全國(guó)計(jì)算機(jī)等級(jí)考試網(wǎng)上報(bào)名系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn)

全國(guó)計(jì)算機(jī)等級(jí)考試網(wǎng)上報(bào)名系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn)全國(guó)計(jì)算機(jī)等級(jí)考試網(wǎng)上報(bào)名系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn)進(jìn)度安排1、已完成的工作安排：第1周確定畢業(yè)設(shè)計(jì)題目。第2周下達(dá)任務(wù)書；查閱、收集有關(guān)文獻(xiàn)資料。第3～4周撰寫并上交開題報(bào)告。2、待完成的工作安排：第5～8周根據(jù)安排進(jìn)行畢業(yè)實(shí)習(xí)及課題調(diào)研。第5周進(jìn)行系統(tǒng)需求分析和方案論證。第6周進(jìn)行系統(tǒng)總體設(shè)計(jì)。第7～8周進(jìn)行系統(tǒng)詳細(xì)設(shè)計(jì)。第9～11周進(jìn)行程序設(shè)計(jì)。第12～13周進(jìn)行系統(tǒng)測(cè)試；完成畢業(yè)論文的初稿。第14周系統(tǒng)驗(yàn)收；對(duì)畢業(yè)論文進(jìn)行修改并定稿；準(zhǔn)備論文答辯。六、主要參考文獻(xiàn)[1]鄧良松,陸麗娜.軟件工程.西安電子科技大學(xué)出版社,2001[2]王佑中，著,Web動(dòng)態(tài)技術(shù)入門,北京：機(jī)械工業(yè)出版社,2003[3]劉衛(wèi)宏.SQLServer2000實(shí)用教程.科學(xué)出版社，2003[4]劉廷等著.ASP.NET開發(fā)實(shí)例完剖析[M],北京：中國(guó)電力出版社[5]薩師煊,王珊.數(shù)據(jù)庫(kù)系統(tǒng)概論.高等教育出版社,2006[6]李閩溟，吳繼剛，周學(xué)明.WEB網(wǎng)站開發(fā)實(shí)例導(dǎo)航.人民郵電出版社,2003[7]王穎.敦促新理論的研究.哈爾濱工業(yè)大學(xué)碩士論文，1992[8]張小艷著.基于B/S模式的網(wǎng)上考試系統(tǒng)[J],工礦自動(dòng)化,2002年,04期第26-28頁(yè)[9]賈振華著.淺談網(wǎng)上考試系統(tǒng)中自動(dòng)抽題的實(shí)現(xiàn)[J],大眾科技,2003年,04期第106-107頁(yè)[10]李翠梅.SQLServer中數(shù)據(jù)完整性之表間關(guān)系[J].科技與經(jīng)濟(jì).2006年第24期107-108頁(yè)[11]張斌黃獻(xiàn)波.基于ASP.NET的用戶權(quán)限設(shè)計(jì)與實(shí)現(xiàn)[J].光盤技術(shù).2006年第3期28-30頁(yè)[12]宋陽(yáng).ASP.NET的網(wǎng)站科研成果管理系統(tǒng)的設(shè)計(jì)與實(shí)現(xiàn).長(zhǎng)春師范學(xué)院學(xué)報(bào)（自然科學(xué)版[J].第25卷第6期2006年12月53-55頁(yè)[13]夏陽(yáng)張強(qiáng)陳小林.基于ASP.NET的電子商務(wù)網(wǎng)站開發(fā)與設(shè)計(jì)[J].計(jì)算機(jī)工程與設(shè)計(jì).第25卷第11期2027-2029頁(yè)[14]王洪濤,劉文娛.深入剖析WEB編程技術(shù)及應(yīng)用實(shí)例.人民郵電出版社，2004[15]GrantPalmer著.康博譯.C#程序員參考手冊(cè)[M].清華大學(xué)出版社.2002年9月第1版.2002年9月第1次印刷[16]StevenMandel.MicrosoftSQLServer2005StoredProcedureProgramminginT-SQLand.NET[J].NetDeveloper'sJournalVol.5.No.5p.222007[17]J.R.McDnonell,D.Wagen.EvolvingRecurrentPercepptionsTimeModeling.IEEETrans.onNeuralNetwoks.1994[18]PeterVarhol.TheFutureofASP.NETHingesonWeb2.0[J].VisualStudioMagazineVol.17.No.1p.402007專業(yè)譯文原文：C#PrimerApracticalApproachChapter4.InterfaceInheritanceAninterfacespecifiesasetofabstractmethodsandproperties.Likeanabstractbaseclass,aninterfaceismadeconcretebyeachofitsderivedclasses.Unlikeanabstractbaseclass,aninterfacecannotprovideadefaultimplementationordefinestate,suchasaninstancedatamemberorconstant.Anabstractbaseclassprovidesacommoninterfaceforafamilyofrelatedtypes.Incomputergraphics,forexample,Lightmayserveasanabstractbaseclassforafamilyoflights.Usersarelikelytomanipulatethelightsinasceneindependentlyoftheactualtype—turningthemonoroff,repositioningthem,changingtheircolorandintensity,andsoon.ThedeliveryofaLighthierarchyincludestheabstractbaseclassandseveralcommonderivedinstances,suchasclassesrepresentingaspotlight,adirectionallight,andapointlight(thinkofthesun).Wecaneithermakeuseoftheseprebuiltinstancesorderiveanewinstance(s).Forexample,intheDisneyfilmDinosaurweintroducedaclasstorepresentabarn-doorlight.Aninterface,ontheotherhand,providesacommonserviceorcharacteristicforotherwiseunrelatedtypes.Forexample,anytypewishingtobethetargetoftheforeachstatementmustimplementtheIEnumerableinterface.Forexample,theArrayList,BindingManager,DataView,andBitArrayclassesareallderivedfromtheIEnumerableinterface,butotherwisetheyhavelittleincommon.Byconvention,interfacesunder.NETbeginwithacapitalIfollowedbyamnemonicidentifierwithacapitalizedfirstletter.ThisisacarryoverfromCOM-basedprogramming,whichhasinterfacessuchasIUnknownorIDirectDraw.Unlikeclasses,whichsupportsingleinheritanceonly,interfacessupportmultipleinheritance.TheSystem.Stringclass,forexample,isderivedfromfourinterfacesprovidedwithintheSystemnamespace:publicsealedclassString:IComparable,ICloneable,IConvertible,IEnumerable{...}AsC#programmers,wehavethreedifferentexperiencesofinterfaces:(1)asusersofconcreteinstancesofeithertheSystemoruser-introducedinterfaces,(2)asprovidersofanewclassimplementationofeithertheSystemoruser-introducedinterfaces,(3)asprovidersofanewinterfaceclass.Welookateachofthesethreeaspectsinthischapter.4.1ImplementingaSystemInterface:IComparableLet'sstartbyimplementingourownclassinstanceofapredefinedinterfacewithintheSystemnamespace.Themotivationalcontextisthefollowing:WeneedtosortanArrayListofstringsinascendingorderbythelengthofthestring.OK.Thatsoundssimpleenough.Sohowarewegoingtodothat?IfwelookatthepublicmethodsofArrayList,weseethatitprovidesanoverloadedpairofSort()memberfunctions:System.Collections.ArrayListSort:Overloaded.SortstheelementsintheArrayList,oraportionofit.Let'slookatthedocumentationforthetwodifferentmethodsandseewhichone,ifeither,fitsthebill.Here'stheonewithanemptyparameterlist:publicvirtualvoidSort()SortstheelementsintheentireArrayListusingtheIComparableimplementationofeachelement.JustbyitsnameweknowthatIComparableisaninterface.TheelementheldbyourArrayListisastring.TheStringclassimplementstheIComparableinterface.Theno-parameterSort()methodoftheArrayListusestheIComparableimplementationoftheStringclasstodeterminetheorderingoftwostringobjects.Thisimposesadictionaryorderonthewords—notanorderingbylength.Thisinstance,then,isnotofusetous.Okay.Maybethenextoverloadedinstanceisuseful:publicvirtualvoidSort(ICompareric)SortstheelementsintheentireArrayListusingthespecialcompareric.ThisinstanceprovidesuswithawaytooverridethedefaultorderingalgorithmassociatedwiththeStringclass.We'llcreateaspecialimplementationoftheIComparerinterfacethatsortsthestringsbylength.(Ifweweredefiningaclass,wewouldincludeanimplementationoftheIComparableinterfaceifwewantedtosupportsortingwithintheArrayListcontainer.)Howdowedothat?WhataretheIComparermethods,andwhatdotheydo?Notonlydowehavetoprovideadefinitionofeveryinterfacemember,butwemustimplementthedocumentedbehaviorofeachmemberifwewantourimplementationtotransparentlymeldwiththeotherimplementationsofthatinterface.Inaddition,weneedtothrowthesameexceptionsunderthesameabnormalconditions.Thecompilercannotenforcethis.Recognizingandthrowingtheexceptionsareresponsibilitiesoftheinterfaceimplementation.Itturnsoutthereisonlyonemethodtoimplement.Phew!Notonlythat,buttheimplementationseemsdoable:intCompare(objectx,objecty);Comparestwoobjectsandreturnsavalueindicatingwhetheroneislessthan(negativenumber),equalto(zero),orgreaterthan(positivenumber)theother.Whataboutanyexceptionsthemethodcanthrow?Againwehavetolookatthedocumentation.Asitturnsout,thereisjustone,anditalsoseemsdoable:ArgumentExceptionNeitherxnoryimplementstheIComparableinterface.