1.注释
‘ Single line only REM Single line only ‘’’ |
// Single line / Multiple line / /// /* |
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2.程序结构
Imports System Namespace Hello Class HelloWorld Overloads Shared Sub Main(ByVal args() As String) Dim name As String = “VB.NET” ‘See if an argument was passed from the command line If args.Length = 1 Then name = args(0) Console.WriteLine(“Hello, “ & name & “!”) End Sub End Class End Namespace |
using System; namespace Hello { public class HelloWorld { public static void Main(string[] args) { string name = “C#”; // See if an argument was passed from the command line if (args.Length == 1) name = args[0]; Console.WriteLine(“Hello, “ + name + “!”); } } } |
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3.数据类型
Value Types Boolean Byte, SByte Char Short, UShort, Integer, UInteger, Long, ULong Single, Double Decimal Date (alias of System.DateTime) structures enumerations Reference Types objects String arrays delegates Initializing Dim correct As Boolean = True Dim b As Byte = &H2A ‘hex or &O52 for octal Dim person As Object = Nothing Dim name As String = “Dwight” Dim grade As Char = “B”c Dim today As Date = #12/31/2010 12:15:00 PM# Dim amount As Decimal = 35.99@ Dim gpa As Single = 2.9! Dim pi As Double = 3.14159265 Dim lTotal As Long = 123456L Dim sTotal As Short = 123S Dim usTotal As UShort = 123US Dim uiTotal As UInteger = 123UI Dim ulTotal As ULong = 123UL Nullable Types Dim x? As Integer = Nothing Anonymous Types Dim stu = New With {.Name = “Sue”, .Gpa = 3.4} Dim stu2 = New With {Key .Name = “Bob”, .Gpa = 2.9} Implicitly Typed Local Variables Dim s = “Hello!” Dim nums = New Integer() {1, 2, 3} Dim hero = New SuperHero With {.Name = “Batman”} Type Information Dim x As Integer Console.WriteLine(x.GetType()) ‘ System.Int32 Console.WriteLine(GetType(Integer)) ‘ System.Int32 Console.WriteLine(TypeName(x)) ‘ Integer Dim c as New Circle isShape = TypeOf c Is Shape ‘ True if c is a Shape isSame = o1 Is o2 // True if o1 and o2 reference same object Type Conversion / Casting Dim d As Single = 3.5 Dim i As Integer = CType(d, Integer) ‘ set to 4 (Banker’s rounding) i = CInt(d) ‘ same result as CType i = Int(d) ‘ set to 3 (Int function truncates the decimal) Dim s As New Shape Dim c As Circle = TryCast(s, Circle) ‘ Returns Nothing if type cast fails c = DirectCast(s, Circle) ‘ Throws InvalidCastException if type cast fails |
Value Types bool byte, sbyte char short, ushort, int, uint, long, ulong float, double decimal DateTime (not a built-in C# type) structs enumerations Reference Types objects string arrays delegates Initializing bool correct = true; byte b = 0x2A; // hex object person = null; string name = “Dwight”; char grade = ‘B’; DateTime today = DateTime.Parse(“12/31/2010 12:15:00 PM”); decimal amount = 35.99m; float gpa = 2.9f; double pi = 3.14159265; // or 3.14159265D long lTotal = 123456L; short sTotal = 123; ushort usTotal = 123; uint uiTotal = 123; // or 123U ulong ulTotal = 123; // or 123UL Nullable Types int? x = null;Anonymous Types var stu = new {Name = “Sue”, Gpa = 3.5}; var stu2 = new {Name = “Bob”, Gpa = 2.9}; // no Key equivalent__Implicitly Typed Local Variables var s = “Hello!”; var nums = new int[] { 1, 2, 3 }; var hero = new SuperHero() { Name = “Batman” }; Type Information int x; Console.WriteLine(x.GetType()); // System.Int32 Console.WriteLine(typeof(int)); // System.Int32 Console.WriteLine(x.GetType().Name); // Int32 Circle c = new Circle(); isShape = c is Shape; // true if c is a Shape isSame = Object.ReferenceEquals(o1, o2) // true if o1 and o2 reference same object Type Conversion / Casting float d = 3.5f; i = Convert.ToInt32(d); // Set to 4 (rounds) int i = (int)d; // set to 3 (truncates decimal) Shape s = new Shape(); Circle c = s as Circle; // Returns null if type cast fails c = (Circle)s; // Throws InvalidCastException if type cast fails |
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4.常量定义
Const MAXSTUDENTS As Integer = 25‘ Can set to a const or var; may be initialized in a constructor_ ReadOnly MIN_DIAMETER As Single = 4.93 |
const int MAXSTUDENTS = 25;// Can set to a const or var; may be initialized in a constructor _ readonly float MIN_DIAMETER = 4.93f; |
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5.枚举定义
Enum Action Start [Stop] ‘ Stop is a reserved word Rewind Forward End Enum Enum Status Flunk = 50 Pass = 70 Excel = 90 End Enum Dim a As Action = Action.Stop If a <> Action.Start Then Console.WriteLine(a.ToString & “ is “ & a) ‘ “Stop is 1” Console.WriteLine(Status.Pass) ‘ 70 Console.WriteLine(Status.Pass.ToString) ‘ Pass_ |
enum Action {Start, Stop, Rewind, Forward}; enum Status {Flunk = 50, Pass = 70, Excel = 90}; Action a = Action.Stop; if (a != Action.Start) Console.WriteLine(a + “ is “ + (int) a); // “Stop is 1” Console.WriteLine((int) Status.Pass); // 70 Console.WriteLine(Status.Pass); // Pass |
