vb.net & c# 对比 (摘抄)
2006-02-13 19:32
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| 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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| ' Single line only Rem Single line only | // Single line /* Multiple line */ /// XML comments on single line /** XML comments on multiple lines */ | ||||||||
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| Value Types Boolean Byte Char (example: "A"c) Short, Integer, Long Single, Double Decimal Date Reference Types Object String Dim x As Integer Console.WriteLine(x.GetType()) ' Prints System.Int32 Console.WriteLine(TypeName(x)) ' Prints Integer ' Type conversion 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) | Value Types bool byte, sbyte char (example: 'A') short, ushort, int, uint, long, ulong float, double decimal DateTime (not a built-in C# type) Reference Types object string int x; Console.WriteLine(x.GetType()); // Prints System.Int32 Console.WriteLine(typeof(int)); // Prints System.Int32 // Type conversion float d = 3.5f; int i = (int)d; // set to 3 (truncates decimal) | ||||||||
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| Const MAX_STUDENTS 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 MAX_STUDENTS = 25; // Can set to a const or var; may be initialized in a constructor readonly float MIN_DIAMETER = 4.93f; | ||||||||
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| 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) ' Prints "Stop is 1" Console.WriteLine(Status.Pass) ' Prints 70 Console.WriteLine(Status.Pass.ToString()) ' Prints 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); // Prints "Stop is 1" Console.WriteLine((int) Status.Pass); // Prints 70 Console.WriteLine(Status.Pass); // Prints Pass | ||||||||
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| Comparison = < > <= >= <> Arithmetic + - * / Mod / (integer division) ^ (raise to a power) Assignment = += -= *= /= /= ^= <<= >>= &= Bitwise And Or 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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| greeting = IIf(age < 20, "What's up?", "Hello") ' One line doesn't require "End If", no "Else" If language = "VB.NET" Then langType = "verbose" ' Use : to put two commands on same line If x <> 100 And y < 5 Then x *= 5 : y *= 2 ' Preferred If x <> 100 And y < 5 Then x *= 5 y *= 2 End If ' or to break up any long single command use _ If whenYouHaveAReally < longLine And itNeedsToBeBrokenInto2 > Lines Then _ UseTheUnderscore(charToBreakItUp) 'If x > 5 Then x *= y ElseIf x = 5 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 | greeting = age < 20 ? "What's up?" : "Hello"; if (x != 100 && y < 5) { // Multiple statements must be enclosed in {} x *= 5; y *= 2; } No need for _ or : since ; is used to terminate each statement. if (x > 5) x *= y; else if (x == 5) x += y; else if (x < 10) x -= y; else x /= y; switch (color) { // Must be integer or string case "pink": case "red": r++; break; // break is mandatory; no fall-through case "blue": b++; break; case "green": g++; break; default: other++; break; // break necessary on default } | ||||||||
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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 | 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++; } | ||||||||
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| 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 // C# can't dynamically resize an array. Just copy into new array. string[] names2 = new string[7]; Array.Copy(names, names2, names.Length); // or names.CopyTo(names2, 0); 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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| ' 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("Madonna") | // 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# doesn't support optional arguments/parameters. Just create two different versions of the same function. */ void SayHello(string name, string prefix) { Console.WriteLine("Greetings, " + prefix + " " + name); } void SayHello(string name) { SayHello(name, ""); } | ||||||||
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| Special character constants 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" ' Chars Dim letter As Char = school.Chars(0) ' letter is H 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 msg As String = "File is 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 Console.WriteLine(mascot.Substring(2, 3)) ' Prints "son" ' String matching If ("John 3:16" Like "Jo[Hh]? #:*") Then 'true Imports System.Text.RegularExpressions ' More powerful than Like Dim r As New Regex("Jo[hH]. /d:*") If (r.Match("John 3:16").Success) Then 'true ' My birthday: Oct 12, 1973 Dim dt As New DateTime(1973, 10, 12) Dim s As String = "My birthday: " & dt.ToString("MMM dd, yyyy") Console.WriteLine(s) ' 