Java语言程序设计10E LiangPPT习题案例17slide.ppt

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1、1Chapter17BinaryI/O2MotivationsDatastoredinatextfileisrepresentedinhuman-readableform.Datastoredinabinaryfileisrepresentedinbinaryform.Youcannotreadbinaryfiles.Theyaredesignedtobereadbyprograms.Forexample,Javasourceprogramsarestoredintextfilesandcanbe

2、readbyatexteditor,butJavaclassesarestoredinbinaryfilesandarereadbytheJVM.Theadvantageofbinaryfilesisthattheyaremoreefficienttoprocessthantextfiles.3ObjectivesTodiscoverhowI/OisprocessedinJava(§17.2).TodistinguishbetweentextI/OandbinaryI/O(§17.3).Torea

3、dandwritebytesusingFileInputStreamandFileOutputStream(§17.4.1).ToreadandwriteprimitivevaluesandstringsusingDataInputStream/DataOutputStream(§17.4.3).TostoreandrestoreobjectsusingObjectOutputStreamandObjectInputStream,andtounderstandhowobjectsareserial

4、izedandwhatkindofobjectscanbeserialized(§17.6).ToimplementtheSerializableinterfacetomakeobjectsserializable(§17.6.1).Toserializearrays(§17.6.2).ToreadandwritethesamefileusingtheRandomAccessFileclass(§17.7).4HowisI/OHandledinJava?AFileobjectencapsulate

5、sthepropertiesofafileorapath,butdoesnotcontainthemethodsforreading/writingdatafrom/toafile.InordertoperformI/O,youneedtocreateobjectsusingappropriateJavaI/Oclasses.PrintWriteroutput=newPrintWriter("temp.txt");output.println("Java101");output.close();S

6、cannerinput=newScanner(newFile("temp.txt"));System.out.println(input.nextLine());5TextFilevs.BinaryFileDatastoredinatextfilearerepresentedinhuman-readableform.Datastoredinabinaryfilearerepresentedinbinaryform.Youcannotreadbinaryfiles.Binaryfilesaredes

7、ignedtobereadbyprograms.Forexample,theJavasourceprogramsarestoredintextfilesandcanbereadbyatexteditor,buttheJavaclassesarestoredinbinaryfilesandarereadbytheJVM.Theadvantageofbinaryfilesisthattheyaremoreefficienttoprocessthantextfiles.Althoughitisnotte

8、chnicallypreciseandcorrect,youcanimaginethatatextfileconsistsofasequenceofcharactersandabinaryfileconsistsofasequenceofbits.Forexample,thedecimalinteger199isstoredasthesequenceofthreecharacters:'1','9','9'inatextfileandthesameintegerisstoredas