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6.算术与逻辑操作
Comparison = < > <= >= <> Arithmetic + - / Mod \ (integer division) ^ (raise to a power) Assignment = += -= = /= \= ^= <<= >>= &= Bitwise And Or Xor Not << >> Logical AndAlso OrElse And Or Xor Not Note: AndAlso and OrElse perform short-circuit logical evaluations String Concatenation & |
Comparison == < > <= >= != Arithmetic + - / % (mod) / (integer division if both operands are ints) Math.Pow(x, y) Assignment = += -= = /= %= &= |= ^= <<= >>= ++ — Bitwise & | ^ ~ << >> Logical && || & | ^ ! Note: && and || perform short-circuit logical evaluations String Concatenation + |
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7.条件选择语法
‘Null-coalescing operator if called with 2 arguments x = If(y, 5) ‘ if y is not Nothing then x = y, else x = 5 ‘ Ternary/Conditional operator (IIf evaluates 2nd and 3rd expressions) greeting = If(age < 20, “What’s up?”, “Hello”) ‘ One line doesn’t require “End If” If age < 20 Then greeting = “What’s up?” If age < 20 Then greeting = “What’s up?” Else greeting = “Hello” ‘ Use : to put two commands on same line If x <> 100 AndAlso y < 5 Then x = 5 : y = 2 ‘ Preferred If x <> 100 AndAlso y < 5 Then x = 5 y = 2 End If ‘ Use to break up long single line or use implicit line break If whenYouHaveAReally < longLine And itNeedsToBeBrokenInto2 > Lines Then UseTheUnderscore(charToBreakItUp) ‘If x > 5 Then x = y ElseIf x = 5 OrElse y Mod 2 = 0 Then x += y ElseIf x < 10 Then x -= y Else x /= y End If Select Case color ‘ Must be a primitive data type Case “pink”, “red” r += 1 Case “blue” b += 1 Case “green” g += 1 Case Else other += 1 *End Select |
// Null-coalescing operator x = y ?? 5; // if y != null then x = y, else x = 5 // Ternary/Conditional operator greeting = age < 20 ? “What’s up?” : “Hello”; if (age < 20) greeting = “What’s up?”; else greeting = “Hello”; // Multiple statements must be enclosed in {} if (x != 100 && y < 5) { x = 5; y = 2; } No need for or : since ; is used to terminate each statement. if (x > 5) x = y; else if (x == 5 || y % 2 == 0) x += y; else if (x < 10) x -= y; *else x /= y; // Every case must end with break or goto case switch (color) { // Must be integer or string case “pink”: case “red”: r++; break; case “blue”: b++; break; case “green”: g++; break; default: other++; break; // break necessary on default_ } |
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8.循环语法
Pre-test Loops: | ||
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While c < 10 c += 1 End While |
Do Until c = 10 c += 1 Loop |
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Do While c < 10 c += 1 Loop |
For c = 2 To 10 Step 2 Console.WriteLine(c) Next |
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Post-test Loops: | ||
Do c += 1 Loop While c < 10 |
Do c += 1 Loop Until c = 10 |
‘ Array or collection looping
Dim names As String() = {“Fred”, “Sue”, “Barney”}
For Each s As String In names
Console.WriteLine(s)
Next
‘ Breaking out of loops
Dim i As Integer = 0
While (True)
If (i = 5) Then Exit While
i += 1
End While
‘ Continue to next iteration
For i = 0 To 4
If i < 4 Then Continue For
Console.WriteLine(i) ‘ Only prints 4
Next | Pre-test Loops: // no “until” keyword
while (c < 10)
c++;
for (c = 2; c <= 10; c += 2)
Console.WriteLine(c);
Post-test Loop:
do
c++;
while (c < 10);
// Array or collection looping
string[] names = {“Fred”, “Sue”, “Barney”};
foreach (string s in names)
Console.WriteLine(s);
// Breaking out of loops
int i = 0;
while (true) {
if (i == 5)
break;
i++;
}
// Continue to next iteration
for (i = 0; i <= 4; i++) {
if (i < 4)
continue;
Console.WriteLine(i); // Only prints 4
} |
| —- | —- |
9.数组定义
Dim nums() As Integer = {1, 2, 3} For i As Integer = 0 To nums.Length - 1 Console.WriteLine(nums(i)) Next ‘ 4 is the index of the last element, so it holds 5 elements Dim names(4) As String names(0) = “David” names(5) = “Bobby” ‘ Throws System.IndexOutOfRangeException ‘ Resize the array, keeping the existing values (Preserve is optional) ReDim Preserve names(6) Dim twoD(rows-1, cols-1) As Single twoD(2, 0) = 4.5 Dim jagged()() As Integer = { _ New Integer(4) {}, New Integer(1) {}, New Integer(2) {} } jagged(0)(4) = 5 |
int[] nums = {1, 2, 3}; for (int i = 0; i < nums.Length; i++) Console.WriteLine(nums[i]); // 5 is the size of the array string[] names = new string[5]; names[0] = “David”; names[5] = “Bobby”; // Throws System.IndexOutOfRangeException // Add two elements, keeping the existing values Array.Resize(ref names, 7); float[,] twoD = new float[rows, cols]; twoD[2,0] = 4.5f; int[][] jagged = new int[3][] { new int[5], new int[2], new int[3] }; jagged[0][4] = 5; |
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10.函数定义
