计算机专业英语Unit-4-Programming-Language课件

Unit4ProgrammingLanguageSectionAProgrammingLanguageOverviewUnit4ProgrammingLanguageSec1BackgroundKnowledge背景知识计算机使用二进制语言，与人类使用的自然语言差别较大。为了让计算机能理解人类指令并正确去完成相应的任务需要借助于程序设计语言。程序语言的类别很多，在发展的历程上也经历了机器语言、汇编语言和高级语言等若干阶段。BackgroundKnowledge背景知识计算机使用Newwordsandusefulexpressionsgeneration/dʒenə'reiʃn/代，一代,产生,一世syntax/'sintæks/语法;有条理的排列;句法primitive/'prɪmɪtɪv/原始的,旧式的,上古的symbolic/sɪm'bɑlɪk/用符号的(用作符号的)neural/'njurəl/神经的;背侧的;神经中枢的imitate/'ɪmɪteɪt/模仿,冒充,效法switch/swɪtʃ/开关,转换;转换器;instruction/ɪn'strʌkʃn/指示;指令;用法说明Newwordsandusefulexpressio计算机专业英语Unit-4--Programming-Language课件计算机专业英语Unit-4--Programming-Language课件Newwordsandusefulexpressionstime-consuming费时间error-prone易错human-friendly友好的，人容易理解的scriptinglanguage脚本语言parentclass父类embeddedapplication嵌入式应用NewwordsandusefulexpressioContentsProgrammingLanguagesLevel2ProceduralOrientedProgramming4ObjectOrientedProgramming5ProgrammingParadigms3FiveGenerationofLanguages1ContentsProgrammingLanguagesFirstgenerationlanguages(1GL)Representtheveryearly,primitivecomputerlanguagesthatconsistedentirelyof1'sand0's-theactuallanguagethatthecomputerunderstands(machinelanguage).Firstgenerationlanguages(1GLSecondgenerationlanguages(2GL)Representastepupfromthefirstgenerationlanguages.Allowfortheuseofsymbolicnamesinsteadofjustnumbers.Secondgenerationlanguagesareknownasassemblylanguage.Codewritteninanassemblylanguageisconvertedintomachinelanguage(1GL).Secondgenerationlanguages(2GThirdgenerationlanguages(3GL)Wordsandcommandswerebeingused.Havesyntaxthatwasmucheasiertounderstand.includeC,C++,Java,andJavaScript,amongothers.Thirdgenerationlanguages(3GLThesyntaxusedin4GLisveryclosetohumanlanguage,animprovementfromthepreviousgenerationoflanguages.Typicallyusedtoaccessdatabases.Forexample,SQLandColdFusion.Fourthgenerationlanguages(4GL)Thesyntaxusedin4GLisveryDesignedtomakethecomputersolveagivenproblemwithouttheprogrammer.Usedforneuralnetworks(aformofartificialintelligencethatattemptstoimitatehowthehumanmindworks).ForExample:Prolog,OPS5,andMercury.Fifthgenerationlanguages(5GL)DesignedtomakethecomputerContentsProgrammingLanguagesLevel2ProceduralOrientedProgramming4ObjectOrientedProgramming5ProgrammingParadigms3FiveGenerationofLanguages1ContentsProgrammingLanguagesMachineLanguagemachinecodeinstructionswrittenasstringsofbinarydigits("bits").Theprogramminglanguageusedwasknownasbinarycode.Verydifficulttoworkwithduetotheabsenceofsymbolicinformation.MachineLanguagemachinecodeiAssemblyLanguageconsistedofthesetofmnemonicsneededtorepresentthecompleteinstructionsetusedbyaparticularCPU.Needtobeconvertedintomachinecodeinorderforthecomputertoexecutetheprograminstructions,andthiswascarriesoutbyaprogramcalledanassembler.Usedtodaymainlyforembeddedapplicationswherethereisarequirementforcompactandefficientcode,andwheretheamountofmemoryavailablemaybelimited.AssemblyLanguageconsistedofHigh-levellanguagesMorehuman-friendlyprogramminglanguagesbegantoemergethatallowedprogramstobewrittenusingEnglish-likecommands.Needtoconvertintomachinecodefirstforcomputertounderstand.High-levellanguagesMorehumanHigh-levelLanguagesExecutionTwoapproacheshavebeenusedtomaketheconversion.CompilerInterpreterconvertthehigh-levelcodeintomachinecodebeforetheprogramisloadedintothecomputer'sworkingmemory.converteachhigh-levelprograminstructionintomachinecodeatruntime.