IntroToCSharpArticle40文档格式.docx

IntroToCSharpArticle40文档格式.docx

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C#Classes12

C#Structs16

C#Delegates&

Events17

GarbageCollection19

JavaProgrammerPointofView21

Objective-CProgrammerPointofView22

Summary23

Overview

C#（pronounced"

Csharp"

）isasimple,modern,object-oriented,andtype-safeprogramminglanguage.ItwillimmediatelybefamiliartoC/C++andJavaprogrammers.C#combinesthehighproductivityofRapidApplicationDevelopment（RAD）languagesandtherawpowerofC++.

ThisarticleintroducesC#,andcomparesittoothermodernobject-orientedlanguageslikeObjective-CandJava.

Objectives

Whenyou’vefinishedthearticle,youwillhave:

∙Ahigh-levelunderstandingoftheC#programminglanguage.

∙Ahigh-levelunderstandingofthe.NETframework.

∙AclearviewofthedifferencesandsimilaritiesintheimplementationofbasicscenariosinC#versusJavaandObjective-C.

IntroductiontoC#

C#isanobject-orientedlanguagethatenablesprogrammerstobuildquicklyawiderangeofapplicationsfortheMicrosoft®

.NETframework.ThegoalofC#andthe.NETframeworkistoshortendevelopmenttimebyfreeingthedeveloperfromworryingaboutseverallow-levelprogrammingtaskssuchasmemorymanagement,typesafetyissues,standardlibraries,arrayboundschecking,andsoon.Thisallowsdeveloperstospendthemajorityofdevelopmenttimeworkingontheirapplicationsandbusinesslogicinstead.

C#isasimple,modernobject-orientedandtype-safeprogramminglanguage.Letusseewhy.

Simple

BeingapartoftheMicrosoft.NETplatform,C#applicationsreceivesupportfromtheruntime,andtheyuseservicesprovidedbytheruntime.The.NETframeworkisamanagedenvironment:

theruntimemanagesmemoryallocation—thisfreesthedeveloperfromthattask.Programmersdonothavetodealwiththeburdenofmemorymanagementandeliminatingmemoryleaks.

C#supportsoperatoroverloading,similarlytoC++;

JavaandObjective-Cdonotsupportit.

Inheritance-relatedfeaturesareclearerandmoreprecisethaninC++:

Anabstractkeywordisusedinsteadofdeclaringpurevirtualfunctions.

Abstractclassesaredeclaredassuchdirectlybyusingtheabstractkeyword,notindirectlybylackofmethod/functionimplementation（"

purevirtualfunctions"

）.

Anabstractclassmaybecompletelyimplementedandyetbedeclaredabstractforarchitecturalreasons.

Anoverridekeywordisusedforoverridingavirtualmethod.

Newclassmembertypes,suchaspropertiesandindexers,areintroducedtosimplifycommontaskssuchaslistiterationandpropertygettingandsetting.

LessErrorProne

C#islesserror-pronethanC++duetothefollowingcharacteristics:

UnlikeC++,whereitispossibletodeclareanytypeofpointerandassignittoanyallocatedaddressorcastittoanyothertype,C#allowsonlytype-safecasting.Castingerrorsaredetectedateithercompiletimeoratruntime.However,ineithersituation,youwillnotmissanyerrors.

TheuseofGenerictypesallowstemplateclassestoremaintype-safeatcompiletime.Thisallowstheprogrammertodetecterrorsduringcompile,ratherthanatruntime.

RunningunderthemanagedCLR,boundscheckingisperformedformanagedarraysautomaticallywhileaccessingtheallocatedarraymemberobject.Thispreventsaccidentalmemorycorruption.

Modern

C#isdesignedtomeetmodernapplicationrequirements,aswellasintegratingmodernsoftwareconcepts:

C#,asa.NETlanguage,providesalargersetofbasictypes,includingforexampletheDecimaltypeusedtohandlefinancialapplicationscorrectly.

Knownconcepts,suchasenumeratedtypes,bitflags,first-classfunctionsandothers,becomefirst-classcitizentypeswitharichsetoffunctionalitiesthatrepresenttype-specificusagerequirements.

Itcontainsabuilt-inexception-handlingmechanism.

C#providesabuilt-ineventhandlerforsimplerhandlingofintegrated（forexample,GUIandWeb）applicationrequirements.

C#providesacompletereflectionmechanism,allowingobjectmetadatatobeexploredduringruntime.

ObjectOriented

C#supportsthethreepillarsofObject-OrientedProgramming:

Encapsulation

Aclasshastoolstohideitsimplementationdetailsandberesponsibleforitsobjects’state

Inheritance

The“isa”relationshipcanbedefinedbetweenclasses,enablingextensibilityandreusability

Polymorphism

Aprogramcanhandledifferenttypesofobjectsidentically,sharingthesamebase,havingpolymorphicbehavior,basedonspecificobjecttypes

EverythinginC#ispartofatype（forexample,class,interface,andstruct）.Thereareno“global”（non-member）functionsorvariables.

Everytypeinstance“isanobject.”Alltypesarederivedfromacommonbaseclass:

object.

