j2me architecture and development environment

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1、Chapter3J2MEArchitectureandDevelopmentEnvironment35P:10CompCompRef8710-9ch03.vpThursday,February06,200311:40:12AM36J2ME:TheCompleteReferencesingJ2MEyoucandeveloppracticallyanyapplicationthatyoucanimagineforasmallcomputingdevice.Theonlylimitationsarethos

2、eposedbyavailableUresourcesonthesmallcomputingdeviceandyourskillsasaJ2MEprogrammer.Asmallcomputingdeviceisconstrainedbyitsresources,asyoulearnedpreviouslyinthisbook.TheserestrictionsareinflexibleandrequireyoutodesignyourJ2MEapplicationtoworkwithintheselimita

3、tions.Fortunately,J2MEtechnologyprovidestoolstobuildanindustrial-strengthJavaapplicationdesignedtorunonasmallcomputingdevice.WritingaJ2MEapplicationisnotunlikewritinganyJavaapplication.YouusethesamebasicprogrammingconstructsasusedinaJ2SEapplication.However,s

4、omeroutinescommonlyusedinaJ2SEapplicationmustbemodifiedorexcludedfromaJ2MEapplication.Inthischapter,you’lllearnmoreabouttheJ2MEarchitectureandhowconstraintsofthearchitecturerestricttheuseofroutinesthatyouprobablyemployinyourJ2SEapplications.Furthermore,you’l

5、lbeintroducedtotheJ2MEdevelopmentenvironmentandlearntechniquesforbuildingyourfirstJ2MEapplication.J2MEArchitectureThemodulardesignoftheJ2MEarchitectureenablesanapplicationtobescaledbasedonconstraintsofasmallcomputingdevice.J2MEarchitecturedoesn’treplacetheop

6、eratingsystemofasmallcomputingdevice.Instead,J2MEarchitectureconsistsoflayerslocatedabovethenativeoperatingsystem,collectivelyreferredtoastheConnectedLimitedDeviceConfiguration(CLDC).TheCLDC,whichisinstalledontopoftheoperatingsystem,formstherun-timeenvironme

7、ntforsmallcomputingdevices.TheJ2MEarchitecturecomprisesthreesoftwarelayers(Figure3-1).ThefirstlayeristheconfigurationlayerthatincludestheJavaVirtualMachine(JVM),whichdirectlyinteractswiththenativeoperatingsystem.Theconfigurationlayeralsohandlesinter-actionsb

8、etweentheprofileandtheJVM.Thesecondlayeristheprofilelayer,whichconsistsoftheminimumsetofapplicationprogramminginterfaces(APIs)forthesmallcomputingdevice.ThethirdlayeristheMobileInformationDevice