--executiontendstobeslower.High-levelLanguagesExecutionFORTRANOriginallydevelopedbyIBMin1954Goodatcarryingoutlargenumbersofcomplexcalculations,andisdesignedforuseinscientificandengineeringapplicationsInwidespreaduseandhascontinuedtoevolve.FORTRANOriginallydevelopedbyCOBOLCOBOL(CommonBusiness-OrientedLanguage)wasdesignedspecificallyforuseinbusiness,financialandadministrativeapplications.Approximately75%oftheworld’sbusinessistransactedonsystemswritteninCOBOL.DevelopmentandstandardizationofthelanguageisnowprimarilymanagedbytheInternationalStandardsOrganization(ISO).GraceHopperCOBOLCOBOL(CommonBusiness-OrOtherHigh-levelLanguagesSpecializedlanguagessuchasLISPandProlog(usedforapplicationsinvolvingartificialintelligence)Moregeneral-purposelanguagessuchasC,C++,Perl,JavaandVisualBasic.OtherHigh-levelLanguagesSpecContentsProgrammingLanguagesLevel2ProceduralOrientedProgramming4ObjectOrientedProgramming5ProgrammingParadigms3FiveGenerationofLanguages1ContentsProgrammingLanguagesProgrammingLanguagesCommonFeaturesInput-getdatafromaninputdevicesuchasadiskdriveorthekeyboardOutput-senddatatoanoutputdevicesuchasadiskdrive,visualdisplayunit,printerornetworkadapterArithmeticandlogic-performarithmeticoperationssuchasadditionandmultiplication,andlogicaloperationssuchascomparingthevalueoftwovariablesProgrammingLanguagesCommonFProgrammingLanguagesCommonFeatures-ContinueConditionalexecution-executeadifferentsetofprograminstructionsdependingonwhetheraspecifiedconditionistrueorfalseRepetition-executeasetofprograminstructionsrepeatedlyuntilsomeexitconditionevaluatestotrue(aconditionalloop)orforaspecifiednumberofiterations(acountingloop)ProgrammingLanguagesCommonFContentsProgrammingLanguagesLevel2ProceduralOrientedProgramming4ObjectOrientedProgramming5ProgrammingParadigms3FiveGenerationofLanguages1ContentsProgrammingLanguagesProceduralOrientedProgrammingAstructuredprogrammingparadigmbasedontheconceptofprocedurecalls.Theproceduresmaybesubroutines,methodsorfunctions,eachofwhichconsistsofacollectionofprogramstatementsthatareexecutedsequentiallyinordertocarryoutaspecifictask.ProceduralOrientedProgramminProceduralOrientedProgrammingMeritsMerits:Allowthesamecodetobere-usedrepeatedly.AvoidtheneedtousetheGOTOorJUMPstatementsfoundinunstructuredlanguages–avoid"spaghetticode".Suitedtomodularization.--reducetheoverallcomplexityofalargeapplicationbyorganizingtheapplicationscodeintorelatedfunctionalunits.ProceduralOrientedProgrammin26ContentsProgrammingLanguagesLevel2ProceduralOrientedProgramming4ObjectOrientedProgramming5ProgrammingParadigms3FiveGenerationofLanguages1ContentsProgrammingLanguagesObjectOrientedProgrammingAprogrammingparadigmthatusesobjectstomodeldataentities.Placestheemphasisonthedataratherthanonthefunctionscarriedoutbytheprogram.Objectsinteractwiththeapplication'susersandwitheachotherbysendingandreceivingmessages.(Themessagestowhichanobjectwillrespondaredefinedbytheobject'sinterface)ObjectOrientedProgrammingApObjectOrientedProgrammingComponentsClassvariables-belongtotheclassasawhole;thereisonlyonecopyofeachone.Instancevariablesorattributes-datathatbelongstoindividualobjects;everyobjecthasitsowncopyofeachone.Membervariables-referstoboththeclassandinstancevariablesthataredefinedbyaparticularclassObjectOrientedProgrammingCo29ObjectOrientedProgrammingComponents-ContinueClassmethods-belongtotheclassasawholeandhaveaccessonlytoclassvariablesandinputsfromtheprocedurecallInstancemethods-belongtoindividualobjects,andhaveaccesstoinstancevariablesforthespecificobjecttheyarecalledon,inputs,andclassvariablesObjectOrientedProgrammingCoEncapsulationAnobject'smembervariablesaredeclaredasprivate,andcanonlybeaccessedormodifiedbytheobject'sownmethods.Themethodsthemselvesareusuallydeclaredtobepublic,butthemannerinwhichtheymaybeinvokedisstrictlydefinedbytheobject'sinterface.Encapsulation:Theabilitytohideboththedataandthecodeimplementationofanobjectbehindtheobject'sinterface.EncapsulationAnobject'smembeInheritanceeachobjectisderivedfromatemplateobjectcalledaclass.Theclassdefinesthemembervariables,methods,andinterfaceforeachobjectcreatedfromit.subclasseswouldinheritthemembervariables,methodsandinterfaceoftheparentclass.Theabilityofasubclasstoinheritthec