java編程思想-畢業(yè)論文外文文獻(xiàn)翻譯

1、ThinkinginJavaAlthoughitisbasedonCJavaismeofa“pure”objectientedlanguage.BothCJavaarehybridlanguagesbutinJavathedesignersfeltthatthehybridizationwasnotasimptantasitwasinC.Ahybridlanguageallowsmultipleprogrammingstylesther

2、easonCishybridistosupptbackwardcompatibilitywiththeClanguage.BecauseCisasupersetoftheClanguageitincludesmanyofthatlanguage’sundesirablefeatureswhichcanmakesomeaspectsofCoverlycomplicated.TheJavalanguageassumesthatyouwant

3、todoonlyobjectientedprogramming.Thismeansthatbefeyoucanbeginyoumustshiftyourmindsetintoanobjectientedwld(unlessit’salreadythere).Thebenefitofthisinitialefftistheabilitytoprograminalanguagethatissimplertolearntousethanman

4、yotherOOPlanguages.Inthischapterwe’llseethebasiccomponentsofaJavaprogramwe’lllearnthateverythinginJavaisanobjectevenaJavaprogram.Eachprogramminglanguagehasitsownmeansofmanipulatingdata.Sometimestheprogrammermustbeconstan

5、tlyawareofwhattypeofmanipulationisgoingon.Areyoumanipulatingtheobjectdirectlyareyoudealingwithsomekindofindirectrepresentation(apointerinCC)thatmustbetreatedwithaspecialsyntaxAllthisissimplifiedinJava.Youtreateverythinga

6、sanobjectusingasingleconsistentsyntax.Althoughyoutreateverythingasanobjecttheidentifieryoumanipulateisactuallya“reference”toanobject.Youmightimaginethissceneasatelevision(theobject)withyourremotecontrol(thereference).Asl

7、ongasyou’reholdingthisreferenceyouhaveaconnectiontothetelevisionbutwhensomeonesays“changethechannel”“l(fā)owerthevolume”whatyou’remanipulatingisthereferencewhichinturnmodifiestheobject.Ifyouwanttomovearoundtheroomstillcontro

8、lthetelevisionyoutaketheremotereferencewithyounotthetelevision.Alsotheremotecontrolcanstonitsownwithnotelevision.Thatisjustbecauseyouhaveareferencedoesn’tmeanthere’snecessarilyanobjectconnectedtoit.Soifyouwanttoholdawdse

9、ntenceyoucreateaStringreference:Buthereyou’vecreatedonlythereferencenotanobject.Ifyoudecidedtosendamessagetosatthispointyou’llgetanerr(atruntime)becausesisn’tactuallyattachedtoanything(there’snotelevision).Asaferpractice

10、thenisalwaystoinitializeareferencewhenyoucreateit.HoweverthisusesaspecialJavafeature:stringscanbeinitializedwithquotedtext.NmallyyoumustuseamegeneraltypeofinitializationfobjectsJavaobjectsthemselvesareneverplacedinstatic

11、stage.Constantstage.Constantvaluesareoftenplaceddirectlyintheprogramcodewhichissafesincetheycanneverchange.Sometimesconstantsarecdonedoffbythemselvessothattheycanbeoptionallyplacedinreadonlymemy(ROM)inembeddedsystems.Non

12、RAMstage.Ifdatalivescompletelyoutsideaprogramitcanexistwhiletheprogramisnotrunningoutsidethecontroloftheprogram.Thetwoprimaryexamplesofthisarestreamedobjectsinwhichobjectsareturnedintostreamsofbytesgenerallytobesenttoano

13、thermachinepersistentobjectsinwhichtheobjectsareplacedondisksotheywillholdtheirstateevenwhentheprogramisterminated.Thetrickwiththesetypesofstageisturningtheobjectsintosomethingthatcanexistontheothermediumyetcanberesurrec

14、tedintoaregularRAMbasedobjectwhennecessary.JavaprovidessupptflightweightpersistencefutureversionsofJavamightprovidemecompletesolutionsfpersistenceOnegroupoftypeswhichyou’llusequiteofteninyourprogramminggetsspecialtreatme

15、nt.Youcanthinkoftheseas“primitive”types.Thereasonfthespecialtreatmentisthattocreateanobjectwithnew—especiallyasmallsimplevariable—isn’tveryefficientbecausenewplacesobjectsontheheap.FthesetypesJavafallsbackontheapproachta

16、kenbyCC.Thatisinsteadofcreatingthevariablebyusingnewan“automatic”variableiscreatedthatisnotareference.Thevariableholdsthevalueit’splacedonthestacksoit’smuchmeefficient.Javadeterminesthesizeofeachprimitivetype.Thesesizesd