C#語言參考手冊(cè)

C#LanguageReferenceOwners: AndersHejlsbergandScottWiltamuthFile: C#LanguageReference.docLastsaved: 1/2/2013Lastprinted:1/2/2013Version0.17b

NoticeThisdocumentationisanearlyreleaseofthefinaldocumentation,whichmaybechangedsubstantiallypriortofinalcommercialrelease,andisinformationofMicrosoftCorporation.Thisdocumentisprox'idedforinformationalpurposesonlyandMicrosoftmakesnowarranties,eitherexpressorimplied,inthisdocument.Informationinthisdocumentissubjecttochangewithoutnotice.Theentireriskoftheuseortheresultsoftheuseofthisdocumentremainswiththeuser.Complyingwithallapplicablecopyrightlawsistheresponsibilityoftheuser.Withoutlimitingtherightsundercopyright,nopartofthisdoaimentmaybereproduced,storedinorintroducedintoaretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,mechanical,photocopying,recording,orotherwise),orforanypurpose,withouttheexpresswrittenpermissionofMicrosoftCorporation.Microsoftmayhavepatents,patentapplications,trademarks,copyrights,orotherintellectualpropertyrightscoveringsubjectmatterinthisdocument.ExceptasexpresslyprovidedinanywrittenlicenseagreementfromMicrosoft,thefurnishingofthisdocumentdoesnotgiveyouanylicensetothesepatents,trademarks,copyrights,orotherintellectualproperty.Unpublishedwork.?1999-2000MicrosoftCorporation.Allrightsreserved.Microsoft,Windows,VisualBasic,andVisualC++areeitherregisteredtrademarksortrademarksofMicrosoftCorporationintheU.S.A,and/orothercountries.Other{productandcompanynamesmentionedhereinmaybethetrademarksoftheirrespectiveowners.TableofContentsTOC\o"1-5"\h\z\o"CurrentDocument"Introduction 1Hello,world 1Automaticmemorymanagement 2\o"CurrentDocument"Types 4Pr^lefinedtypes 5Arraytypes 7Typesystemunification 9Statements 10Statementlistsandblocks 10Labeledstatementsandgotostatements 10Localdeclarationsofconstantsandvariables 11Expressionstatements 11Theifstatement 11Theswitchstatement 12Thewhilestatement 12Thedostatement 13Thefbrstatement 13Theforeachstatement 13Thebreakstatementandthecontinuestatement 14Thereturnstatement 14Thethrowstatement 14Thetrystatement 14Thecheckedanduncheckedstatements 14TheIockstatement 14\o"CurrentDocument"Classes 14\o"CurrentDocument"Structs 15Interfaces 15Delegates 17Enums 18\o"CurrentDocument"Namespaces 18Properties 19Indexers 20Events 21Versioning 22\o"CurrentDocument"Lexicalstructure 27Phasesoftranslation 27Grammarnotation 27Pre-processing 28Pre-processingdeclarations 28#if,#elif,#clse,#endif 29Pre-processingcontrollines 30#line 31Pre-processingidentifiers 31Pre-processingexpressions 31Interactionwithwhitespace 32Lexicalanalysis 33

2.4.5Whitespace 33ProcessingofUnicodecharacterescapesequences 34Literals 362533Reafliterals 37Operatorsandpunctuators 40BasicconceptsMembers Namespacemembers Structmembers Enumerationmembers Classmembers Interfacemembers Arraymembers Delegatemembers Memberaccess Declaredaccessibility Accessibilitydomains Protectedaccess Accessibilityconstraints Signaturesandoverloading Scopes Namehiding Hidingthroughnesting..Hidingthroughinheritan)Namespaceandtypenames Fullyqualifiednames Types Valuetypes Defaultconstructors Structtypes Simpletypes Integraltypes Floatingpointtypes