服务器应用程序中英文对照外文翻译文献Word文档下载推荐.docx
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服务器应用程序中英文对照外文翻译文献Word文档下载推荐.docx
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ApplicationofPowerBuilderUserObjectsinDevelopingDistributedPrograms
0 Introduction
Theobject-orientedmethodsandtoolshavebeenrecommendedindevelopingsoftware.TheUserobjectofPowerBuildersimulatestheclassinobject-orientedconception.ItisoneofthemostflexileobjectstodeveloptheperformanceofPowerBuilder.ByusingPowerBuilder,thedevelopercandevelopthefunctionoftheprimaryobjectfunction,addnewuser-definedcomponentsandenhancethereuseofcode.Moreover,wecandevelopthecomponentbyC++toimprovethespeed-sensitiveparts,andinsertthemtothePowerBuilderprogram.
TherearetwokindsofPowerBuilderobjects:
oneofthemisthevisualobjects,theycanbeusedtocommunicatebetweenapplicationprogramandusers;
theotherkindofthemisthenonvisualobjects,ithasnovisualcomponent,andismainlyusedtoencapsulateandcompletethecertainkindsofbusinesslogic.
UserObjects——astheotherPowerBuilderobjects,containsomeofproperties,suchasevent、instancevariables、userobjectfunctionsetc.
Generally,anonvisualobjectrepresentstheoneclassinsystemanalysis.Wedon'
tintendtodiscusshowtodefineinstancevariablesandtowritethefunctionofuserobject,youcanreferthePowerBuilderdocuments.Usuallyweusenon-visualobjecttoperformthePowerBuilderdistributedapplication.
Distributedcomputingisanaturaloutgrowthofthedevelopmentofnetworkcomputersystemsthatusetheclient/serverarchitecture.Itallowsyoutogetthemostintheclient/serverarchitecture.TheconceptionofdistributedcomputingiscloselyconnectedwithRPC(remoteprocedurecall).RPCisthetechniquethattheclientprogramcancallprocesses(functions)oftheremoteComputer,andgettheprocessresult(functionreturnvalue).PowerBuildershieldmanydetailsofRPCandmakesiteasytodeveloptheserverandtheclientapplication.
1 TheApplicationofUserObjectsontheServer
Aremoteobjectisacustomclass(nonvisual)userobjectthatiscontainedinanapplicationlocatedonaremoteserver.Eachremoteobjectisacustomclassuser(nonvisual)objectthathasbeingmentionedinthepartofuserobjectsontheremoteserverapplication,theyprovideservicetotheclient.Remoteobjectscanbeinvokedacrossprocessboundariesoracrosscomputerboundaries.Thatis,aclientapplicationcaninvokearemoteobjectassociatedwithaseparateexecutableonthesamecomputeroronanothercomputerinanetwork.
Thekeystosuccessfuldistributedapplicationdevelopmentaretouseobject-orientedtechniqueandtoselectremoteobjectscarefully.PowerBuilder'
supportfordistributedcomputingisalogicalextensionofitsobject-orientedarchitecture.Forthisreason,aPowerBuilderapplicationthatusesobject-orientedtechniquescanbeconvertedtoadistributedapplicationwithaminimumofdifficulty.Whenyouarereadytobegindevelopingadistributedapplication,youneedtopackageyourbusinesslogicincustomclass(nonvisual)userobjects.Customclassuserobjectsprovidethefoundationforanydistributedapplication.Onceyouhavecreatedyournonvisualobjects,youcanmaketheadjustmentsrequiredforclientapplicationstoaccesstheseobjectsremotely.Anycustomclassuserobjectcanactasaremoteobjectinaserverapplication.However,notallnonvisualobjectsaregoodcandidatesfordistributedprocessing.Sincenetworkandserverperformancecandegradeiftoomanyobjectsaredeployedinremoteservers,youneedtobeselectiveaboutwhichobjectsyoudecidetomakeremote.
1.1 RemoteObjects
Thebasicbuildingblocksofaserverapplicationaretheremoteobjectsitcontains.Eachremoteobjectisacustomclass(nonvisual)userobjectthathasmethodsthatcanbeinvokedbyoneormoreclientapplications.Atypicalserverapplicationcontainsseveralnonvisualobjectsthatpackagebusinesslogicintoreusablecomponents.Sotheprimarytaskinbuildingaserverapplicationiswritingthemethodsforthenonvisualobjects.
1.1.1 Instancevariables
Theinstanceexistsinmemoryandhasvaluesassignedtoitspropertiesandvariables.
1.1.2 Passingbyreference
Youcanpassargumentstocomponentmethodsbyreference.However,thebehaviorissomewhatdifferentinadistributedapplicationthaninanondistributedapplication.Whenyoupassbyreference,thevariableisactuallycopiedtotheserverbeforethemethodisexecutedandthencopiedbackwhenthemethodcompletesexecution.Thisbehaviorisusuallytransparenttotheapplication;
butinsomesituationsitcanaffecttheoutcomeofprocessing.Forexample,supposeyoudefineamethodcalledincrement_valuesthattakestwoargumentscalledxandy,bothofwhicharepassedbyreference.Thescriptforthemethodincrementsxandyasshownbelow:
x
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