‘ Pass by value (in, default), reference (in/out), and reference (out) Sub TestFunc(ByVal x As Integer, ByRef y As Integer, ByRef z As Integer) x += 1 y += 1 z = 5 End Sub Dim a = 1, b = 1, c As Integer ‘ c set to zero by default TestFunc(a, b, c) Console.WriteLine(“{0} {1} {2}”, a, b, c) ‘ 1 2 5 ‘ Accept variable number of arguments Function Sum(ByVal ParamArray nums As Integer()) As Integer Sum = 0 For Each i As Integer In nums Sum += i Next End Function ‘ Or use Return statement like C# Dim total As Integer = Sum(4, 3, 2, 1) ‘ returns 10 ‘ Optional parameters must be listed last and must have a default value Sub SayHello(ByVal name As String, Optional ByVal prefix As String = “”) Console.WriteLine(“Greetings, “ & prefix & “ “ & name) End Sub SayHello(“Strangelove”, “Dr.”) SayHello(“Mom”) |
// Pass by value (in, default), reference (in/out), and reference (out) void TestFunc(int x, ref int y, out int z) { x++; y++; z = 5; }int a = 1, b = 1, c; // c doesn’t need initializing TestFunc(a, ref b, out c); Console.WriteLine(“{0} {1} {2}”, a, b, c); // 1 2 5 // Accept variable number of arguments int Sum(params int[] nums) { int sum = 0; foreach (int i in nums) sum += i; return sum; } int total = Sum(4, 3, 2, 1); // returns 10 / C# 4.0 supports optional parameters. Previous versions required function overloading. / void SayHello(string name, string prefix = “”) { Console.WriteLine(“Greetings, “ + prefix + “ “ + name); } SayHello(“Strangelove”, “Dr.”); SayHello(“Mom”); |
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11.字符串操作
Special character constants (all also accessible from ControlChars class) vbCrLf, vbCr, vbLf, vbNewLine vbNullString vbTab vbBack vbFormFeed vbVerticalTab “” ‘ String concatenation (use & or +) Dim school As String = “Harding” & vbTab school = school & “University” ‘ school is “Harding (tab) University” school &= “University” ‘ Same thing (+= does the same) ‘ Chars Dim letter As Char = school.Chars(0) ‘ letter is H letter = “Z”c ‘ letter is Z letter = Convert.ToChar(65) ‘ letter is A letter = Chr(65) ‘ same thing _Dim word() As Char = school.ToCharArray ‘ word holds Harding ‘ No string literal operator Dim filename As String = “c:\temp\x.dat” ‘ String comparison Dim mascot As String = “Bisons” If (mascot = “Bisons”) Then ‘ true If (mascot.Equals(“Bisons”)) Then ‘ true If (mascot.ToUpper().Equals(“BISONS”)) Then ‘ true If (mascot.CompareTo(“Bisons”) = 0) Then ‘ true ‘ String matching with Like - Regex is more powerful If (“John 3:16” Like “Jo[Hh]? #:*”) Then ‘true ‘ Substring s = mascot.Substring(2, 3)) ‘ son s = Mid(“testing”, 2, 3) ‘ est ‘ Replacement s = mascot.Replace(“sons”, “nomial”)) ‘ s is “Binomial” ‘ Split Dim names As String = “Michael,Dwight,Jim,Pam” Dim parts() As String = names.Split(“,”.ToCharArray()) ‘ One name in each slot ‘ Date to string Dim dt As New DateTime(1973, 10, 12) Dim s As String = “My birthday: “ & dt.ToString(“MMM dd, yyyy”) ‘ Oct 12, 1973 ‘ Integer to String Dim x As Integer = 2 Dim y As String = x.ToString() ‘ y is “2” ‘ String to Integer Dim x As Integer = Convert.ToInt32(“-5”) ‘ x is -5 ‘ Mutable string Dim buffer As New System.Text.StringBuilder(“two “) buffer.Append(“three “) buffer.Insert(0, “one “) buffer.Replace(“two”, “TWO”) Console.WriteLine(buffer) ‘ Prints “one TWO three”_ |
Escape sequences \r // carriage-return \n // line-feed \t // tab \\ // backslash \“ // quote // String concatenation string school = “Harding\t”; school = school + “University”; // school is “Harding (tab) University” school += “University”; // Same thing // Chars char letter = school[0]; // letter is H letter = ‘Z’; // letter is Z letter = Convert.ToChar(65); // letter is A letter = (char)65; // same thing char[] word = school.ToCharArray(); // word holds Harding // String literal string filename = @“c:\temp\x.dat”; // Same as “c:\\temp\\x.dat” // String comparison string mascot = “Bisons”; if (mascot == “Bisons”) // true if (mascot.Equals(“Bisons”)) // true if (mascot.ToUpper().Equals(“BISONS”)) // true if (mascot.CompareTo(“Bisons”) == 0) // true // String matching - No Like equivalent, use Regex // Substring s = mascot.Substring(2, 3)) // son s = “testing”.Substring(1, 3); // est (no Mid) // Replacement s = mascot.Replace(“sons”, “nomial”)) // Binomial // Split string names = “Michael,Dwight,Jim,Pam”; string[] parts = names.Split(“,”.ToCharArray()); // One name in each slot // Date to string DateTime dt = new DateTime(1973, 10, 12); string s = dt.ToString(“MMM dd, yyyy”); // Oct 12, 1973 // int to string int x = 2; string y = x.ToString(); // y is “2”__// string to int int x = Convert.ToInt32(“-5”); // x is -5__// Mutable string System.Text.StringBuilder buffer = new System.Text.StringBuilder(“two “); buffer.Append(“three “); buffer.Insert(0, “one “); buffer.Replace(“two”, “TWO”); Console.WriteLine(buffer); // Prints “one TWO three” |
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12.正则表达式