WhiletheseconceptsareveryfamiliartoJavadevelopers,theyarefundamentallydifferent（andinsomecasesevencompletelynew）forC/C++/Objective-Cdevelopers.

AfewwordsaboutJava

JavaisaprogramminglanguageoriginallydevelopedbyJamesGoslingatSunMicrosystemsandreleasedin1995asacorecomponentofSunMicrosystems’Javaplatform.ThelanguagederivesmuchofitssyntaxfromCandC++buthasasimplerobjectmodelandfewerlow-levelfacilities.Javaapplicationstypicallyarecompiledtobytecode（classfile）thatcanrunonanyJavaVirtualMachine（JVM）regardlessofcomputerarchitecture.Javaisgeneral-purpose,concurrent,class-based,andobject-oriented.Itisdesignedspecificallytohaveasfewimplementationdependenciesaspossible.

AfewwordsaboutObjective-C

TheObjective-Clanguageisasimplecomputerlanguagedesignedtoenablesophisticatedobject-orientedprogramming.Objective-CisdefinedasasmallbutpowerfulsetofextensionstothestandardANSIClanguage.ItispossibletocompileanyCprogramwithanObjective-Ccompiler,andtofreelyincludeCcodewithinanObjective-Cclass.ItsadditionstoCaremostlyinspiredbySmalltalk,oneofthefirstobject-orientedprogramminglanguages.Allofthesyntaxfornon-object-orientedoperations（includingprimitivevariables,preprocessing,expressions,functiondeclarations,andfunctioncalls）isidenticaltoC,whilethesyntaxforobject-orientedfeaturesisanimplementationofSmalltalk-stylemessaging.Today,Objective-CisusedprimarilyonApple'

sMacOSXandiOS:

twoenvironmentsbasedontheOpenStepstandard,thoughnotcompliantwithit.Objective-CistheprimarylanguageusedforApple'

sCocoaAPI,anditwasoriginallythemainlanguageonNeXT'

sNeXTSTEPOS.

”

Historically,allarticlesaboutprogramminglanguagesstartwitha“HelloWorld!

”sample.Thisarticlewillfollowthistradition–hereisaC#versionofthispopularprogram:

C#

usingSystem;

classHelloApp

{

staticvoidMain（）

{

Console.WriteLine（"

HelloC#!

"

）;

}

}

Thiscodereferencesthe"

System"

namespace,whichprovidesthe"

Console"

class,declaresaclassandenclosed"

Main"

staticmethod,which,inturn,callstheConsoleclass’s"

WriteLine"

staticmethodtooutputastring.

Note:

RunningtheabovesampledirectlyunderWindowsPhone7willnotproduceanytangibleoutput,astheWindowsPhone7consoleisnotaccessible.Thecodeprovidedisonlyforcomparison.

LetusseethesameprogramwritteninJava:

Java

publicclassHelloWorld{

publicstaticvoidmain（String[]args）{

System.out.println（"

HelloJava!

AndnowinObjective-C:

Objective-C

#import<

stdio.h>

intmain（intargc,constchar*argv[]）{

printf（"

HelloObjective-C!

\n"

）;

return0;

Thefirstdifferenceisincodeorganization:

whilebothC#andJavahaveaclasswithonemethod,Objective-Chasjustamethod.

Theseconddifferenceliesinthesignatureofthemethod:

inC#,the“Main”methodmuststartwithcapital“M”,whileinJavaandObjective-C,itisnotarequirement.The“String[]”argumentforthe“Main”methodinC#isoptional.

Thethirddifferenceisinthe“Main”method’sreturntype:

inC#（andJava）,itreturnsvoidwhileinObjective-Citreturns“int”.InC#,theMainmethodcouldalsoreturnan“int”value.

Themoreweexaminethecodethemoredifferenceswewilldiscover.

DefiningaClass

Muchofobject-orientedprogrammingconsistsofwritingcodefornewobjects—definingnewclasses.TheclassdefinitionsinC#andJavaarefairlysimilar:

C#（andJava）

classFraction

publicintnumerator;

publicintdenominator;

publicvoidPrint（）

//C#

{0}/{1}"

numerator,denominator）;

//Java

//System.out.println（newPrintfFormat（"

%d/%d"

）.sprintf（numerator,denominator））;

InObjective-C,classesaredefinedintwoparts:

1.Aninterfacethatdeclaresthemethodsandinstancevariablesoftheclassandnamesitssuperclass

2.Animplementationthatactuallydefinestheclass（containsthecodethatimplementsitsmethods）

Typically,thesearesplitbetweentwofiles,thoughsometimesaclassdefinitionmayspanseveralfilesbyusingafeaturecalleda“category.”Thesameclass/interfacewritteninObjective-C:

Foundation/NSObject.h>

@interfaceFraction:

NSObject{

intnumerator;

intdenominator;

-（void）print;

-（void）setNumerator:

（int）n;

-（void）setDenominator:

（int）d;

-（int）numerator;

-（int）denominator;

@end

#import"

Fraction.h"

@implementationFraction

-（void）print{

%i/%i"

numerator,denominator）;

（int）n{

numerator=n;

（int）d{

denominator=d;

-（int）denominator{

returndenominat