-or-xandyareofdifferenttypesandneitheronecanhandlecomparisonswiththeother.ThismeansthatourimplementationoftheIComparerinterfacerequiresonlyonemethod:Compare().ItshouldthrowanArgumentExceptionifoneorbothofthetwoargumentsareinvalid;inourcase,thatsimplymeansthatthetwoargumentsarenotbothstrings.Let'scalltheclassStringLengthComparer:publicsealedclassStringLengthComparer:IComparer{//firstobligation:theCompare()methodpublicintCompare(objectx,objecty){...}}OurCompare()instancemustdefinetwoparametersoftypeobject,eventhoughourimplementationisinterestedinonlytwoparametersofthestringtype.ThisisnecessarybecauseCompare()isimplicitlyavirtualfunction(asareallinterfacememberfunctions),andthereforethesignatureoftheoverridinginstancemustexactlymatchthesignatureoftheinheritedmethod.Thisissomethingofaninconvenience.ItmeanswehavetocheckwithinCompare()thattheargumentsarebothoftypestring.Ifwewereabletoexplicitlydeclarethemastypestring,thecompilerwouldenforcethattyperequirementautomatically.We'llseehowtogetaroundthat—atleastpartially—inSection4.4.TheonlythingleftnowistheimplementationofCompare().Wecanbreakthatdownintotwoprimarysteps.Firstwemustconfirmthevalidityofthetwoarguments.Thatdone,wemustcomparethelengths.Wehavetwoparametersoftypeobject,andwemustconfirmthattheyarereallyinstancesoftypestring.Onestrategyistousetheisoperator:if((!(xisstring))||(!(yisstring)))thrownewArgumentException("somediremessage");//OK:argumentsarevalid;//let'scastthemtostringobjectsstringxs=(string)x;stringys=(string)y;Alternatively,wecanallowtheasoperatortodothedowncasting.Wethrowanexceptionifeitherxsorysissettonull:stringxs=xasstring;stringys=yasstring;if(xs==null||ys==null)thrownewArgumentException("somediremessage");That'sreallytheonlytrickypart.Hereisthelengthcomparison:intret_val=1;if(xs.Length<ys.Length)ret_val=-1;elseif(xs.Length==ys.Length)ret_val=0;returnret_val;Sowe'veimplementedourfirstconcreteinstanceofaninterfaceclass.HereishowwemightinvokeSort():ArrayListstringList=newArrayList();//fillitupstringList.Sort(newStringLengthComparer());4.2AccessinganExistingInterfaceInthissectionweimplementagenericbinarytreethatholdsnodevaluesofanytype.Asyouknowbynow,thewaywedothatinC#istodeclarethenodetobeoftypeobject.Asanadditionalwrinkle,anodevalueisinsertedonlyoncewithinatree.Ifitoccursanothertime,weincrementanoccurrencecount.ThisgivesusthechancetolookattheIComparableinterface.ThenodeclassiscalledTreeNode:publicsealedclassTreeNode{privateintm_occurs;privateobjectm_nval;privateTreeNodem_lchild,m_rchild;//...}Forourtreewe'llimplementseveralpoliciesthatprovideopportunitiesforexercisingsomeoftheinterfacesdefinedwithinthe.NETframework.Forexample,wewanttofixthetypeofthetreeafterinsertingthefirstelement.ThetreeclassiscalledBinaryTree:publicclassBinaryTree{publicdelegatevoidAction(refTreeNodenode);privateTypem_elemType;privateTreeNodem_root;privateActionm_nodeAction;//...}WhentheusercreatesaBinaryTreeobject,wewantittobeabletoholdavalueofanytype.Wesupportthatcapabilitybyusingthetypeobject.Oncetheuserinsertsavalue,however,wewantalltheremainingvaluesinsertedinthattreetobeofthesametype.Theinsertionofafirstvaluelocksthetypeofthattree.Forexample,hereishowourtreemustbehave.Whenwecreateanewtree,itcanholdobjectsofanytype.Oncewehaveinsertedanelement,however,thetreecanstoreonlyotherelementsofthattype.Forexample,whenwewriteBinaryTreebt=newBinaryTree();btcanpotentiallystoreelementsofanytype.