Imports System.Text.RegularExpressions ‘ Match a string pattern Dim r As New Regex(“j[aeiou]h?. \d:“, RegexOptions.IgnoreCase Or RegexOptions.Compiled) If (r.Match(“John 3:16”).Success) Then ‘true Console.WriteLine(“Match”) End If ‘ Find and remember all matching patterns Dim s As String = “My number is 305-1881, not 305-1818.” Dim r As New Regex(“(\d+-\d+)”) Dim m As Match = r.Match(s) ‘ Matches 305-1881 and 305-1818 While m.Success Console.WriteLine(“Found number: “ & m.Groups(1).Value & “ at position “ & m.Groups(1).Index.ToString) m = m.NextMatch() End While ‘ Remeber multiple parts of matched pattern Dim r As New Regex(“(\d\d):(\d\d) (am|pm)”) Dim m As Match = r.Match(“We left at 03:15 pm.”) If m.Success Then Console.WriteLine(“Hour: “ & m.Groups(1).ToString) ‘ 03 Console.WriteLine(“Min: “ & m.Groups(2).ToString) ‘ 15 Console.WriteLine(“Ending: “ & m.Groups(3).ToString) ‘ pm End If ‘ Replace all occurrances of a pattern Dim r As New Regex(“h\w+?d”, RegexOptions.IgnoreCase) Dim s As String = r.Replace(“I heard this was HARD!”, “easy”) ‘ I easy this was easy! ‘ Replace matched patterns Dim s As String = Regex.Replace(“123 < 456”, “(\d+) . (\d+)”, “$2 > $1”) ‘ 456 > 123 ‘ Split a string based on a pattern Dim names As String = “Michael, Dwight, Jim, Pam” Dim r As New Regex(“,\s“) Dim parts() As String = r.Split(names) ‘ One name in each slot |
using System.Text.RegularExpressions; // Match a string pattern Regex r = new Regex(@”j[aeiou]h?. \d:“, RegexOptions.IgnoreCase | RegexOptions.Compiled); if (r.Match(“John 3:16”).Success) // true Console.WriteLine(“Match”); // Find and remember all matching patterns string s = “My number is 305-1881, not 305-1818.”; Regex r = new Regex(“(\\d+-\\d+)”); // Matches 305-1881 and 305-1818 for (Match m = r.Match(s); m.Success; m = m.NextMatch()) Console.WriteLine(“Found number: “ + m.Groups[1] + “ at position “ + m.Groups[1].Index); // Remeber multiple parts of matched pattern Regex r = new Regex(“@(\d\d):(\d\d) (am|pm)”); Match m = r.Match(“We left at 03:15 pm.”); if (m.Success) { Console.WriteLine(“Hour: “ + m.Groups[1]); // 03 Console.WriteLine(“Min: “ + m.Groups[2]); // 15 Console.WriteLine(“Ending: “ + m.Groups[3]); // pm } // Replace all occurrances of a pattern Regex r = new Regex(“h\\w+?d”, RegexOptions.IgnoreCase); string s = r.Replace(“I heard this was HARD!”, “easy”)); // I easy this was easy! // Replace matched patterns string s = Regex.Replace(“123 < 456”, @”(\d+) . (\d+)”, “$2 > $1”); // 456 > 123 // Split a string based on a pattern string names = “Michael, Dwight, Jim, Pam”; Regex r = new Regex(@”,\s“); string[] parts = r.Split(names); // One name in each slot |
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13.异常定义
‘ Throw an exception Dim ex As New Exception(“Something is really wrong.”) Throw ex ‘ Catch an exception Try y = 0 x = 10 / y Catch ex As Exception When y = 0 ‘ Argument and When is optional Console.WriteLine(ex.Message) Finally Beep() End Try ‘ Deprecated unstructured error handling On Error GoTo MyErrorHandler … MyErrorHandler: Console.WriteLine(Err.Description) |
// Throw an exception Exception up = new Exception(“Something is really wrong.”); throw up; // ha ha // Catch an exception try { y = 0; x = 10 / y; } catch (Exception ex) { // Argument is optional, no “When” keyword Console.WriteLine(ex.Message); } finally { Microsoft.VisualBasic.Interaction.Beep(); } |
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14.命名空间
Namespace Harding.Compsci.Graphics … End Namespace ‘ or Namespace Harding Namespace Compsci Namespace Graphics … End Namespace End Namespace End Namespace Imports Harding.Compsci.Graphics |
namespace Harding.Compsci.Graphics { … } // or namespace Harding { namespace Compsci { namespace Graphics { … } } } using Harding.Compsci.Graphics; |
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15.类与接口定义
Access Modifiers Public Private Friend Protected Protected Friend Class Modifiers MustInherit NotInheritable Method Modifiers MustOverride NotInheritable Shared Overridable ‘ All members are Shared Module ‘ Partial classes Partial Class Team … Protected name As String Public Overridable Sub DisplayName() Console.WriteLine(name) End Sub End Class ‘ Inheritance Class FootballTeam Inherits Team … Public Overrides Sub DisplayName() Console.WriteLine(“ “ + name + “ “) End Sub End Class ‘ Interface definition Interface IAlarmClock Sub Ring() Property TriggerDateTime() As DateTime End Interface ‘ Extending an interface Interface IAlarmClock Inherits IClock … End Interface ‘ Interface implementation Class WristWatch Implements IAlarmClock, ITimer Public Sub Ring() Implements IAlarmClock.Ring Console.WriteLine(“Wake up!”) End Sub Public Property TriggerDateTime As DateTime Implements IAlarmClock.TriggerDateTime … End Class |