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 /n, /r /t // /" // String concatenation string school = "Harding/t"; school = school + "University"; // school is "Harding (tab) University" // Chars char letter = school[0]; // letter is H letter = Convert.ToChar(65); // letter is A letter = (char)65; // same thing char[] word = school.ToCharArray(); // word holds Harding // String literal string msg = @"File is c:/temp/x.dat"; // same as string msg = "File is 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 Console.WriteLine(mascot.Substring(2, 3)); // Prints "son" // String matching // No Like equivalent - use regular expressions using System.Text.RegularExpressions; Regex r = new Regex(@"Jo[hH]. /d:*"); if (r.Match("John 3:16").Success) // true // My birthday: Oct 12, 1973 DateTime dt = new DateTime(1973, 10, 12); string s = "My birthday: " + dt.ToString("MMM dd, yyyy"); // 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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| ' 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 { // Requires reference to the Microsoft.VisualBasic.dll // assembly (pre .NET Framework v2.0) Microsoft.VisualBasic.Interaction.Beep(); } | ||||||||
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| 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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| Accessibility keywords Public Private Friend Protected Protected Friend Shared ' Inheritance Class FootballGame Inherits Competition ... End Class ' Interface definition Interface IAlarmClock ... End Interface // Extending an interface Interface IAlarmClock Inherits IClock ... End Interface // Interface implementation Class WristWatch Implements IAlarmClock, ITimer ... End Class | Accessibility keywords public private internal protected protected internal static // Inheritance class FootballGame : Competition { ... } // Interface definition interface IAlarmClock { ... } // Extending an interface interface IAlarmClock : IClock { ... } // Interface implementation class WristWatch : IAlarmClock, ITimer { ... } | ||||||||
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| Class SuperHero Private _powerLevel As Integer Public Sub New() _powerLevel = 0 End Sub Public Sub New(ByVal powerLevel As Integer) Me._powerLevel = powerLevel End Sub Protected Overrides Sub Finalize() ' Desctructor code to free unmanaged resources MyBase.Finalize() End Sub End Class | class SuperHero { private int _powerLevel; public SuperHero() { _powerLevel = 0; } public SuperHero(int powerLevel) { this._powerLevel= powerLevel; } ~SuperHero() { // Destructor code to free unmanaged resources. // Implicitly creates a Finalize method } } | ||||||||
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| 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.") | SuperHero hero = new SuperHero(); // No "With" construct hero.Name = "SpamMan"; hero.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."); | ||||||||
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| Structure StudentRecord 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 StudentRecord = New StudentRecord("Bob", 3.5) Dim stu2 As StudentRecord = stu stu2.name = "Sue" Console.WriteLine(stu.name) ' Prints Bob Console.WriteLine(stu2.name) ' Prints Sue | struct StudentRecord { public string name; public float gpa; public StudentRecord(string name, float gpa) { this.name = name; this.gpa = gpa; } } StudentRecord stu = new StudentRecord("Bob", 3.5f); StudentRecord stu2 = stu; stu2.name = "Sue"; Console.WriteLine(stu.name); // Prints Bob Console.WriteLine(stu2.name); // Prints Sue | ||||||||
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| Private _size As Integer Public Property Size() As Integer Get Return _size End Get Set (ByVal Value As Integer) If Value < 0 Then _size = 0 Else _size = Value End If End Set End Property foo.Size += 1 | private int _size; public int Size { get { return _size; } set { if (value < 0) _size = 0; else _size = value; } } foo.Size++; | ||||||||
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| 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 My_MsgArrivedCallback ' Won't throw an exception if obj is Nothing RaiseEvent 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 Private 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(My_MsgArrivedEventCallback); 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); private void MyButton_Click(object sender, System.EventArgs e) { MessageBox.Show(this, "Button was clicked", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information); } | ||||||||
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| 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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| 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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