VB.Net is an object oriented programming language. In Object Oriented Programming methodology, a program consists
of various objects that interact with each other by means of actions. The actions that an object may take are called methods.
Objects of the same kind are said to have the same type or, more often, are said to be in the same class. When we consider a VB.Net program it can be defined as a collection
of objects that communicate via invoking each other's methods. Let us
now briefly look into what do class, object, methods and instant
variables mean.
- Object - Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors - wagging, barking, eating, etc. An object is an instance of a class.
- Class - A class can be defined as a template/blueprint that describe the behaviors/states that object of its type support.
- Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
- Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant variables.
A Rectangle Class in VB.Net
For example, let us consider a Rectangle object. It has attributes like length and width. Depending upon the design,
it may need ways for accepting the values of these attributes, calculating area and display details. Let us look at an implementation of a Rectangle class and discuss VB.Net basic syntax, on the basis of our observations in it:
Imports System Public Class Rectangle Private length As Double Private width As Double 'Public methods Public Sub AcceptDetails() length = 4.5 width = 3.5 End Sub Public Function GetArea() As Double GetArea = length * width End Function Public Sub Display() Console.WriteLine("Length: {0}", length) Console.WriteLine("Width: {0}", width) Console.WriteLine("Area: {0}", GetArea()) End Sub Shared Sub Main() Dim r As New Rectangle() r.Acceptdetails() r.Display() Console.ReadLine() End Sub End Class
When the above code is compiled and executed, it produces the following result:
Length: 4.5 Width: 3.5 Area: 15.75
In previous chapter, we created a Visual Basic module that held the
code. Sub Main indicates the entry point of VB.Net program.
Here, we are using Class that contains both code and data. You use
classes to create objects. For example, in the code, r is a Rectangle
object.
An object is an instance of a class:
Dim r As New Rectangle()
A class may have members that can be accessible from outside class,
if so specified. Data members are called fields and procedure members
are called methods.
Shared methods or static methods can be invoked without creating an object of the class. Instance methods are invoked through an object of the class:
Shared Sub Main() Dim r As New Rectangle() r.Acceptdetails() r.Display() Console.ReadLine() End Sub
Identifiers
An identifier is a name used to identify a class, variable, function,
or any other user-defined item. The basic rules for naming classes in
VB.Net are as follows:
- A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.
- It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However an underscore ( _ ) can be used.
- It should not be a reserved keyword.
VB.Net Keywords
The following table lists the VB.Net reserved keywords:
AddHandler | AddressOf | Alias | And | AndAlso | As | Boolean |
ByRef | Byte | ByVal | Call | Case | Catch | CBool |
CByte | CChar | CDate | CDec | CDbl | Char | CInt |
Class | CLng | CObj | Const | Continue | CSByte | CShort |
CSng | CStr | CType | CUInt | CULng | CUShort | Date |
Decimal | Declare | Default | Delegate | Dim | DirectCast | Do |
Double | Each | Else | ElseIf | End | End If | Enum |
Erase | Error | Event | Exit | False | Finally | For |
Friend | Function | Get | GetType | GetXML Namespace | Global | GoTo |
Handles | If | Implements | Imports | In | Inherits | Integer |
Interface | Is | IsNot | Let | Lib | Like | Long |
Loop | Me | Mod | Module | MustInherit | MustOverride | MyBase |
MyClass | Namespace | Narrowing | New | Next | Not | Nothing |
Not Inheritable | Not Overridable | Object | Of | On | Operator | Option |
Optional | Or | OrElse | Overloads | Overridable | Overrides | ParamArray |
Partial | Private | Property | Protected | Public | RaiseEvent | ReadOnly |
ReDim | REM | Remove Handler | Resume | Return | SByte | Select |
Set | Shadows | Shared | Short | Single | Static | Step |
Stop | String | Structure | Sub | SyncLock | Then | Throw |
To | True | Try | TryCast | TypeOf | UInteger | While |
Widening | With | WithEvents | WriteOnly | Xor |
VB.Net - Data Types
Data types refer to an extensive system used for declaring variables or functions of different types.
The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted.