Access Modifiers public private internal protected protected internal Class Modifiers abstract sealed static Method Modifiers abstract sealed static virtual No Module equivalent - just use static class // Partial classes partial class Team { … protected string name; public virtual void DislpayName() { Console.WriteLine(name); } // Inheritance class FootballTeam : Team { … public override void DislpayName() { Console.WriteLine(“ “ + name + “ “); } } // Interface definition interface IAlarmClock { void Ring(); DateTime CurrentDateTime { get; set; } } // Extending an interface interface IAlarmClock : IClock { … } // Interface implementation class WristWatch : IAlarmClock, ITimer { public void Ring() { Console.WriteLine(“Wake up!”); } public DateTime TriggerDateTime { get; set; } … } |
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16.构造与析构
Class SuperHero Inherits Person Private powerLevel As Integer Private name As String ‘ Default constructor Public Sub New() powerLevel = 0 name = “Super Bison” End Sub Public Sub New(ByVal powerLevel As Integer) Me.New(“Super Bison”) ‘ Call other constructor Me.powerLevel = powerLevel End Sub Public Sub New(ByVal name As String) MyBase.New(name) ‘ Call base classes’ constructor Me.name = name End Sub Shared Sub New() ‘ Shared constructor invoked before 1st instance is created End Sub Protected Overrides Sub Finalize() ‘ Destructor to free unmanaged resources MyBase.Finalize() End Sub End Class |
class SuperHero : Person { private int powerLevel; private string name; // Default constructor public SuperHero() { powerLevel = 0; name = “Super Bison”; } public SuperHero(int powerLevel) : this(“Super Bison”) { // Call other constructor this.powerLevel = powerLevel; } public SuperHero(string name) : base(name) { // Call base classes’ constructor this.name = name; } static SuperHero() { // Static constructor invoked before 1st instance is created } ~SuperHero() { // Destructor implicitly creates a Finalize method } } |
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17.对象的使用
Dim hero As SuperHero = New SuperHero ‘ or Dim hero As New SuperHero With hero .Name = “SpamMan” .PowerLevel = 3 End With hero.Defend(“Laura Jones”) hero.Rest() ‘ Calling Shared method ‘ or SuperHero.Rest() Dim hero2 As SuperHero = hero ‘ Both reference the same object hero2.Name = “WormWoman” Console.WriteLine(hero.Name) ‘ Prints WormWoman hero = Nothing ‘ Free the object If hero Is Nothing Then hero = New SuperHero Dim obj As Object = New SuperHero If TypeOf obj Is SuperHero Then Console.WriteLine(“Is a SuperHero object.”) ‘ Mark object for quick disposal Using reader As StreamReader = File.OpenText(“test.txt”) Dim line As String = reader.ReadLine() While Not line Is Nothing Console.WriteLine(line) line = reader.ReadLine() End While End Using |
SuperHero hero = new SuperHero(); // No “With” but can use object initializers SuperHero hero = new SuperHero() { Name = “SpamMan”, PowerLevel = 3 }; hero.Defend(“Laura Jones”); SuperHero.Rest(); // Calling static method SuperHero hero2 = hero; // Both reference the same object hero2.Name = “WormWoman”; Console.WriteLine(hero.Name); // Prints WormWoman hero = null ; // Free the object if (hero == null) hero = new SuperHero(); Object obj = new SuperHero(); if (obj is SuperHero) Console.WriteLine(“Is a SuperHero object.”);// Mark object for quick disposal using (StreamReader reader = File.OpenText(“test.txt”)) { string line; while ((line = reader.ReadLine()) != null) Console.WriteLine(line); } |
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18.结构定义
Structure Student Public name As String Public gpa As Single Public Sub New(ByVal name As String, ByVal gpa As Single) Me.name = name Me.gpa = gpa End Sub End Structure Dim stu As Student = New Student(“Bob”, 3.5) Dim stu2 As Student = stu stu2.name = “Sue” Console.WriteLine(stu.name) ‘ Prints Bob Console.WriteLine(stu2.name) ‘ Prints Sue |
struct Student { public string name; public float gpa; public Student(string name, float gpa) { this.name = name; this.gpa = gpa; } } Student stu = new Student(“Bob”, 3.5f); Student stu2 = stu; stu2.name = “Sue”; Console.WriteLine(stu.name); // Prints Bob Console.WriteLine(stu2.name); // Prints Sue |
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19.属性的定义
Auto-implemented properties are new to VB10 Public Property Name As String Public Property Size As Integer = -1 ‘ Default value, Get and Set both Public ‘ Traditional property implementation Private mName As String Public Property Name() As String Get Return mName End Get Set(ByVal value As String) mName = value End Set End Property ‘ Read-only property Private mPowerLevel As Integer Public ReadOnly Property PowerLevel() As Integer Get Return mPowerLevel End Get End Property ‘ Write-only property Private mHeight As Double Public WriteOnly Property Height() As Double Set(ByVal value As Double) mHeight = If(value < 0, mHeight = 0, mHeight = value) End Set End Property |
