Application Development with .NET 期末复习笔记

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1、Week21.Constants:mustbeinitialisedwhendeclaredCannotbeassignedatruntimeImplicitlystatic2.ValuetypesVSReferencetypesValuetypesReferencetypesAllocatedonthestackVariablesnotnullableSimpletype:bool,byte,int,long,char,floatStructtypeEnumtypeAllocatedontheheapVariablesarenullableClassInterfaceArrayD

2、elegateString???Stringisareferencetypes!Why?Console.WriteLine(typeof(string).IsClass);//trueIt'sareferencetype.ButbehavealittlelikevaluetypesItcan'tbeavalue-type,asvalue-typesneedaknownsizeforthestacketc.Asareference-type,thesizeofthe reference isknowninadvance,evenifthesizeofthestringisn't.It

3、 behaves likeyouexpectavalue-typetobehavebecauseitisimmutable;i.e.itdoesn't*changeoncecreated.Buttherearelotsofotherimmutablereference-types.Delegateinstances,forexample.*=exceptforinside StringBuilder,butyouneverseeitwhileitisdoingthis...Referencetypeexample:usingSystem;classSomeClass{publici

4、ntNumber=0;}classTest{staticvoidMain(){SomeClassref1=newSomeClass();SomeClassref2=ref1;ref2.Number=123;Console.WriteLine("Refs:{0},{1}",ref1.Number,ref2.Number);}}Valuetypeexample:Inti=10,j=10;Console.WriteLine("i={0},j={1}",i,j);1.C#usesLazyEvaluationIf((x!=0)&&1/x

5、otevaluatetherestoftheexpression,thewholeexpressionisflase.2.Inswitch,defaultisnotnecessary.1.ForeachloopForeach(typeidentifierinexpression)//loopForeach(intnumberinarrayOfInts)Console.WriteLine(number);2.Break:exitfromloopContinue:startnextiterationofloopReturn:exitmethodandreturntocallingmet

6、hodGoto:createbadlystructuredcode--DONOTUSE3.ArrayisanobjectratherthanvaluetypeItisanreferencetypeImplementsIEnumeableinterfacewecanuseforeachArraysize->array.length4.RectangularMulti-DimensionalarrayForexample:int[,]coords={{8,1},{12,16},{3,3}};int[,]myArray=newint[3,4];5.JaggedArray-Eachrowc

7、anhavedifferentnumberofcolumnsForexampleint[][]a=newint[3][];a[0]=newint[4];a[1]=newint[7];a[2]=newint[2];1.EnumerationsWeek31.Ifafieldisdeclaredreadonlyitsvaluecanonlybechangedwhenitisinitialisedorwithinaconstructor.2.Ifafieldisdeclare