所有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。但通常情况下，你是不会去用这些方法的；它们是给其它类用的——而后者会提供一些更实用的接口。因此，你很少会碰到只用一个类就能创建一个流的情形，实际上你得把多个对象叠起来，并以此来获取所需的功能。Java的流类库之所以会那么让人犯晕，最主要的原因就是"你必须为创建一个流而动用多个对象"。我们最好还是根据其功能为这些class归个类。Java1.0的类库设计者们是从决定"让所有与输入相关的类去继承InputStream"入手的。同理，所有与输出相关的类就该继承OutputStream了。添加属性与适用的接口使用"分层对象(layeredobjects)"，为单个对象动态地，透明地添加功能的做法，被称为DecoratorPattern。(模式[61]是ThinkinginPatterns(withJava)的主题。)Decorator模式要求所有包覆在原始对象之外的对象，都必须具有与之完全相同的接口。这使得decorator的用法变得非常的透明--无论对象是否被decorate过，传给它的消息总是相同的。这也是JavaI/O类库要有"filter(过滤器)"类的原因：抽象的"filter"类是所有decorator的基类。(decorator必须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，由此就衍生出了很多"filter"类)。Decorator模式常用于如下的情形：如果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类库需要提供很多功能的组合，于是decorator模式就有了用武之地。[62]但是decorator有个缺点，在提高编程的灵活性的同时(因为你能很容易地混合和匹配属性)，也使代码变得更复杂了。Java的I/O类库之所以会这么怪，就是因为它"必须为一个I/O对象创建很多类"，也就是为一个"核心"I/O类加上很多decorator。为InputStream和OutputStream定义decorator类接口的类，分别是FilterInputStream和FilterOutputStream。这两个名字都起得不怎么样。FilterInputStream和FilterOutputStream都继承自I/O类库的基类InputStream和OutputStream，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及其派生类有两项重要任务。DataInputStream可以读取各种primitive及String。(所有的方法都以"read"打头，比如readByte()，readFloat())。它，以及它的搭档DataOutputStream，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12-1里。其它的类都是用来修改InputStream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，它们大概是为Java编译器设计的)，所以通常情况下，你是不大会用到它们的。不论你用哪种I/O设备，输入的时候，最好都做缓冲。所以对I/O类库来说，比较明智的做法还是把不缓冲当特例(或者去直接调用方法)，而不是像现在这样把缓冲当作特例。JAVATheJavaI/OSystemCreatingagoodinput/output(I/O)systemisoneofthemoredifficulttasksforthelanguagedesigner.Thisisevidencedbythenumberofdifferentapproaches.Thechallengeseemstobeincoveringalleventualities.NotonlyaretheredifferentsourcesandsinksofI/Othatyouwanttocommunicatewith(files,theconsole,networkconnections,etc.),butyouneedtotalktotheminawidevarietyofways(sequential,random-access,buffered,binary,character,bylines,bywords,etc.).TheJavalibrarydesignersattackedthisproblembycreatinglotsofclasses.Infact,therearesomanyclassesforJava’sI/Osystemthatitcanbeintimidatingatfirst(ironically,theJavaI/Odesignactuallypreventsanexplosionofclasses).TherewasalsoasignificantchangeintheI/OlibraryafterJava1.0,whentheoriginalbyte-orientedlibrarywassupplementedwithchar-oriented,Unicode-basedI/Oclasses.InJDK1.4,thenioclasses(for“newI/O,”anamewe’llstillbeusingyearsfromnow)wereaddedforimprovedperformanceandfunctionality.Asaresult,thereareafairnumberofclassestolearnbeforeyouunderstandenoughofJava’sI/Opicturethatyoucanuseitproperly.Inaddition,it’sratherimportanttounderstandtheevolutionhistoryoftheI/Olibrary,evenifyourfirstreactionis“don’tbothermewithhistory,justshowmehowtouseit!”Theproblemisthatwithoutthehistoricalperspective,youwillrapidlybecomeconfusedwithsomeoftheclassesandwhenyoushouldandshouldn’tusethem.ThischapterwillgiveyouanintroductiontothevarietyofI/OclassesinthestandardJavalibraryandhowtousethem.TheFileclassBeforegettingintotheclassesthatactuallyreadandwritedatatostreams,we’lllookatautilityprovidedwiththelibrarytoassistyouinhandlingfiledirectoryissues.TheFileclasshasadeceivingname;youmightthinkitreferstoafile,butitdoesn’t.Itcanrepresenteitherthenameofaparticularfileorthenamesofasetoffilesinadirectory.Ifit’sasetoffiles,youcanaskforthatsetusingthelist(

