java语言程序设计-基础篇-课件(第1章)英文VIP

Chapter1IntroductiontoComputers,Programs,andJava1ObjectivesToreviewcomputerbasics,programs,andoperatingsystems(§§1.2-1.4).ToexploretherelationshipbetweenJavaandtheWorldWideWeb(§1.5).TodistinguishthetermsAPI,IDE,andJDK(§1.6).TowriteasimpleJavaprogram(§1.7).Todisplayoutputontheconsole(§1.7).ToexplainthebasicsyntaxofaJavaprogram(§1.7).Tocreate,compile,andrunJavaprograms(§1.8).(GUI)TodisplayoutputusingtheJOptionPaneoutputdialogboxes(§1.9).2WhatisaComputer?AcomputerconsistsofaCPU,memory,harddisk,floppydisk,monitor,printer,andcommunicationdevices.3CPUThecentralprocessingunit(CPU)isthebrainofacomputer.Itretrievesinstructionsfrommemoryandexecutesthem.TheCPUspeedismeasuredinmegahertz(MHz),with1megahertzequaling1millionpulsespersecond.ThespeedoftheCPUhasbeenimprovedcontinuously.IfyoubuyaPCnow,youcangetanIntelPentium4Processorat3gigahertz(1gigahertzis1000megahertz).4MemoryMemoryistostoredataandprograminstructionsforCPUtoexecute.Amemoryunitisanorderedsequenceofbytes,eachholdseightbits.Aprogramanditsdatamustbebroughttomemorybeforetheycanbeexecuted.Amemorybyteisneverempty,butitsinitialcontentmaybemeaninglesstoyourprogram.Thecurrentcontentofamemorybyteislostwhenevernewinformationisplacedinit.5HowDataisStored?Dataofvariouskinds,suchasnumbers,characters,andstrings,areencodedasaseriesofbits(zerosandones).Computersusezerosandonesbecausedigitaldeviceshavetwostablestates,whicharereferredtoaszeroandonebyconvention.Theprogrammersneednottobeconcernedabouttheencodinganddecodingofdata,whichisperformedautomaticallybythesystembasedontheencodingscheme.Theencodingschemevaries.Forexample,character‘J’isrepresentedby01001010inonebyte.Asmallnumbersuchasthreecanbestoredinasinglebyte.Ifcomputerneedstostorealargenumberthatcannotfitintoasinglebyte,itusesanumberofadjacentbytes.Notwodatacanshareorsplitasamebyte.Abyteistheminimumstorageunit.6StorageDevicesMemoryisvolatile,becauseinformationislostwhenthepowerisoff.Programsanddataarepermanentlystoredonstoragedevicesandaremovedtomemorywhenthecomputeractuallyusesthem.Therearethreemaintypesofstoragedevices:Diskdrives(harddisksandfloppydisks),CDdrives(CD-RandCD-RW),andTapedrives.7OutputDevices:MonitorThemonitordisplaysinformation(textandgraphics).Theresolutionanddotpitchdeterminethequalityofthedisplay.

8MonitorResolutionandDotPitchTheresolutionspecifiesthenumberofpixelspersquareinch.Pixels(shortfor“pictureelements”)aretinydotsthatformanimageonthescreen.Theresolutioncanbesetmanually.Thehighertheresolution,thesharperandclearertheimageis.However,theimagemaybeverysmallifyousethighresolutiononasmallscreenmonitor.PCmonitorsareusually15-inch,17-inch,19-inch,or21-inch.Fora15-inchmonitor,acomfortableresolutionsettingwouldbe640

480(307,200pixels).resolutionThedotpitchistheamountofspacebetweenpixels.Thesmallerthedotpitch,thebetterthedisplay.

dotpitch9CommunicationDevicesAregularmodemusesaphonelineandcantransferdatainaspeedupto56,000bps(bitspersecond).ADSL(digitalsubscriberline)alsousesaphonelineandcantransferdatainaspeed20timesfasterthanaregularmodem.AcablemodemusestheTVcablelinemaintainedbythecablecompany.AcablemodemisasfastasaDSL.Networkinterfacecard(NIC)isadevicetoconnectacomputertoalocalareanetwork(LAN).TheLANiscommonlyusedinbusiness,universities,andgovernmentorganizations.AtypicaltypeofNIC,called10BaseT,cantransferdataat10mbps(millionbitspersecond).10ProgramsComputerprograms,knownassoftware,areinstructionstothecomputer.

