46 Task 1 Introduction to Object-Oriented ProgrammingPHP動態(tài)網(wǎng)站開發(fā)項目教程課件

Project3OverwritetheMemberAdministrationSystemwiththePHPFrameworkLaravelTask1IntroductiontoObject-OrientedProgrammingSchoolofSoftware,ChengduPolytechnicLecturer:MuQichunIntroductiontoObject-OrientedProgrammingTheso-called"ProcedureOriented"or"PO"referstothatinordertoaccomplishonething,weneedtodivideitintoseveralstepsandperformtheminsequence.Inprogramming,itmeanstodividetheprojectrequirementsintoindividualmethodsandindividualdata,executetheminspecificordertofinallygetthetaskdone.Theso-called"ObjectOriented"or"OO"meansthatbeforewecouldcompleteatask,wecouldabstractconceptsofobjectfromthematter,addsomeattributesandmethodstotheobjectsandfinallyleteachobjectexecutetheirownmethods.Wehavefinishedtwoprojectsbefore.Weappliedtheprocedure-orientedprogrammingmethodologytowritetheprograms.Aswearewritingaprogram,thereisanothertypicalmethodologywecanapply,whichisobject-orientedprogramming.IntroductiontoObject-OrientedProgrammingLet'strytounderstandthetwodifferentprogrammingmethodologiesthroughanexample.Forinstance,ifwewanttodothelaundryusingawashingmachine,incaseofprocedure-orientedmethodology,wecangetitdoneinfollowingway:Putinclothes(method)>>>Pourinlaundrydetergent(method)>>>Addwater(method)>>>Wash(method)>>>Dry(method)Butifweapplytheobject-orientedmethodology,wecouldgetthelaundrydoneasfollows:First,abstracttwoobjects,"human"and"washingmachine."Next,addattributesandmethodstoobject"human",including"puttinginclothes"(method),"pouringinlaundrydetergent"(method)and"addingwater"(method).Addattributesandmethodstoobject"washingmachine",including"washing"(method)and"drying"(method).IntroductiontoObject-OrientedProgrammingNowwiththeobjects,attributesandmethods,wecaninvokerelevantcontentsandgetthetaskdone.Next,invokeinturn:Human.Puttinginclothes(method)>>>Human.Pouringinlaundrydetergent(method)>>>Human.Addingwater(method)>>>WashingMachine.Washing(method)>>>WashingMachine.Drying(method).IntroductiontoObject-OrientedProgrammingWecouldseethatwecanfavorablyfinishthetaskinbothways.Butwhatadvantagesanddisadvantagesdothetwomethodologiespossessrespectively?1Procedure-orientedprogrammingAdvantagesHighefficiency;intelligible;comprisedofenforceable,separatesteps;succinct.DisadvantagesHighdegreeofcoupling;poorextensibility;difficulttomaintain.2Object-orientedprogrammingAdvantagesLowdegreeofcoupling,easytobeusedrepeatedly;highextensibility;maintanence-friendly.Inaddition,object-orientedprogrammingalsohascharacteristicssuchasencapsulation,inheritanceandpolymorphismwhichenablingdesigningofsystemswithlowdegreeofcoupling,thusmakingthemmoreflexibleandeasiertomaintain.DisadvantagesLowerefficientcomparedwithprocedure-orientedprogramming.IntroductiontoObject-OrientedProgrammingGenerally,wecanapplytheprocedure-orientedprogrammingmethodologyforsomesimpleprojects.Butifwearedesigningcomplex,large-scalesystem,itissuggestedthatobject-orientedprogrammingmethodologyshouldbeapplied.ThreeCharacteristicsofObject-OrientedProgramming:EncapsulationNextlet'stakealookthethreecharacteristicsofobject-orientedprogramming:EncapsulationInheritancePolymorphism1EncapsulationTheso-calledencapsulationmeanstoencapsulateanobjectivematterinanabstractiveclass,andthenencapsulateitsattributesandmethods,definingthemonlyavailablewithintheclass.Andadditionalauthorizationwouldberequiredifexternalclassesormethodstrytoaccessattributesandmethodsencapsulatedwithinaclass.PHPprovidesthreeaccessmodifiers.Public:represents"global"and"shared",accessiblewithin,outsideaclassandinasubclass.Protected:represents"underprotection",onlyaccessibleinitsclassandthesubclass.Private:represents"private",accessibleonlywithinitsclass,neitheroutsidetheclassnorinthesubclass.Nextlet'slookatanexampleshowingtheencapsulationcharacteristicofobject-orientedmethodology.ThreeCharacteristicsofObject-OrientedProgramming:EncapsulationByrunningaboveprogram,wecannowunderstandtheencapsulationcharacteristicofobject-orientedprogramming.ThreeCharacteristicsofObject-OrientedProgramming:Inheritance2InheritanceTheso-calledinheritancereferstothatanewclassisallowedtobeproducedbyinheritingsomeorallofthecharacteristicsofanoriginalclass.Theoriginalclassiscalledparentclass,andthenewclassiscalledsubclass.Thesubclasscannotonlydirectlyinheritcommoncharacteristicsfromtheparentclass,butalsocreateitsownspecialcharacteristics.Wecantrytounderstandtheinheritancecharacteristicofobject-orientedprogrammingbyfollowingexample.ThreeCharacteristicsofObject-OrientedProgramming:Polymorphism3PolymorphismTheso-calledpolymorphismreferstothatanobjectcanoccurindifferentformsindifferentsituations(instantiated).Inotherwords,amethodinaparentclasscanbeoverwrittenandrewritteninitssubclasstofulfillotherdifferentrequirements.Theinstancebelowwillexplainthepolymorphismcharacteristicofobject-orientedprogramming.Wecouldseethatthereisamethodas"run"intheparentclass"bus."Thesubclass"car"hasinheritedfrom"bus",andthemethod"run"intheparentclassisoverwrittenandrewrittenini