)method,whichreturnsanarrayofString.Itmakessensetoreturnanarrayratherthanoneoftheflexiblecontainerclasses,becausethenumberofelementsisfixed,andifyouwantadifferentdirectorylisting,youjustcreateadifferentFileobject.Infact,“FilePath”wouldhavebeenabetternamefortheclass.Thissectionshowsanexampleoftheuseofthisclass,includingtheassociatedFilenameFilterinterface.AdirectorylisterSupposeyou’dliketoseeadirectorylisting.TheFileobjectcanbelistedintwoways.Ifyoucalllist(

)withnoarguments,you’llgetthefulllistthattheFileobjectcontains.However,ifyouwantarestrictedlist—forexample,ifyouwantallofthefileswithanextensionof.java—thenyouusea“directoryfilter,”whichisaclassthattellshowtoselecttheFileobjectsfordisplay.Here’sthecodefortheexample.Notethattheresulthasbeeneffortlesslysorted(alphabetically)usingthejava.utils.Arrays.sort(

)methodandtheAlphabeticComparatordefinedinChapter11://:c12:DirList.java//Displaysdirectorylistingusingregularexpressions.//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList{publicstaticvoidmain(String[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(newDirFilter(args[0]));Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}classDirFilterimplementsFilenameFilter{privatePatternpattern;publicDirFilter(Stringregex){pattern=Ppile(regex);}publicbooleanaccept(Filedir,Stringname){//Strippathinformation,searchforregex:returnpattern.matcher(newFile(name).getName()).matches();}}///:~TheDirFilterclass“implements”theinterfaceFilenameFilter.It’susefultoseehowsimpletheFilenameFilterinterfaceis:publicinterfaceFilenameFilter{booleanaccept(Filedir,Stringname);}Itsaysallthatthistypeofobjectdoesisprovideamethodcalledaccept(

).Thewholereasonbehindthecreationofthisclassistoprovidetheaccept(

)methodtothelist(

)methodsothatlist(

)can“callback”accept(

)todeterminewhichfilenamesshouldbeincludedinthelist.Thus,thisstructureisoftenreferredtoasacallback.Morespecifically,thisisanexampleoftheStrategyPattern,becauselist(

)implementsbasicfunctionality,andyouprovidetheStrategyintheformofaFilenameFilterinordertocompletethealgorithmnecessaryforlist(

)toprovideitsservice.Becauselist(

)takesaFilenameFilterobjectasitsargument,itmeansthatyoucanpassanobjectofanyclassthatimplementsFilenameFiltertochoose(evenatruntime)howthelist(

)methodwillbehave.Thepurposeofacallbackistoprovideflexibilityinthebehaviorofcode.DirFiltershowsthatjustbecauseaninterfacecontainsonlyasetofmethods,you’renotrestrictedtowritingonlythosemethods.(Youmustatleastprovidedefinitionsforallthemethodsinaninterface,however.)Inthiscase,theDirFilterconstructorisalsocreated.Theaccept(

)methodmustacceptaFileobjectrepresentingthedirectorythataparticularfileisfoundin,andaStringcontainingthenameofthatfile.Youmightchoosetouseorignoreeitherofthesearguments,butyouwillprobablyatleastusethefilename.Rememberthatthelist(

)methodiscallingaccept(

)foreachofthefilenamesinthedirectoryobjecttoseewhichoneshouldbeincluded;thisisindicatedbythebooleanresultreturnedbyaccept(

).Tomakesuretheelementyou’reworkingwithisonlythefilenameandcontainsnopathinformation,allyouhavetodoistaketheStringobjectandcreateaFileobjectoutofit,thencallgetName(

),whichstripsawayallthepathinformation(inaplatform-independentway).Thenaccept(

)usesaregularexpressionmatcherobjecttoseeiftheregularexpressionregexmatchesthenameofthefile.Usingaccept(

),thelist(

)methodreturnsanarray.AnonymousinnerclassesThisexampleisidealforrewritingusingananonymousinnerclass(describedinChapter8).Asafirstcut,amethodfilter(

)iscreatedthatreturnsareferencetoaFilenameFilter://:c12:DirList2.java//Usesanonymousinnerclasses.//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList2{publicstaticFilenameFilterfilter(finalStringregex){//Creationofanonymousinnerclass:returnnewFilenameFilter(){privatePatternpattern=Ppile(regex);publicbooleanaccept(Filedir,Stringname){returnpattern.matcher(newFile(name).getName()).matches();}};//Endofanonymousinnerclass}publicstaticvoidmain(String[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(filter(args[0]));Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}///:~Notethattheargumenttofilter(

)mustbefinal.Thisisrequiredbytheanonymousinnerclasssothatitcanuseanobjectfromoutsideitsscope.ThisdesignisanimprovementbecausetheFilenameFilterclassisnowtightlyboundtoDirList2.However,youcantakethisapproachonestepfurtheranddefinetheanonymousinnerclassasanargumenttolist(