However,oncewewritebt.insert("Piglet");btbecomesabinarytreethatholdselementsoftypestring.Subsequentinsertionsofstringelements,suchasbt.insert("Eeyore");bt.insert("Roo");arefine.EachelementisinsertedwithinthetreeaccordingtotheorderingsupportedbytheIComparableinterface.Whatwewanttopreventisasubsequentattemptbytheuser,afterhavinginsertedanobjectofonetype,toinsertanobjectofadifferenttype.Forexample,iftheuserwritesbt.insert(1024);wewanttorecognizeandflagthatthetypebeinginsertedisdifferentfromthetypetowhichwe'vepreviouslyboundourtree.Todothis,we'llthrowanexception.We'llmakenofurtherconstraintsonobjectsinorderforthemtobeacceptedastreenodevalues.OnlytypesthatimplementtheIComparableinterfaceareaccepted.Why?Becauseeachelementispassedtousthroughtheobjectparameter,sowehavelostallcompile-timetypeinformation.Theinterfaceprovidesanorderingservicethatistypeindependent—forexample,privateIComparableconfirm_comparable(objectelem){IComparableic=elemasIComparable;if(ic==null){stringmsg="ElementtypemustsupportIComparable--"+elem.GetType().Name+"doesnotcurrentlydoso!";thrownewArgumentException(msg);}returnic;}Hereishowwemightinvokeconfirm_comparable():publicvoidinsert(objectelem){//ifthisisthefirstelementif(m_root==null){confirm_comparable(elem);m_elemType=elem.GetType();m_root=newTreeNode(elem);}else{confirm_type(elem);m_root.insert_value(elem);}}insert()checkstheelement'ssuitabilityonlywiththefirstinsertionofanobjectofthattype.Subsequently,itsimplyconfirmsthatthenewobjectisofthesametypeastheinitialobject.Ifitis,weinserttheelementwithinthetree,asshownhere:publicvoidinsert_value(objectval){//assumptionisthatBinaryTreehasconfirmedthis...IComparableic=valasIComparable;//OK:zeromeansthetwoobjectsareequalif(ic.CompareTo(m_nval)==0){m_occurs++;return;}//OK:lessthan;insertwithinleftsubtreeif(ic.CompareTo(m_nval)<0){if(m_lchild==null)m_lchild=newTreeNode(val);elsem_lchild.insert_value(val);}else{//insertwithinrightsubtreeif(m_rchild==null)m_rchild=newBTreeNode(val);elsem_rchild.insert_value(val);}}Whenwemanipulateanobject'sactualtype,wecanprettymuchignorewhateverinterfacesthattypeimplements.Whenwemanipulateanentityoftypeobject,however,thediscoveryanduseofaninterfacebecomescriticalbecauseallcompiletimetypeinformationislost.(Alternatively,wecanquerytheobjectatruntimeastoitsactualtype.WelookattypereflectioninSection8.2.)4.3DefininganInterfaceInSection4.1weimplementedanewinstanceofanexistinginterface.InSection4.2wesimplydiscoveredandusedtheinterfaceassociatedwithagiventype.Inthissectionweintroduceaninterfacedefinition.Thisinterfacesupportsthegenerationanddisplayofsequencesofnumbersbasedonauniquealgorithm.Hereisthegeneralsetofoperationswewishtosupport(twomethods,aproperty,andanindexer):*GenerateSequence(),whichgeneratestheuniquesequenceofelements*Display(),whichoutputstheelements*Length,whichreturnsacountofthenumberofelements*Indexer,whichallowstheusertoaccessaspecificelementAninterfacedefinitionbeginswiththekeywordinterfacefollowedbyaname.Recallthatin.NET,interfacesbyconventionbeginwithacapitalI.Thenamefollows,beginningwithacapitalletter,althoughthisconventionisnotenforcedbythecompiler.We'llcallourinterfaceINumericSequence:publicinterfaceINumericSequence{}Yes,itislegaltodefineanemptyinterface,sothisrepresentsacompleteinterfacedefinition.Themembersthataninterfaceispermittedtodefineareasubsetofthosepermittedforaclass.Aninterfacecandeclareonlymethods,properties,indexers,andeventsasmembers—forexample,publicinterfaceINumericSequence{//amethodboolgenerate_sequence(intposition);//asetofoverloadedmethodsvoiddisplay();voiddisplay(intfirst);voiddisplay(intfirst,intlast);//apropertyintLength{get;}//aone-dimensionalindexerintthis[intposition]{get;}}Allmembersofaninterfaceareimplicitlyabstract.Wecannotprovideadefaultimplementation,howevertrivial.Inaddition,themembersoftheinterfaceareimplicitlypublic.Wecannotmodifyamemberwitheithertheabstractorthepublickeyword.Aninterfacecannotdefineinstancedatamembers.Norcanitdefineeitheraconstructororadestructor.(Withoutstatemembers,neitherisrequired.)Inaddition,aninterfacecannotdeclarestaticmembers.Becauseaconstmemberisimplicitlystatic,constmembersarenotallowed,andneitherareoperatorsnor,notsurprisingly,astaticconstructor.Aninterfacecaninheritfromanotherinterface:publicinterfaceINumericSequence:ICollection{...}orfrommultipleinterfaces:publicinterfaceINumericSequence:ICollection,ICloneable{...}butaninterfacecannotexplicitlyinheritfromaclassorstruct.Allinterfaces,however,implicitlyinheritfromtherootObjectclass.4.3.1ImplementingOurInterface:ProofofConceptOncewehavedefinedourinterface,howcanwetellifitisanygood?Typically,inadditiontodefiningtheinterface,wedeliveratleastoneimplementation—asakindofproofofconceptorsanitychecktoconfirmtheviabilityoftheinterface.Let'sprovideaFibonacciimplementationtotestourinterface.ThefirsttwoelementsoftheFibonaccisequenceareboth1.Addingthetwopreviouselementsgenerateseachsubsequentelement.Forexample,thefirsteightFibonaccielementsare1,1,2,3,5,8,13,21.Sowhatdowedofirst?Aninterfaceisimplementedbyeitherclassorstructinheritance.Astructisn'tappropriateinthiscase:Wedon'texpecttobecreatingandmanipulatinglotsofFibonacciobjectsintime-criticalportionsoftheapplication.We'lldeclareFibonacciasaclassthen.Becausewedonotexpectittobesubsequentlyderivedfrom,we'lldeclareittobesealedaswell:publicsealedclassFibonacci:INumericSequence{}Thisemptydefinition,however,isillegal.Aclassinheritingfromaninterfacemustprovideanimplementationofeveryinterfacemember.Leavingoutevenonememberresultsinacompile-timeerror.(Theexceptionisanycaseinwhichtheclassimplementingtheinterfaceisabstract.Itcanthendeclareoneormoreoftheinterfacememberfunctionsabstract.ThisisillustratedinSection4.5.)Beforewecanimplementtheinterfacemembers,wemustdeterminethestateinformationnecessarytosupportthesequenceabstraction.Inthiscasewe'llneedanarraytoholdthesequenceelements,andtwoadditionalmemberstoholdthesizeandcapacityofthearray.Becausetheelementsofthesequenceareinvariant,weneedonlyasinglearray.We'lldeclarethearrayanditstwosupportingmembersasstatic.Theimplementationofaninterfacehastwomainelements:(1)providingtheunderlyinginfrastructure,ifany,tosupporttheabstraction,and(2)providingadefinitionforeachmemberoftheinterface,includingthemembersofallinheritedbaseinterfaces.HereistheskeletonofaFibonacciclassdesign:publicsealedclassFibonacci:INumericSequence{//infrastructuretosupportsequenceabstractionprivatestaticint[]m_elements;privatestaticshortm_count;privatestaticshortm_capacity=128;//Fibonacci-specificmethods://allforinfrastructuresupportsstaticFibonacci(){...}privatevoidcheck_pos(intpos){...}privatevoidgrow_capacity(){...