Thedecimaltype Thebooltype Enumerationtypes 4343434444444444444445474849505252535455Referencetypes 4343434444444444444445474849505252535455Classtypes Theobjecttype Thestringtype Interfacetypes Arraytypes Delegatetypes BoxingandunboxingBoxingconversions.UnboxingconversionsTOC\o"1-5"\h\z5.1.2Instancevariables 6Instancevariablesin structs 685.1.5Referenceparameters 68\o"CurrentDocument"6.Conversions 73Implicitconversions 73Identityconversion 73Implicitnumericconversions 73Implicitenumerationconversions 74Implicitreferenceconversions 74Implicitconstantexpressionconversions 74Explicitnumericconversions 75Explicitenumerationconversions 76Unboxingconversions 77User-definedexplicitconversions 77Standardimplicitconversions 77Standardexplicitconversions 786.4User-definedconversions 78Permitteduser-definedconversions 78Evaluationofuser-definedconversions 78User-definedimplicitconversions 79User-definedexplicitconversions 80817.Expressions

81Operatorprecedenceandassociativity * Unaryoperatoroverloadresolution * . Binaryoperatoroverloadresolution Candidateuser-definedoperators Una.rynumericpromotions7.3Memberlookup ■Applicablefunctionmember*."Betteriunetionmember -?????.?l..????.-FunctionmemberinvocationInvocationsonboxedinstances Virtualfunctionmemberlookup Interfacefunctionmemberlookup 7.5.2.Invariantmeaninginblocks Identicalsimplenamesandtypenames Indexeraccess 7.5.8Baseaccess 7.5.9Postfixincrementanddecrementoperators Objectcreationexpressions Arraycreationexpressions Delegatecreationexpressions .13checkedanduncheckedoperators5556667791122234444456688990001122G346788001-888888888.9999999999999999990-000000000000011115556667791122234444456688990001122G346788001-888888888.9999999999999999990-00000000000001111TOC\o"1-5"\h\zBitwisecomplementopemtor IllPrefixincrementanddecrementoperatois. . * * * 1127*6-8C*astexpressions ??<??.?+.?4.+??+.*+.*<?+<?.+?*+**+.+*.+4*+.**.+*.*4.+..*.113Multiplicationoperator 113Divisionoperator 114A?dditionoperator116Subtractionoperator 1177.9Relationaloperators 119Floating-pointcomparisonoperators 121Decimalcomparisonoperators 121Booleanequalityoperators.. 122Enumerationcomparisonoperators 122Referencetypeequalityoperators 122Stringequalityoperators 123Delegateequalityoperators.. 124Theisoperator 1241Integerlogicaloperators 1243Booleanlogicaloperators 125Conditionallogicaloperators... 125Booleanconditionallogicaloperators... 126User-definedconditionallogicaloperatoi's 126Conditionaloperator 127Assignmentoperators 127Constantexpressions 131\o"CurrentDocument"8.Statements 133Endpointsandreachability 133Statementlists 135Labeleustatemeni136DecIsrotionstatements 136Localvariabledeclarations 136Localconstantdeclarations 137Expressionstatements 1388?7SelectionstatementsI38Theifstatement 138Theswitchstatement 139

Iterationstatements Thewhilestatement,... Thedostatement Theforstatement Theforeachstatement... Jumpstatements Thebreakstatement Thecontinuestatement Thegotostatement Thereturnstatement Thethrowstatement Thetrystatement Thecheckedanduncheckedstatements Thelockstatement 9.Namespaces Compilationunits Namespacedeclarations Usingdirectives Usingaliasdiiectives UsingnamespacedirectivesNamespacemembers Typedeclarations…..………1Classmodifiers 1Abstractclasses 2Sealedclasses 2Classbasespecification 1Baseclasses 2Interfaceimplementations 3Classbody Inheritance Thenewmodifier Accessmodifiers Constituenttypes Staticandinstancemembers Nestedtypes 10.4.1Staticandinstancefields... 1Usingstaticreadonlyfieldsforconstants 2Versioningofconstantsandstaticreadonlyfields Fieldinitialization Variableinitializers Staticfieldinitialization 1421431431441451461421431431441451461461471471481491501521525556791155555566333444566778889901222334456666886866666666777777777710.5.2Staticmidinstsnccmethods.. 10.5.4Overridemethods. .……,.………*….………..……… 10.6.3Virtual,override,andabstractaccessors 10.9.3Conversionoperators * Instanceconstructors ConstructorinitializersInstancevariableinitializers Defaultconstructors Privateconstructors Optionalconstructorparameters Destructors 12.1Classloadingandinitialization 7677777878808082838485858586879l93969999ooooa)020203030505()60607081?!tructnioditier??.7677777878808082838485858586879l93969999ooooa)020203030505()6060708Arrays 215Arraytypes. 215TOC\o"1-5"\h\zArrayinitializers 217\o"CurrentDocument"Interfaces 21913.1.2Baseinterfaces 219Interfacemembers 2203.2.3Interfaceevents/ 22224Interfaceindexers 222Fullyqualifiedinterfacemembernames 224Interfaceimplementations 224Explicitinterfacememberimplementations 225Interfacemapping 227Interfaceimplementationinheritance 229Interfacere-implementation 231Abstractclassesandinterfaces 232\o"CurrentDocument"Enums 233Enumdeclarations 233Enumvaluesandoperations 236\o"CurrentDocument"Delegates 237Delegatemodifiers 237\o"CurrentDocument"Exceptions 239\o"CurrentDocument"Attributes 241TheAttributeUsageattribute 241Positionalandnamedparameters 24217.2Attributespecification 24317.3.2Run-timeretrievalofanattributeinstance 24517.4.1TheAttributeUsageattribute 246\o"CurrentDocument"Versioning 251\o"CurrentDocument"Unsafecode 253\o"CurrentDocument"Interoperability 255

Attnbutes TheCOMmportattribute TheCOMSourcelmerface'iattribute TheCOMVisibiIityattribute TheDispIdattribute TheDIIImportattribute TheGlobaIObjectattribute TheGuidattribute TheHasDefaultinterfaceattribute TheImportedFromCOMattribute The1nandOutattributes TheInterfaceTypeattribute TheIsCOMRegisterFunctionattribute TheMarshaIattribute TheNameattribute TheNoIDispatchattribute TheNonSeriaIizedattribute ThePredeclaredattribute TheReiurnsHResultattribute TheSerializableattribute TheSiructLayoutattribute TheSiructOffsetattribute TheTypeLibFuncattribute TheTypeLibTypeattribute TheTypeLibVarattribute 55556677777885555555555555222222222222299900005555667777788555555555555522222222222229990000 12日5556666666662222222222221.IntroductionC#isasimple,modem,objectoriented,andtype-safeprogramminglanguagederivedfromCandC++.C#(pronounced“Csharp")isfirmlyplantedintheCandC++familytreeoflanguages,andwillimmediatelybefamiliartoCandC++programmers.C#aimstocombinethehighproductivityofVisualBasicandtherawpowerofC++.C#isprovidedasapartofMicrosoftVisualStudio7.0.InadditiontoC#,VisualStudiosupportsVisualBasic,VisualC++,andthescriptinglanguagesVBScriptandJScript.AlloftheselanguagesprovideaccesstotheNextGenerationWindowsServices(NWGS)platform,whichincludesacommonexecutionengineandarichclasslibrary.The.NETsoftwaredevelopmentkitdefinesa"CommonLanguageSubset"(CLS),asortoflinguafrancathatensuresseamlessinteroperabilitybetweenCLS-compliantlanguagesandclasslibraries.ForC#developers,thismeansthateventhoughC#isanewlanguage,ithascompleteaccesstothesamerichclasslibrariesthatareusedbyseasonedtoolssuchasVisualBasicandVisualC++.C#itselfdoesnotincludeaclasslibrary.Therestofthischapterdescribestheessentialfeaturesofthelanguage.Whilelaterchaptersdescriberulesandexceptionsinadetail-orientedandsometimesmathematicalmanner,thischapterstrivesforclarityandbrevityattheexpenseofcompleteness.Theintentistoprovidethereaderwithanintroductiontothelanguagethatwillfacilitatethewritingofearlyprogramsandthereadingoflaterchapters.Hello,worldThecanonical4iHello,world"programcanbewritteninC#asfollows:usingSystem:classHeIIoIstaticvoidNfain(){Console.WiteLine("HeIIo,worId");ThedefaultHieextensionforC#programsis.cs,asinhello.es.Suchaprogramcanbecompiledwiththecommandlinedirectiveeschello.eswhichproducesanexecutableprogramnamedhello.exe.Theoutputoftheprogramis:Hei1o,worldCloseexaminationofthisprogramisilluminating:TheusingSystem;directivereferencesanamespacecalledSystemthatisprovidedbythe.NETruntime.ThisnamespacecontainstheConso1eclassreferredtointheMainmethod.Namespacesprovideahierarchicalmeansoforganizingtheelementsofaclasslibrary.A"using“directiveenablesunqualifieduseofthemembersofanamespace.The"Hello,world"programusesConsole.WiieLineasashorthandforSystem.Conso1e.UHteLine.Whatdotheseidentifiersdenote?Systemisanamespace,Consoleisaclassdefinedinthatnamespace,andW-iieLincisastaticmethoddefinedonthatclass.TheNfainfunctionisastaticmemberoftheclassHe11o.Functionsandvariablesarenotsupportedatthegloballevel;suchelementsarealwayscontainedwithintypedeclarations(e.g.,classandstructdeclarations).The"Hello,world“outputisproducedthroughtheuseofaclasslibrary.C#doesnotitselfprovideaclasslibrary.Instead,C#usesacommonclasslibrarythatisalsousedbyotherlanguagessuchasVisualBasicandVisualC++.ForCandC++developers,itisinterestingtonoteafewthingsthatdonotappearinthe“Hello,world''program.Theprogramdoesnotuseeither*'：:"or>"operators.The":："isnotanoperatorinC#atall,andthe>''operatorisusedinonlyasmallfractionofC#programs.C#programsuse"asaseparatorincompoundnamessuchasConso1e.MiteLine.Theprogramdoesnotcontainforwarddeclarations.ForwarddeclarationsarcneverneededinC#programs,asdeclarationorderisnotsignificant.Theprogramdoesnoiuse#incIudetoimportprogramtext.Dependenciesbetweenprogramsarehandledsymbolicallyratherthanwithprogramtext.Thissystemeliminatesbarriersbetweenprogramswrittenindifferentlanguages.Forexample,theConsoleclasscouldbewritteninC#orinsomeotherlanguage.AutomaticmemorymanagementManualmemory'managementrequiresdeveloperstomanagetheallocationandde-allocationofblocksofmemory.Manualmemorymanagementisbothtimeconsuminganddifficult.C#providesautomaticmemorymanagementsothatdevelopersarefreedfromthisburdensometask.Inthevastmajorityofcases,thisautomaticmemorymanagementincreasescodequalityandenhancesdeveloperproductivitywithoutnegativelyimpactingeitherexpressivenessorperformance.TheexampleusingSystem;pubIicclassStackIprivaleNodefirst=null;pubIicboolEmpty(get\return(first==null);publicobjeelPop(){if(first==null)thrownewException("Can1tPopfromanemptyStack.");objecttemp=first.Vaiue;first=first.Next;returntemp;publicvoidPush(objecto){first=newNode(o,first);classNode(publicNodeNext;publicobjectVaiue;publicNode(objeelvalue):this(vaIue,nulI){}publicNode(objectvalue,Nodenext){Next=next;Va1ue=value;}}}showsaStackclassimplementedasalinkedlistofNodeinstances.NodeinstancesarccreatedinthePushmethodandaregarbagecollectedwhennolongerneeded.ANodeinstancebecomeseligibleforgarbagecollectionwhenitisnolongerpossibleforanycodetoaccessit.Forinstance,whenanitemisremovedfromtheStack,theassociatedNodeinstancebecomeseligibleforgarbagecollection.TheexampleclassTestIstaticvoidNfain(){Stacks=newStack();for(inti=0;i<10;i++)s.Push(i);whiIe(!s.Empiy)Console.WileLine($.Pop());})showsatestprogramthatusestheStackclass.AStackiscreatedandinitializedwith10elements,andthenassignedthevaluenull.Oncethevariable$isassignednull,theStackandtheassociated10Nodeinstancesbecomeeligibleforgarbagecollection.Thegarbagecollectorispermittedtocleanupimmediately,butisnotrequiredtodoso.Fordeveloperswhoaregenerallycontentwithautomaticmemorymanagementbutsometimesneedfine-grainedcontrolorthatextraiotaofperformance,C#providestheabilitytowrite“unsafe"code.Suchcodecandealdirectlywithpointertypes,andfixobjectstotemporarilypreventthegarbagecollectorfrommovingthem.This"unsafe"codefeatureisinfact"safe"featurefromtheperspectiveofbothdevelopersandusers.Unsafecodemustbeclearlymarkedinthecodewiththemodifierunsafe,sodeveloperscan'tpossiblyuseunsafefeaturesaccidentally,andtheC#compilerandtheexecutionengineworktogethertoensurethatunsafecodecannotmasqueradeassafecode.TheexampleusingSystem;classTest{1unsafestaticvoid^iteLocations(by(e|]arr){fixed(byte*p_arr=arr)(byte*p_e1em=p.arr;for(inti=0;i<arr.Length;i++){bytevalue=*p_e1em;stringaddr=int.Format((int)p_eIem,"X");ConsoFe.5M,iteLine("arr[{0}]at0x{I}is(2}",i,addr,value);p_e1em++;)staticvoidMiin()|bytcI]arr=newbyte”(1,2,3,4,5};^iteLocations(arr);]}showsanunsafemethodnamed\M-iteLocationsthatfixesanarrayinstanceandusespointermanipulationtoiterateovertheelementsandwriteouttheindex,value,andlocationofeach.Onepossibleoutputoftheprogramis:TOC\o"1-5"\h\zarr[0] at 0x8E0360 i s Iarr[ I] at 0x8E0361 i s 2arr[2) at Ox8E0362 i s 3arr[3] at 0x8E0363 i s 4arr[4] at 0x8E0364 i s 5butofcoursetheexactmemorylocationsaresubjecttochange.1.3TypesC#supportstwomajorkindsoftypes:valuetypesandreferencetypes.Valuetypesincludesimpletypes(e.g.,char,int,andfIoat),enumtypes,andstructtypes.Referencetypesincludeclasstypes,interfacetypes,delegatetypes,andarraytypes.Valuetypesdifferfromreferencetypesinthatvariablesofthevaluetypesdirectlycontaintheirdata,whereasvariablesofthereferencetypesstorereferencestoobjects.Withreferencetypes,itispossiblefortwovariablestoreferencethesameobject,andthuspossibleforoperationsononevariabletoaffecttheobjectreferencedbytheothervariable.Withvaluetypes,thevariableseachhavetheirowncopyofthedata,anditisnotpossibleforoperationsononetoaffecttheother.TheexampleusingSystem;classClassIIpublicintValue=0;)classTestIstaticvoidNiiin(){intvail=0;intvaI2=vail;val2=123;ClassIrefl=newClass1();Class1ref2=ref1;ref2.Value=123;Console.teLine("Values:{0),{I|",vail,val2);Console.WiteLine("Refs:(0),{I}",ref1.Value,ref2,Value);)1showsthisdifference.TheoutputoftheprogramisValues:0,123Refs:123,123TheassignmenttothelocalvariablevalIdoesnotimpactthelocalvariableval2becausebothlocalvariablesareofavaluetype(int)andeachlocalvariableofavaluetypehasitsownstorage.Incontrast,theassignmentref2.Value=123:affectstheobjectthatbothreflandref2reference.Developerscandefinenewvaluetypesthroughenumandstructdeclarations,andcandefinenewreferencetypesviaclass,interface,anddelegatedeclarations.TheexampleusingSystem;pubIicenumColorIRed,Blue,Green}publicstructPointIpublicintx,y;}publicinterface(BaseIvoidF();IpublicinterfaceIDerived:1BaseIvoidG();}publicclassAIprotectedvoidH(){Console.WiteLinc("A.H");})publicclassB:A.1DerivedpublicvoidF()(Console.WiteLine("B.F,impIementationofIDerived.F");}publicvoidG()(Console.ViiteLine("B.G,imp1ementationofIDerived.G");}1publicdelegatevoidEmptyDeIegate();showsanexampleortwotoreachkindoftypedeclaration.Latersectionsdescribetypedeclarationsingreaterdetail.1.4PredefinedtypesC#providesasetofpredefinedtypes,mostofwhichwillbefamiliartoCandC++developers.Thepredefinedreferencetypesareobjeciandstring.Thetypeobjectistheultimatebasetypeofallothertypes.Thepredefinedvaluetypesincludesignedandunsignedintegraltypes,floatingpointtypes,andthetypesboolTchar,anddecimaI.Thesignedintegraltypesaresbyte,short,int,andIong;theunsignedintegraltypesarebyte,ushort.uint,andulong;andthefloatingpointtypesarefIoatanddouble.Thebooltypeisusedtorepresentbooleanvalues:valuesthatareeithertrueorfalse.Theinclusionofboolmakesiteasierfbrdeveloperstowriteself-documentingcode,andalsohelpseliminatetheall-too-commonC++codingerrorinwhichadevelopermistakenlyuseswhenshouldhavebeenused.InC#,theexamplenti=...;F(i)；if(i=0) //Bug:thetestshouldbe(i==0)G();isinvalidbecausetheexpressioni=0isoftypeint,andifstatementsrequireanexpressionoftypebool.

ThechartypeisusedtorepresentUnicodecharacters.Avariableoftypecharrepresentsasingle16-bitUnicodecharacter.Thedecimaltypeisappropriateforcalculationsinwhichroundingerrorsareunacceptable.Commonexamplesincludefinancialcalculationssuchastaxcomputationsandcurrencyconversions.Thedecimaltypeprovides28significantdigits.Thetablebelowlistseachofthepredefinedtypes,andprovidesexamplesofeach.TypeDescriptionExamplesobjectTheultimatebasetypeofallothertypesobjecto=newStack();stringStringtype;astringisasequenceofUnicodecharactersstrings="He11o";sbyte8-bitsignedintegraltypesbyteva1=12;short16-bitsignedintegraltypeshortva1=12;int32-bitsignedintegraltypeintva1=12;1ong64-bitsignedintegraltype1ongvail=12;longva12=34L;byte8-bitunsignedintegraltypebytevail=12;byteva12=34U;ushort16-bitunsignedintegraltypeushortval1=12;ushortval2=34U;uint32-bitunsignedintegraltypeuintvail=12;uintva12=34U;ulong64-bitunsignedintegraltypeu1ongvail=12;u1ongva12=34U;u1ongva13=56L:u1ongva14=78UL;floatSingle-precisionfloatingpointtypefloatvalue=1.23F;doub1eDouble-precisionfloatingpointtypedoub1evail=1.23doubleval2=4.56D:boolBooleantype;aboolvalueiseithertrueorfalseboolvalue=true;charCharactertype;acharvalueisaUnicodecharactercharvalue='h';decima1Precisedecimaltypewith28significantdigitsdecimalvalue=I.23MEachofthepredefinedtypesisshorthandforasystem-providedtype.Forexample,thekeywordiniisshorthandforastructnamedSysiem.Int32.Thetwonamescanbeusedinterchangeably,thoughitisconsideredgoodstyletousethekeywordratherthanthecompletesystemtypename.PredefinedvaluetypessuchasinIaretreatedspeciallyinafewwaysbutareforthemostparttreatedexactlylikeotherstructs.Thespecialtreatmentthatthesetypesreceiveincludesliteralsupportandefficientcodegeneration.C#'soperatoroverloadingfeatureenablesdeveloperstodefinetypesthatbehavelikethepredefinedvaluetypes.Forinstance,aDigi(structthatsupportsthesamemathematicaloperationsasthepredefinedintegraltypes,andthatconversiontoandfromthesetypes.usingSystem;structDigitI...IclassTestIstaticvoidTestInt(){inta=1;intb=2;intc=a+b;Console.\^iteLine(c);}staticvoidTestDigit(){Digita=(Digit)1;Digitb=(Digit)2;Digitc=a+b;Console.iteLine(c);)staticvoidMain(){TestInt();TestDigit();})1.5ArraytypesArraysinC#maybesingle-dimensionalormulti-dimensional.Both^rectangulaf'and"jagged“arraysaresupported.Single-dimensionalarraysarethemostcommontype,sothisisagoodstartingpoint.TheexampleusingSystem;classTestIstaticvoidMain(){nt[]arr=newint[5];for(inti=0;i<arr.Length;i++)arr[i|=i*i;for(inti=0;i<arr.Length;i++)Console.WiteLine("arr[{0}]={I}",i,arr[i]);createsasingle-dimensionalarrayofintvalues,initializesthearrayelements,andthenprintseachofthemout.Theprogramoutputis:arr[0]=0arr[4]=I6Thetypein11|usedinthepreviousexampleisanarraytype.Arraytypesarewrittenusinganon-array-typefollowedbyoneormorerankspecifiers.TheexampleclassTestIstaticvoidMsin(){int[]aI; // single-dimensionalarrayof intint[,]a2; 11 2-dimensionalarrayofintintj,,]a3; // 3*dimensionalarrayofintint[][]j2; // "jagged" array: arrayof(arrayof int)int[j[j[]j 3; // arrayof (array of(arrayofint))showsavarietyoflocalvariabledeclarationsthatusearraytypeswithintastheelementtype.Arraysarereferencetypes,andsothedeclarationofanarrayvariablemerelysetsasidespacefbrthereferencetothearray.Arrayinstancesareactuallycreatedviaarrayinitializersandarraycreationexpressions.TheexampleclassTestIstaticvoidMiin()(int[]aI=newint[](1,2,3);int[,]a2=newint[,]]{1,2.3},{4,5,6));int[,f]a3=newintjlO,20,301;nt[1[ ) j2= newi nt[31[J;j2[0j = new i nt[] ( 1, 2, 31;j2[11 = new int(l ( 1, 2, 3, 4, 5, 6);j2[2) = new i nt[] ( 1, 2, 3, 4, 5. 6,7,8,9);showsavarietyofarraycreationexpressions.Thevariablesa1,a2anda3denoterectangulararrays,andthevariablej2denotesajaggedarray.Itshouldbenosurprisethatthesetermsarebasedontheshapesofthearrays.Rectangulararraysalwayshavearectangularshape.Giventhelengthofeachdimensionofthearray,itsrectangularshapeisclear.Forexample,thelengthofa3'sthreedimensionsare10,20,and30respectively,anditiseasytoseethatthisarraycontains1Oa2O,3Oelements.Incontrast,thevariablej2denotesa“jagged“array,oran"arrayofarrays''.Specifically,j2denotesanarrayofanarrayofint,orasingle-dimensionalarrayoftypeint[].Eachoftheseint[]variablescanbeinitializedindividually,andthisallowsthearraytotakeonajaggedshape.Thee