),inwhichcaseit’sevensmaller://:c12:DirList3.java//Buildingtheanonymousinnerclass"in-place."//{Args:"D.*\.java"}importjava.io.*;importjava.util.*;importjava.util.regex.*;importcom.bruceeckel.util.*;publicclassDirList3{publicstaticvoidmain(finalString[]args){Filepath=newFile(".");String[]list;if(args.length==0)list=path.list();elselist=path.list(newFilenameFilter(){privatePatternpattern=Ppile(args[0]);publicbooleanaccept(Filedir,Stringname){returnpattern.matcher(newFile(name).getName()).matches();}});Arrays.sort(list,newAlphabeticComparator());for(inti=0;i<list.length;i++)System.out.println(list[i]);}}///:~Theargumenttomain(

)isnowfinal,sincetheanonymousinnerclassusesargs[0]directly.Thisshowsyouhowanonymousinnerclassesallowthecreationofspecific,one-offclassestosolveproblems.Onebenefitofthisapproachisthatitkeepsthecodethatsolvesaparticularproblemisolatedtogetherinonespot.Ontheotherhand,itisnotalwaysaseasytoread,soyoumustuseitjudiciously.CheckingforandcreatingdirectoriesTheFileclassismorethanjustarepresentationforanexistingfileordirectory.YoucanalsouseaFileobjecttocreateanewdirectoryoranentiredirectorypathifitdoesn’texist.Youcanalsolookatthecharacteristicsoffiles(size,lastmodificationdate,read/write),seewhetheraFileobjectrepresentsafileoradirectory,anddeleteafile.ThisprogramshowssomeoftheothermethodsavailablewiththeFileclass(seetheHTMLdocumentationfromforthefullset)://:c12:MakeDirectories.java//DemonstratestheuseoftheFileclassto//createdirectoriesandmanipulatefiles.//{Args:MakeDirectoriesTest}importcom.bruceeckel.simpletest.*;importjava.io.*;publicclassMakeDirectories{privatestaticTestmonitor=newTest();privatestaticvoidusage(){System.err.println("Usage:MakeDirectoriespath1...\n"+"Createseachpath\n"+"Usage:MakeDirectories-dpath1...\n"+"Deleteseachpath\n"+"Usage:MakeDirectories-rpath1path2\n"+"Renamesfrompath1topath2");System.exit(1);}privatestaticvoidfileData(Filef){System.out.println("Absolutepath:"+f.getAbsolutePath()+"\nCanread:"+f.canRead()+"\nCanwrite:"+f.canWrite()+"\ngetName:"+f.getName()+"\ngetParent:"+f.getParent()+"\ngetPath:"+f.getPath()+"\nlength:"+f.length()+"\nlastModified:"+f.lastModified());if(f.isFile())System.out.println("It'safile");elseif(f.isDirectory())System.out.println("It'sadirectory");}publicstaticvoidmain(String[]args){if(args.length<1)usage();if(args[0].equals("-r")){if(args.length!=3)usage();Fileold=newFile(args[1]),rname=newFile(args[2]);old.renameTo(rname);fileData(old);fileData(rname);return;//Exitmain}intcount=0;booleandel=false;if(args[0].equals("-d")){count++;del=true;}count--;while(++count<args.length){Filef=newFile(args[count]);if(f.exists()){System.out.println(f+"exists");if(del){System.out.println("deleting..."+f);f.delete();}}else{//Doesn'texistif(!del){f.mkdirs();System.out.println("created"+f);}}fileData(f);}if(args.length==1&&args[0].equals("MakeDirectoriesTest"))monitor.expect(newString[]{"%%(MakeDirectoriesTestexists"+"|createdMakeDirectoriesTest)","%%Absolutepath:"+"\\S+MakeDirectoriesTest","%%Canread:(true|false)","%%Canwrite:(true|false)","getName:MakeDirectoriesTest","getParent:null","getPath:MakeDirectoriesTest","%%length:\\d+","%%lastModified:\\d+","It'sadirectory"});}}///:~InfileData(

)youcanseevariousfileinvestigationmethodsusedtodisplayinformationaboutthefileordirectorypath.Thefirstmethodthat’sexercisedbymain(

)isrenameTo(

),whichallowsyoutorename(ormove)afiletoanentirelynewpathrepresentedbytheargument,whichisanotherFileobject.Thisalsoworkswithdirectoriesofanylength.Ifyouexperimentwiththeprecedingprogram,you’llfindthatyoucanmakeadirectorypathofanycomplexity,becausemkdirs(