}//INumericSequenceinheritedmemberspublicboolgenerate_sequence(intpos){...}publicvoiddisplay(){...}publicvoiddisplay(intfirst){...}publicvoiddisplay(intfirst,intlast){...}publicintLength{get{returnm_count;}}publicintthis[intposition]{...}}Theindexerhastoverifythevalidityoftheposition,ofcourse.I'vefactoredthatverificationintoaprivatememberfunction,check_pos().Ifthepositionisinvalid,anexceptionisthrown.Otherwisetheindexerreturnstheelement,decrementingthepositionbyone:publicintthis[intposition]{get{check_pos(position);returnm_elements[position-1];}}BecausearrayindexinginC#iszerobased—thatis,thefirstelementisretrievedwithanindexof0—wemustadjustthepositionspecifiedbytheuser.Whynotrequiretheusertomakethatadjustmentexplicitly?Whetherthat'sagooddecisionornotdependsontheperceivedsophisticationofourusers.Iftheyareothersoftwaredevelopers,requiringtheindextobezerobasedmightwellmakesense.Nonprogrammers,however,oftenfindthenotionofafirstelementbeingatpositionzeroveryunnatural.Byencapsulatingtheadjustmentwithintheclass,weshouldertheburdenandmakeusingourcodesaferandmorepleasantforourusers.Hereishowwemightexerciseourimplementation.FirstweprogramaninstancedirectlyasaFibonacciclassobject.NextweprogramitindirectlyasagenericINumericSequenceobject:publicstaticvoidMain(){//justsomemagicnumbers–usedaspositionsconstintpos1=8,pos2=47;//let'sdirectlyuseinterfacethroughclassobjectFibonaccifib=newFibonacci();//invokesindexer;//indexerinvokesgenerate_sequence(pos1);intelem=fib[pos1];intlength=fib.Length;stringmsg="ThelengthoftheINumericSequenceis";Console.WriteLine(msg+length.ToString());Console.WriteLine("Element{0}oftheFibonacciSequenceis{1}",pos1,elem);fib.display();//OK:let'snowuseinterfacegenericallyINumericSequenceins=fib;elem=ins[pos2];length=ins.Length;Console.WriteLine(msg+length.ToString());Console.WriteLine("Element{1}oftheFibonacciSequenceis{0}",elem,pos2);ins.display(44,47);}Asitturnsout,ourimplementationissomewhatflawed.(That'sthepointoftestingit.)Theproblemisself-evidentintheprogram'soutput:ThelengthoftheINumericSequenceis8Element8oftheFibonacciSequenceis21Elements1to8oftheFibonacciSequence:1123581321ThelengthoftheINumericSequenceis47Element47oftheFibonacciSequenceis-1323752223Elements44to47oftheFibonacciSequence:70140873311349031701836311903-1323752223What'sgoingonhere?Theprogramclaimsthattheforty-seventhelementoftheFibonaccisequenceis-1323752223.That'sreallynotright.Ifwelookatthedisplayofelements44through47,whathashappenedisprettyclear:Elements44to47oftheFibonacciSequence:70140873311349031701836311903-1323752223Wehavedeclaredm_elementstoholdelementsoftypeint.Unfortunatelytheforty-seventhFibonaccielementistoolargetobecontainedwithinanint.Thevalueoverflowedintothesignbit,sothevalueisincorrectlydisplayedasnegative.TobetterhandlelargeFibonaccivalues,weneedtoredefinem_elementsasatypeabletoholdlargervalues.Whattypeisthemostappropriate?Inadditiontotheintegraltypes,therearetwofloating-pointtypes(thesingle-precisionfloatandthedouble-precisiondouble)andthe28-digits-of-precisiondecimaltype.Let'sredeclarem_elementstobe,inturn,auint,aulong,adecimal,andadouble.Atposition50,onlytheulong,decimal,anddoubleareleftstanding:FibonacciElement#50:(int):-298632863FibonacciElement#50:(uint):3996334433FibonacciElement#50:(ulong):12586269025FibonacciElement#50:(decimal):12586269025FibonacciElement#50:(double):12586269025Atposition100,onlythedecimalanddoublearecapableofrepresentingthevalue.However,thedoublebeginstoloseprecisionbyrounding,whichisunacceptable.Onlythedecimalvaluesdonotroundoff.OurbestchoiceforrepresentingtheelementsoftheFibonaccisequenceisthusthedecimaltype:FibonacciElement#100:(ulong):37367171FibonacciElement#100:(decimal):354224848179261915075FibonacciElement#100:(double):3.54224848179262E20Still,however,thisisnotacompletesolution.Thedecimaltypereachesits28-digitlimitatposition139:FibonacciElement#139:(decimal):5583911FibonacciElement#139:(double):5.58406E28Whenweattempttocalculateposition140,thedecimalobjectoverflowsandthefollowingexceptionoccurs:System.OverflowException:ValueiseithertoolargeortoosmallforaDecimal.atSystem.Decimal.Add(System.Decimal,System.Decimal)atSystem.Decimal.op_Addition(System.Decimal,System.Decimal)atProject1.Fibonacci.version_decimal(Int32)atProject1.MainObj.Main()Wecanstoreanddisplayonlythefirst139FibonaccielementsusingthepredefinedC#arithmetictypes.Unlessweplantoimplementourownnumericclasssupportingverylargeintegralvalues,we'llneedtodefinealimittotheelementpositionausercanrequest.Becausethisholdstrueforanynumericsequence,weshouldaddthatlimitdefinitiontotheINumericSequenceinterface,asfollows:publicinterfaceINumericSequence{//thetwonewpropertiesintLength{get;}intMaxPosition{get;}//...restthesame...}publicsealedclassFibonacci:INumericSequence{//infrastructuretosupportsequenceabstractionprivatestaticint[]m_elements=newint[m_maxpos];privatestaticshortm_count;privateconstshortm_maxpos=128;publicintMaxPosition{get{returnm_maxpos;}}//...restthesame,exceptnolongerneedtogrowarray}ThismeansthatthereisaninfinitesetofFibonaccielementpositionsthatarelegitimatebutthatwecan'teasilysupportand,infact,havechosennottosupport.Inaddition,theusermightspecifyaninvalidposition—anyvaluelessthanorequaltozero.Howshouldwehandlethesetwoinvalidconditions?TheconventioninbothC#and.NETprogrammingistoreportallprogramanomaliesthroughtheraisingofanexception.Butwhichexceptionshoulditthrow?Shoulditthrowseparateexceptionsforaninvalidpositionandanunsupportedposition?Thereisnosinglerightanswer.Whoshoulddecide?Ifeachinterfaceimplementationisallowedtodecidewhetherandwhatexceptionstothrow,ifany,itbecomesnearlyimpossibletosafelyprogramtheinterfacegenerically.Forexample,towritethefollowingcodesequence:INumericSequenceins=oasINumericSequence;if(ins!=null)elem=ins[pos2];wemustknowthateveryimplementationoftheindexerreportsaninvalidpositioninexactlythesameway.Thismeansthattheinterfacedefinitionmustdecideunderwhatconditionsanexceptionmustbethrownandwhattheexceptionshouldbe.Unfortunately,wecandothatonlythroughdocumentation.ThereisnowaywithinC#todirectlyassociateamemberwithoneorasetofexceptionsitmaythrow.中文翻譯：4、接口繼承接口詳細(xì)說明了一組抽象的methods和properties。和abstractbaseclass一樣，接口依靠derivedclass將它塑造為具體實(shí)物而非抽象接口。和abstractbaseclass不同的是，接口不能提供缺省實(shí)現(xiàn)或是定義任何“狀態(tài)”，例如定義實(shí)體數(shù)據(jù)成員或常量。Abstractbaseclass為一整族相關(guān)型別提供了公共的接口。例如在計(jì)算機(jī)圖形學(xué)中，light可能作為一族發(fā)光體的abstractbaseclass，用戶可能在一組場(chǎng)景中以“與實(shí)際型別無關(guān)”的方式來操縱這些發(fā)光體，包括開啟或熄滅、調(diào)換位置、改變顏色和亮度、如此等等。整個(gè)Light體系包含abstractbaseclass、數(shù)個(gè)derivedclass也許代表聚光燈、定向燈、點(diǎn)光源（如太陽(yáng)等等）。我們可以利用這些預(yù)先建立好的classes?；驈闹性倥缮龅男碌腸l