Youtellacomputerwhattodothroughprograms.Withoutprograms,acomputerisanemptymachine.Computersdonotunderstandhumanlanguages,soyouneedtousecomputerlanguagestocommunicatewiththem.Programsarewrittenusingprogramminglanguages.11ProgrammingLanguagesMachineLanguageAssemblyLanguageHigh-LevelLanguageMachinelanguageisasetofprimitiveinstructionsbuiltintoeverycomputer.Theinstructionsareintheformofbinarycode,soyouhavetoenterbinarycodesforvariousinstructions.Programwithnativemachinelanguageisatediousprocess.Moreovertheprogramsarehighlydifficulttoreadandmodify.Forexample,toaddtwonumbers,youmightwriteaninstructioninbinarylikethis:

110110101001101012ProgrammingLanguagesMachineLanguageAssemblyLanguageHigh-LevelLanguageAssemblylanguagesweredevelopedtomakeprogrammingeasy.Sincethecomputercannotunderstandassemblylanguage,however,aprogramcalledassemblerisusedtoconvertassemblylanguageprogramsintomachinecode.Forexample,toaddtwonumbers,youmightwriteaninstructioninassemblycodelikethis:ADDF3R1,R2,R313ProgrammingLanguagesMachineLanguageAssemblyLanguageHigh-LevelLanguageThehigh-levellanguagesareEnglish-likeandeasytolearnandprogram.Forexample,thefollowingisahigh-levellanguagestatementthatcomputestheareaofacirclewithradius5:area=5*5*3.1415;

14PopularHigh-LevelLanguagesCOBOL(COmmonBusinessOrientedLanguage)FORTRAN(FORmulaTRANslation)BASIC(BeginnerAll-purposeSymbolicInstructionalCode)Pascal(namedforBlaisePascal)Ada(namedforAdaLovelace)C(whosedeveloperdesignedBfirst)

VisualBasic(Basic-likevisuallanguagedevelopedbyMicrosoft)Delphi(Pascal-likevisuallanguagedevelopedbyBorland)C++(anobject-orientedlanguage,basedonC)C#(aJava-likelanguagedevelopedbyMicrosoft)Java(Weuseitinthebook)15CompilingSourceCodeAprogramwritteninahigh-levellanguageiscalledasourceprogram.Sinceacomputercannotunderstandasourceprogram.Programcalledacompilerisusedtotranslatethesourceprogramintoamachinelanguageprogramcalledanobjectprogram.Theobjectprogramisoftenthenlinkedwithothersupportinglibrarycodebeforetheobjectcanbeexecutedonthemachine.16OperatingSystemsTheoperatingsystem(OS)isaprogramthatmanagesandcontrolsacomputer’sactivities.YouareprobablyusingWindows98,NT,2000,XP,orME.WindowsiscurrentlythemostpopularPCoperatingsystem.ApplicationprogramssuchasanInternetbrowserandawordprocessorcannotrunwithoutanoperatingsystem.17WhyJava?TheansweristhatJavaenablesuserstodevelopanddeployapplicationsontheInternetforservers,desktopcomputers,andsmallhand-helddevices.ThefutureofcomputingisbeingprofoundlyinfluencedbytheInternet,andJavapromisestoremainabigpartofthatfuture.JavaistheInternetprogramminglanguage.Javaisageneralpurposeprogramminglanguage.JavaistheInternetprogramminglanguage.18Java,Web,andBeyondJavacanbeusedtodevelopWebapplications.JavaAppletsJavaWebApplicationsJavacanalsobeusedtodevelopapplicationsforhand-helddevicessuchasPalmandcellphones19ExamplesofJava’sVersatility(Applets)20PDAandCellPhone21Java’sHistoryJamesGoslingandSunMicrosystemsOakJava,May20,1995,SunWorldHotJavaThefirstJava-enabledWebbrowserEarlyHistoryWebsite:/features/1998/05/birthday.html22CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicCompanionWebsite/liang/intro8e/JavaCharacteristics.pdf23CharacteristicsofJavaJavaIsSimple

JavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicJavaispartiallymodeledonC++,butgreatlysimplifiedandimproved.SomepeoplerefertoJavaas"C++--"becauseitislikeC++butwithmorefunctionalityandfewernegativeaspects.CompanionWebsite24CharacteristicsofJavaJavaIsSimpleJavaIsObject-Oriented

JavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicJavaisinherentlyobject-oriented.Althoughmanyobject-orientedlanguagesbeganstrictlyasprocedurallanguages,Javawasdesignedfromthestarttobeobject-oriented.Object-orientedprogramming(OOP)isapopularprogrammingapproachthatisreplacingtraditionalproceduralprogrammingtechniques.Oneofthecentralissuesinsoftwaredevelopmentishowtoreusecode.Object-orientedprogrammingprovidesgreatflexibility,modularity,clarity,andreusabilitythroughencapsulation,inheritance,andpolymorphism.CompanionWebsite25CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributed

JavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicDistributedcomputinginvolvesseveralcomputersworkingtogetheronanetwork.Javaisdesignedtomakedistributedcomputingeasy.SincenetworkingcapabilityisinherentlyintegratedintoJava,writingnetworkprogramsislikesendingandreceivingdatatoandfromafile.

CompanionWebsite26CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpreted

JavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicYouneedaninterpretertorunJavaprograms.TheprogramsarecompiledintotheJavaVirtualMachinecodecalledbytecode.Thebytecodeismachine-independentandcanrunonanymachinethathasaJavainterpreter,whichispartoftheJavaVirtualMachine(JVM).CompanionWebsite27CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobust

JavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicJavacompilerscandetectmanyproblemsthatwouldfirstshowupatexecutiontimeinotherlanguages.Javahaseliminatedcertaintypesoferror-proneprogrammingconstructsfoundinotherlanguages.Javahasaruntimeexception-handlingfeaturetoprovideprogrammingsupportforrobustness.CompanionWebsite28CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecure

JavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicJavaimplementsseveralsecuritymechanismstoprotectyoursystemagainstharmcausedbystrayprograms.CompanionWebsite29CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-Neutral

JavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamicWriteonce,runanywhereWithaJavaVirtualMachine(JVM),youcanwriteoneprogramthatwillrunonanyplatform.CompanionWebsite30CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortable

Java'sPerformanceJavaIsMultithreadedJavaIsDynamicBecauseJavaisarchitectureneutral,Javaprogramsareportable.Theycanberunonanyplatformwithoutbeingrecompiled.CompanionWebsite31CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformance

JavaIsMultithreadedJavaIsDynamicJava’sperformanceBecauseJavaisarchitectureneutral,Javaprogramsareportable.Theycanberunonanyplatformwithoutbeingrecompiled.CompanionWebsite32CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreaded

JavaIsDynamicMultithreadprogrammingissmoothlyintegratedinJava,whereasinotherlanguagesyouhavetocallproceduresspecifictotheoperatingsystemtoenablemultithreading.CompanionWebsite33CharacteristicsofJavaJavaIsSimpleJavaIsObject-OrientedJavaIsDistributedJavaIsInterpretedJavaIsRobustJavaIsSecureJavaIsArchitecture-NeutralJavaIsPortableJava'sPerformanceJavaIsMultithreadedJavaIsDynamic

Javawasdesignedtoadapttoanevolvingenvironment.Newcodecanbeloadedontheflywithoutrecompilation.Thereisnoneedfordeveloperstocreate,andforuserstoinstall,majornewsoftwareversions.Newfeaturescanbeincorporatedtransparentlyasneeded.

CompanionWebsite34JDKVersionsJDK1.02(1995)JDK1.1(1996)JDK1.2(1998)JDK1.3(2000)JDK1.4(2002)JDK1.5(2004)a.k.a.JDK5orJava5JDK1.6(2006)a.k.a.JDK6orJava6JDK1.7(possibly2010)a.k.a.JDK7orJava735JDKEditionsJavaStandardEdition(J2SE)J2SEcanbeusedtodevelopclient-sidestandaloneapplicationsorapplets.JavaEnterpriseEdition(J2EE)J2EEcanbeusedtodevelopserver-sideapplicationssuchasJavaservletsandJavaServerPages.JavaMicroEdition(J2ME).J2MEcanbeusedtodevelopapplicationsformobiledevicessuchascellphones.ThisbookusesJ2SEtointroduceJavaprogramming.