// Auto-implemented properties public string Name { get; set; } public int Size { get; protected set; } // Set default value in constructor // Traditional property implementation private string name; public string Name { get { return name; } set { name = value; } } // Read-only property private int powerLevel; public int PowerLevel { get { return powerLevel; } } // Write-only property private double height; public double Height { set { height = value < 0 ? 0 : value; } } |
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20.泛型的定义
‘ Enforce accepted data type at compile-time Dim numbers As New List(Of Integer) numbers.Add(2) numbers.Add(4) DisplayList(Of Integer)(numbers) ‘ Subroutine can display any type of List Sub DisplayList(Of T)(ByVal list As List(Of T)) For Each item As T In list Console.WriteLine(item) Next End Sub ‘ Class works on any data type Class SillyList(Of T) Private list(10) As T Private rand As New Random Public Sub Add(ByVal item As T) list(rand.Next(10)) = item End Sub Public Function GetItem() As T Return list(rand.Next(10)) End Function End Class ‘ Limit T to only types that implement IComparable Function Maximum(Of T As IComparable)(ByVal ParamArray items As T()) As T Dim max As T = items(0) For Each item As T In items If item.CompareTo(max) > 0 Then max = item Next Return max End Function |
// Enforce accepted data type at compile-time List numbers.Add(2); numbers.Add(4); DisplayList // Function can display any type of List void DisplayList foreach (T item in list) Console.WriteLine(item); } // Class works on any data type class SillyList private T[] list = new T[10]; private Random rand = new Random(); public void Add(T item) { list[rand.Next(10)] = item; } public T GetItem() { return list[rand.Next(10)]; } } // Limit T to only types that implement IComparable T Maximum T max = items[0]; foreach (T item in items) if (item.CompareTo(max) > 0) max = item; return max; } |
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21.代理与Lambda表达式
Delegate Sub HelloDelegate(ByVal s As String) Sub SayHello(ByVal s As String) Console.WriteLine(“Hello, “ & s) End Sub‘ Create delegate that calls SayHello Dim hello As HelloDelegate = AddressOf SayHello hello(“World”) ‘ Or hello.Invoke(“World”)__’ Use lambda expression (anonymous method) instead of a delegate Dim hello2 = Sub(x) Console.WriteLine(“Hello, “ & x) hello2(“World”) ‘ Use Func(Of T, TResult) delegate to call Uppercase Dim convert As Func(Of String, String) = AddressOf Uppercase Console.WriteLine(convert(“test”)) Function Uppercase(s As String) As String Return s.ToUpper End Function ‘ Declare and invoke lambda expression Console.WriteLine((Function(num As Integer) num + 1)(2)) ‘ Pass lambda expression as an argument TestValues(Function(x, y) x Mod y = 0) Sub TestValues(ByVal f As Func(Of Integer, Integer, Boolean)) If f(8, 4) Then Console.WriteLine(“true”) Else Console.WriteLine(“false”) End If End Sub |
delegate void HelloDelegate(string s); void SayHello(string s) { Console.WriteLine(“Hello, “ + s); } // C# 1.0 delegate syntax with named method HelloDelegate hello = new HelloDelegate(SayHello); hello(“World”); // Or hello.Invoke(“World”); // C# 2.0 delegate syntax with anonymous method HelloDelegate hello2 = delegate(string s) { Console.WriteLine(“Hello, “ + s); }; hello2(“World”); // C# 3.0 delegate syntax with lambda expression HelloDelegate hello3 = s => { Console.WriteLine(“Hello, “ + s); }; hello3(“World”); // Use Func Func Console.WriteLine(convert(“test”)); string Uppercase(string s) { return s.ToUpper(); } // Declare and invoke Func using a lambda expression Console.WriteLine(new Func // Pass lamba expression as an argument TestValues((x, y) => x % y == 0); void TestValues(Func if (f(8, 4)) Console.WriteLine(“true”); else Console.WriteLine(“false”); } |
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22.对类方法的扩展(如:String类)
扩展方法使您能够向现有类型“添加”方法,而无需创建新的派生类型、重新编译或以其他方式修改原始类型。
扩展方法规定类必须是一个静态类,EString是一个静态类,里面包含的所有方法都必须是静态方法。
msdn是这样规定扩展方法的:“扩展方法被定义为静态方法,但它们是通过实例方法语法进行调用的。 它们的第一个参数指定该方法作用于哪个类型,并且该参数以 this 修饰符为前缀。_”
Imports System.Runtime.CompilerServices Module StringExtensions <Extension()> Public Function VowelCount(ByVal s As String) As Integer Return s.Count(Function(c) “aeiou”.Contains(Char.ToLower(c))) End Function End Module ‘ Using the extension method Console.WriteLine(“This is a test”.VowelCount) |
public static class StringExtensions { public static int VowelCount(this string s) { return s.Count(c => “aeiou”.Contains(Char.ToLower(c))); } } // Using the extension method Console.WriteLine(“This is a test”.VowelCount()); 如果需要你要对DateTime类型扩展方法名为IsRange(判断是否在此时间范围内),代码如下: /// /// 此时间是否在此范围内 -1:小于开始时间 0:在开始与结束时间范围内 1:已超出结束时间 /// /// /// /// /// public static int IsRange(this DateTime t, DateTime startTime, DateTime endTime) { if (((startTime - t).TotalSeconds > 0)) { return -1; } if (((endTime - t).TotalSeconds < 0)) { return 1; } return 0; } 这里的扩展方法是用this DateTime打头,那么就可以这样调用 time.IsRange(t1,t2);//判断时间time是否在t1到t2的范围内 |