)willdoalltheworkforyou.InputandoutputI/Olibrariesoftenusetheabstractionofastream,whichrepresentsanydatasourceorsinkasanobjectcapableofproducingorreceivingpiecesofdata.ThestreamhidesthedetailsofwhathappenstothedatainsidetheactualI/Odevice.TheJavalibraryclassesforI/Oaredividedbyinputandoutput,asyoucanseebylookingattheclasshierarchyintheJDKdocumentation.Byinheritance,everythingderivedfromtheInputStreamorReaderclasseshavebasicmethodscalledread(

)forreadingasinglebyteorarrayofbytes.Likewise,everythingderivedfromOutputStreamorWriterclasseshavebasicmethodscalledwrite(

)forwritingasinglebyteorarrayofbytes.However,youwon’tgenerallyusethesemethods;theyexistsothatotherclassescanusethem—theseotherclassesprovideamoreusefulinterface.Thus,you’llrarelycreateyourstreamobjectbyusingasingleclass,butinsteadwilllayermultipleobjectstogethertoprovideyourdesiredfunctionality.ThefactthatyoucreatemorethanoneobjecttocreateasingleresultingstreamistheprimaryreasonthatJava’sstreamlibraryisconfusing.It’shelpfultocategorizetheclassesbytheirfunctionality.InJava1.0,thelibrarydesignersstartedbydecidingthatallclassesthathadanythingtodowithinputwouldbeinheritedfromInputStream,andallclassesthatwereassociatedwithoutputwouldbeinheritedfromOutputStream.Addingattributes

andusefulinterfacesTheuseoflayeredobjectstodynamicallyandtransparentlyaddresponsibilitiestoindividualobjectsisreferredtoastheDecoratorpattern.(Patterns[61]arethesubjectofThinkinginPatterns(withJava)atwww.BruceE.)Thedecoratorpatternspecifiesthatallobjectsthatwraparoundyourinitialobjecthavethesameinterface.Thismakesthebasicuseofthedecoratorstransparent—yousendthesamemessagetoanobjectwhetherithasbeendecoratedornot.Thisisthereasonfortheexistenceofthe“filter”classesintheJavaI/Olibrary:Theabstract“filter”classisthebaseclassforallthedecorators.(Adecoratormusthavethesameinterfaceastheobjectitdecorates,butthedecoratorcanalsoextendtheinterface,whichoccursinseveralofthe“filter”classes).Decoratorsareoftenusedwhensimplesubclassingresultsinalargenumberofclassesinordertosatisfyeverypossiblecombinationthatisneeded—somanyclassesthatitbecomesimpractical.TheJavaI/Olibraryrequiresmanydifferentcombinationsoffeatures,andthisisthejustificationforusingthedecoratorpattern.[62]Thereisadrawbacktothedecoratorpattern,however.Decoratorsgiveyoumuchmoreflexibilitywhileyou’rewritingaprogram(sinceyoucaneasilymixandmatchattributes),buttheyaddcomplexitytoyourcode.ThereasonthattheJavaI/Olibraryisawkwardtouseisthatyoumustcreatemanyclasses—the“core”I/Otypeplusallthedecorators—inordertogetthesingleI/Oobjectthatyouwant.TheclassesthatprovidethedecoratorinterfacetocontrolaparticularInputStreamorOutputStreamaretheFilterInputStreamandFilterOutputStream,whichdon’thaveveryintuitivenames.FilterInputStreamandFilterOutputStreamarederivedfromthebaseclassesoftheI/Olibrary,InputStreamandOutputStream,whichisthekeyrequirementofthedecorator(sothatitprovidesthecommoninterfacetoalltheobjectsthatarebeingdecorated).ReadingfromanInputStream

withFilterInputStreamTheFilterInputStreamclassesaccomplishtwosignificantlydifferentthings.DataInputStreamallowsyoutoreaddifferenttypesofprimitivedataaswellasStringobjects.(Allthemethodsstartwith“read,”suchasreadByte(

),readFloat(

),etc.)This,alongwithitscompanionDataOutputStream,allowsyoutomoveprimitivedatafromoneplacetoanotherviaastream.These“places”aredeterminedbytheclassesinTable12-1.TheremainingclassesmodifythewayanInputStreambehavesinternally:whetherit’sbufferedorunbuffered,ifitkeepstrackofthelinesit’sreading(allowingyoutoaskforlinenumbersorsetthelinenumber),andwhetheryoucanpushbackasinglecharacter.Thelasttwoclasseslookalotlikesupportforbuildingacompiler(thatis,theywereprobablyaddedtosupporttheconstructionoftheJavacompiler),soyouprobablywon’tusethemingeneralprogramming.You’llneedtobufferyourinputalmosteverytime,regardlessoftheI/Odeviceyou’reconnectingto,soitwouldhavemademoresensefortheI/Olibrarytomakeaspecialcase(orsimplyamethodcall)forunbufferedinputratherthan