36PopularJavaIDEsNetBeansOpenSourcebySunEclipseOpenSourcebyIBM37ASimpleJavaProgram//ThisprogramprintsWelcometoJava!publicclassWelcome{ publicstaticvoidmain(String[]args){System.out.println("WelcometoJava!");}}RunWelcomeListing1.1IMPORTANTNOTE:(1)Toenablethebuttons,youmustdownloadtheentireslidefileslide.zipandunzipthefilesintoadirectory(e.g.,c:\slide).(2)YoumusthaveinstalledJDKandsetJDK’sbindirectoryinyourenvironmentpath(e.g.,c:\ProgramFiles\java\jdk1.6.0_14\bininyourenvironmentpath.38CreatingandEditingUsingNotePadTouseNotePad,typenotepadWelcome.javafromtheDOSprompt.39CreatingandEditingUsingWordPadTouseWordPad,typewriteWelcome.javafromtheDOSprompt.40Creating,Compiling,andRunningPrograms41CompilingJavaSourceCodeYoucanportasourceprogramtoanymachinewithappropriatecompilers.Thesourceprogrammustberecompiled,however,becausetheobjectprogramcanonlyrunonaspecificmachine.Nowadayscomputersarenetworkedtoworktogether.Javawasdesignedtorunobjectprogramsonanyplatform.WithJava,youwritetheprogramonce,andcompilethesourceprogramintoaspecialtypeofobjectcode,knownasbytecode.ThebytecodecanthenrunonanycomputerwithaJavaVirtualMachine,asshownbelow.JavaVirtualMachineisasoftwarethatinterpretsJavabytecode.42TraceaProgramExecution//ThisprogramprintsWelcometoJava!publicclassWelcome{ publicstaticvoidmain(String[]args){System.out.println("WelcometoJava!");}}Entermainmethodanimation43TraceaProgramExecution//ThisprogramprintsWelcometoJava!publicclassWelcome{ publicstaticvoidmain(String[]args){System.out.println("WelcometoJava!");}}Executestatementanimation44TraceaProgramExecution//ThisprogramprintsWelcometoJava!publicclassWelcome{ publicstaticvoidmain(String[]args){System.out.println("WelcometoJava!");}}animationprintamessagetotheconsole45TwoMoreSimpleExamplesRunWelcome1RunComputeExpression46SupplementsontheCompanionWebsiteSeeSupplementI.BforinstallingandconfiguringJDKSeeSupplementI.CforcompilingandrunningJavafromthecommandwindowfordetails/liang/intro8eCompanionWebsite47CompilingandRunningJavafromtheCommandWindowSetpathtoJDKbindirectorysetpath=c:\ProgramFiles\java\jdk1.6.0\binSetclasspathtoincludethecurrentdirectorysetclasspath=.CompilejavacWelcome.javaRunjavaWelcomeCompanionWebsite48CompilingandRunningJavafromTextPadSeeSupplementII.AontheWebsitefordetailsCompanionWebsite49CompilingandRunningJavafromJBuilderSeeSupplementII.HontheWebsitefordetailsCompanionWebsite50CompilingandRunningJavafromNetBeansSeeSupplementI.DontheWebsitefordetailsCompanionWebsite51AnatomyofaJavaProgramCommentsReservedwordsModifiersStatementsBlocksClassesMethodsThemainmethod52CommentsLinecomment:Alinecommentisprecededbytwoslashes(//)inaline.Paragraphcomment:Aparagraphcommentisenclosedbetween/*and*/inoneormultiplelines.javadoccomment:javadoccommentsbeginwith/**andendwith*/.Theyareusedfordocumentingclasses,data,andmethods.TheycanbeextractedintoanHTMLfileusingJDK'sjavadoccommand.ThreetypesofcommentsinJava.53ReservedWordsReservedwordsorkeywordsarewordsthathaveaspecificmeaningtothecompilerandcannotbeusedforotherpurposesintheprogram.Forexample,whenthecompilerseesthewordclass,itunderstandsthatthewordafterclassisthenamefortheclass.OtherreservedwordsinListing1.1arepublic,static,andvoid.Theirusewillbeintroducedlaterinthebook.54ModifiersJavausescertainreservedwordscalledmodifiersthatspecifythepropertiesofthedata,methods,andclassesandhowtheycanbeused.Examplesofmodifiersarepublicandstatic.Othermodifiersareprivate,final,abstract,andprotected.Apublicdatum,method,orclasscanbeaccessedbyotherprograms.Aprivatedatumormethodcannotbeaccessedbyotherprograms.ModifiersarediscussedinChapter6,“ObjectsandClasses.”55StatementsAstatementrepresentsanactionorasequenceofactions.ThestatementSystem.out.println("WelcometoJava!")intheprograminListing1.1isastatementtodisplaythegreeting"WelcometoJava!"EverystatementinJavaendswithasemicolon(;).56BlocksApairofbracesinaprogramformsablockthatgroupscomponentsofaprogram.

57ClassesTheclassistheessentialJavaconstruct.Aclassisatemplateorblu