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23.事件的定义
Delegate Sub MsgArrivedEventHandler(ByVal message As String) Event MsgArrivedEvent As MsgArrivedEventHandler ‘ or to define an event which declares a delegate implicitly Event MsgArrivedEvent(ByVal message As String) AddHandler MsgArrivedEvent, AddressOf MyMsgArrivedCallback ‘ Won’t throw an exception if obj is NothingRaiseEvent MsgArrivedEvent(“Test message”) RemoveHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback Imports System.Windows.Forms Dim WithEvents MyButton As Button ‘ WithEvents can’t be used on local variable MyButton = New Button Sub MyButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyButton.Click MessageBox.Show(Me, “Button was clicked”, “Info”, _ MessageBoxButtons.OK, MessageBoxIcon.Information) End Sub |
delegate void MsgArrivedEventHandler(string message); event MsgArrivedEventHandler MsgArrivedEvent; // Delegates must be used with events in C# MsgArrivedEvent += new MsgArrivedEventHandler(MyMsgArrivedEventCallback); MsgArrivedEvent(“Test message”); // Throws exception if obj is null_ MsgArrivedEvent -= new MsgArrivedEventHandler(My_MsgArrivedEventCallback); using System.Windows.Forms; Button MyButton = new Button(); MyButton.Click += new System.EventHandler(MyButton_Click); void MyButton_Click(object sender, System.EventArgs e) { MessageBox.Show(this, “Button was clicked”, “Info”, MessageBoxButtons.OK, MessageBoxIcon.Information); } |
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24.LINQ语法
Dim nums() As Integer = {5, 8, 2, 1, 6} ‘ Get all numbers in the array above 4 Dim results = From n In nums Where n > 4 Select n ‘ Same thing using lamba expression results = nums.Where(Function(n) n > 4) ‘ Displays 5 8 6 For Each n As Integer In results Console.Write(n & “ “) Next Console.WriteLine(results.Count()) ‘ 3 Console.WriteLine(results.First()) ‘ 5 Console.WriteLine(results.Last()) ‘ 6 Console.WriteLine(results.Average()) ‘ 6.33333 results = results.Intersect({5, 6, 7}) ‘ 5 6 results = results.Concat({5, 1, 5}) ‘ 5 6 5 1 5 results = results.Distinct() ‘ 5 6 1 Dim Students() As Student = { New Student With {.Name = “Bob”, .Gpa = 3.5}, New Student With {.Name = “Sue”, .Gpa = 4.0}, New Student With {.Name = “Joe”, .Gpa = 1.9} } ‘ Get a list of students ordered by Gpa with Gpa >= 3.0 Dim goodStudents = From s In Students Where s.Gpa >= 3.0 Order By s.Gpa Descending Select s Console.WriteLine(goodStudents.First.Name) ‘ Sue |
int[] nums = { 5, 8, 2, 1, 6 }; // Get all numbers in the array above 4 var results = from n in nums where n > 4 select n; // Same thing using lamba expression results = nums.Where(n => n > 4); // Displays 5 8 6 foreach (int n in results) Console.Write(n + “ “); Console.WriteLine(results.Count()); // 3 Console.WriteLine(results.First()); // 5 Console.WriteLine(results.Last()); // 6 Console.WriteLine(results.Average()); // 6.33333 results = results.Intersect(new[] {5, 6, 7}); // 5 6 results = results.Concat(new[] {5, 1, 5}); // 5 6 5 1 5 results = results.Distinct(); // 5 6 1 Student[] Students = { new Student{ Name = “Bob”, Gpa = 3.5 }, new Student{ Name = “Sue”, Gpa = 4.0 }, new Student{ Name = “Joe”, Gpa = 1.9 } }; // Get a list of students ordered by Gpa with Gpa >= 3.0 var goodStudents = from s in Students where s.Gpa >= 3.0 orderby s.Gpa descending select s; Console.WriteLine(goodStudents.First().Name); // Sue |
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25.集合语法
Popular classes in System.Collections (stored as Object) ArrayList Hashtable Queue Stack Popular classes in System.Collections.Generic (stored as type T) List(Of T) SortedList(Of TKey, TValue) Dictionary(Of TKey, TValue) Queue(Of T) Stack(Of T) Popular classes in System.Collections.Concurrent (thread safe) BlockingCollection(Of T) ConcurrentDictionary(Of TKey, TValue) ConcurrentQueue(Of T) ConcurrentStack(Of T) Microsoft.VisualBasic (not recommended) Collection ‘ Store ID and name Dim students As New Dictionary(Of Integer, String) From { {123, “Bob”}, {444, “Sue”}, {555, “Jane”} } students.Add(987, “Gary”) Console.WriteLine(students(444)) ‘ Sue ‘ Display all For Each stu In students Console.WriteLine(stu.Key & “ = “ & stu.Value) Next ‘ Method iterator for custom iteration over a collection Iterator Function OddNumbers(ByVal lastNum As Integer) As System.Collections.IEnumerable For num = 1 To lastNum If num Mod 2 = 1 Then Yield num End If Next End Function ‘ 1 3 5 7 For Each num In OddNumbers(7) Console.Write(num & “ “) Next |
Popular classes in System.Collections (stored as Object) ArrayList Hashtable Queue Stack Popular classes in System.Collections.Generic (stored as type T) List SortedList Dictionary Queue Stack Popular classes in System.Collections.Concurrent (thread safe) BlockingCollection ConcurrentDictionary ConcurrentQueue ConcurrentStack No equivalent to Microsoft.VisualBasic.Collection // Store ID and name var students = new Dictionary { { 123, “Bob” }, { 444, “Sue” }, { 555, “Jane” } }; students.Add(987, “Gary”); Console.WriteLine(students[444]); // Sue // Display all foreach (var stu in students) { Console.WriteLine(stu.Key + “ = “ + stu.Value); } // Method iterator for custom iteration over a collection static System.Collections.Generic.IEnumerable { for (var num = 1; num <= lastNum; num++) if (num % 2 == 1) yield return num; } // 1 3 5 7 foreach (double num in OddNumbers(7)) { Console.Write(num + “ “); } |
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26.Attributes
Attributes是一种新的描述信息,我们既可以使用attributes来定义设计期信息(例如 帮助文件,文档的URL),还可以用attributes定义运行时信息(例如,使XML中的元素与类的成员字段关联起来)。我们也可以用attributes来创建一个“自描述”的组件。
| ‘ Attribute can be applied to anything
Public Class IsTestedAttribute
Inherits Attribute
End Class
‘ Attribute can only be applied to classes or structs
<AttributeUsage(AttributeTargets.Class Or AttributeTargets.Struct)>
Public Class AuthorAttribute
Inherits Attribute
Public Property Name As String
Public Property Version As Integer = 0
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
Class Shape
Sub Move()
‘ Do something…
End Sub
End Class | // Attribute can be applied to anything
public class IsTestedAttribute : Attribute
{
}
// Attribute can only be applied to classes or structs
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
public class AuthorAttribute : Attribute {
public string Name { get; set; }<br /> public int Version { get; set; }
public AuthorAttribute(string name) {<br /> Name = name;<br /> Version = 0;<br /> }<br />}
[Author(“Sue”, Version = 3)]
class Shape {
**[IsTested]**<br /> void Move() {<br /> _// Do something..._<br /> }<br />}<br />例:<br />public class AnyClass
{
[Obsolete(“Don’t use Old method, use New method”, true)]
static void Old( ) { }
static void New( ) { }
public static void Main( ) <br /> {<br /> Old( );<br /> }<br />}
在该实例中我们用到了”Obsolete”attribute,它标记了一个不该再被使用的语言元素(译者注:这里的元素为方法),该属性的第一个参数是string类型,它解释为什么该元素被荒弃,以及我们该使用什么元素来代替它。实际中,我们可以书写任何其它文本来代替这段文本。第二个参数是告诉编译器把依然使用这被标识的元素视为一种错误,这就意味着编译器会因此而产生一个警告。
当我们试图编译上面的上面的程序,我们会得到如下错误:
AnyClass.Old()’ is obsolete: ‘Don’t use Old method, use New method’ |
| —- | —- |
27.输入输出
Console.Write(“What’s your name? “) Dim name As String = Console.ReadLine() Console.Write(“How old are you? “) Dim age As Integer = Val(Console.ReadLine()) Console.WriteLine(“{0} is {1} years old.”, name, age) ‘ or Console.WriteLine(name & “ is “ & age & “ years old.”) Dim c As Integer c = Console.Read() ‘ Read single char Console.WriteLine(c) ‘ Prints 65 if user enters “A” |
Console.Write(“What’s your name? “); string name = Console.ReadLine(); Console.Write(“How old are you? “); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine(“{0} is {1} years old.”, name, age); // or Console.WriteLine(name + “ is “ + age + “ years old.”); int c = Console.Read(); // Read single char Console.WriteLine(c); // Prints 65 if user enters “A” |
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28.文件操作
Imports System.IO ‘ Write out to text file Dim writer As StreamWriter = File.CreateText(“c:\myfile.txt”) writer.WriteLine(“Out to file.”) writer.Close() ‘ Read all lines from text file Dim reader As StreamReader = File.OpenText(“c:\myfile.txt”) Dim line As String = reader.ReadLine() While Not line Is Nothing Console.WriteLine(line) line = reader.ReadLine() End While reader.Close() ‘ Write out to binary file Dim str As String = “Text data” Dim num As Integer = 123 Dim binWriter As New BinaryWriter(File.OpenWrite(“c:\myfile.dat”)) binWriter.Write(str) binWriter.Write(num) binWriter.Close() ‘ Read from binary file Dim binReader As New BinaryReader(File.OpenRead(“c:\myfile.dat”)) str = binReader.ReadString() num = binReader.ReadInt32() binReader.Close() |
using System.IO; // Write out to text file StreamWriter writer = File.CreateText(“c:\\myfile.txt”); writer.WriteLine(“Out to file.”); writer.Close(); // Read all lines from text file StreamReader reader = File.OpenText(“c:\\myfile.txt”); string line = reader.ReadLine(); while (line != null) { Console.WriteLine(line); line = reader.ReadLine(); } reader.Close(); // Write out to binary file string str = “Text data”; int num = 123; BinaryWriter binWriter = new BinaryWriter(File.OpenWrite(“c:\\myfile.dat”)); binWriter.Write(str); binWriter.Write(num); binWriter.Close(); // Read from binary file BinaryReader binReader = new BinaryReader(File.OpenRead(“c:\\myfile.dat”)); str = binReader.ReadString(); num = binReader.ReadInt32(); binReader.Close(); |
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