Data Types Available in VB.Net
VB.Net provides a wide range of data types. The following table shows all the data types available:
Data Type | Storage Allocation | Value Range |
---|---|---|
Boolean | Depends on implementing platform | True or False |
Byte | 1 byte | 0 through 255 (unsigned) |
Char | 2 bytes | 0 through 65535 (unsigned) |
Date | 8 bytes | 0:00:00 (midnight) on January 1, 0001 through 11:59:59 PM on December 31, 9999 |
Decimal | 16 bytes | 0 through +/-79,228,162,514,264,337,593,543,950,335 (+/-7.9...E+28)with no decimal point; 0 through +/-7.9228162514264337593543950335 with 28 places to the right of the decimal |
Double | 8 bytes | -1.79769313486231570E+308 through -4.94065645841246544E-324, for negative values 4.94065645841246544E-324 through 1.79769313486231570E+308, for positive values |
Integer | 4 bytes | -2,147,483,648 through 2,147,483,647 (signed) |
Long | 8 bytes | -9,223,372,036,854,775,808 through 9,223,372,036,854,775,807(signed) |
Object | 4 bytes on 32-bit platform 8 bytes on 64-bit platform | Any type can be stored in a variable of type Object |
SByte | 1 byte | -128 through 127 (signed) |
Short | 2 bytes | -32,768 through 32,767 (signed) |
Single | 4 bytes | -3.4028235E+38 through -1.401298E-45 for negative values;1.401298E-45 through 3.4028235E+38 for positive values |
String | Depends on implementing platform | 0 to approximately 2 billion Unicode characters |
UInteger | 4 bytes | 0 through 4,294,967,295 (unsigned) |
ULong | 8 bytes | 0 through 18,446,744,073,709,551,615 (unsigned) |
User-Defined | Depends on implementing platform | Each member of the structure has a range determined by its data type and independent of the ranges of the other members |
UShort | 2 bytes | 0 through 65,535 (unsigned) |
Example
The following example demonstrates use of some of the types:
Module DataTypes Sub Main() Dim b As Byte Dim n As Integer Dim si As Single Dim d As Double Dim da As Date Dim c As Char Dim s As String Dim bl As Boolean b = 1 n = 1234567 si = 0.12345678901234566 d = 0.12345678901234566 da = Today c = "U"c s = "Me" If ScriptEngine = "VB" Then bl = True Else bl = False End If If bl Then 'the oath taking Console.Write(c & " and," & s & vbCrLf) Console.WriteLine("declaring on the day of: {0}", da) Console.WriteLine("We will learn VB.Net seriously") Console.WriteLine("Lets see what happens to the floating point variables:") Console.WriteLine("The Single: {0}, The Double: {1}", si, d) End If Console.ReadKey() End Sub End Module
When the above code is compiled and executed, it produces the following result:
U and, Me declaring on the day of: 12/4/2012 12:00:00 PM We will learn VB.Net seriously Lets see what happens to the floating point variables: The Single:0.1234568, The Double: 0.123456789012346
The Type Conversion Functions in VB.Net
VB.Net provides the following inline type conversion functions:
S.N | Functionss & Description |
---|---|
1 | CBool(expression) Converts the expression to Boolean data type. |
2 | CByte(expression) Converts the expression to Byte data type. |
3 | CChar(expression) Converts the expression to Char data type. |
4 | CDate(expression) Converts the expression to Date data type |
5 | CDbl(expression) Converts the expression to Double data type. |
6 | CDec(expression) Converts the expression to Decimal data type. |
7 | CInt(expression) Converts the expression to Integer data type. |
8 | CLng(expression) Converts the expression to Long data type. |
9 | CObj(expression) Converts the expression to Object type. |
10 | CSByte(expression) Converts the expression to SByte data type. |
11 | CShort(expression) Converts the expression to Short data type. |
12 | CSng(expression) Converts the expression to Single data type. |
13 | CStr(expression) Converts the expression to String data type. |
14 | CUInt(expression) Converts the expression to UInt data type. |
15 | CULng(expression) Converts the expression to ULng data type. |
16 | CUShort(expression) Converts the expression to UShort data type. |
Example:
The following example demonstrates some of these functions:
Module DataTypes Sub Main() Dim n As Integer Dim da As Date Dim bl As Boolean = True n = 1234567 da = Today Console.WriteLine(bl) Console.WriteLine(CSByte(bl)) Console.WriteLine(CStr(bl)) Console.WriteLine(CStr(da)) Console.WriteLine(CChar(CChar(CStr(n)))) Console.WriteLine(CChar(CStr(da))) Console.ReadKey() End Sub End Module
When the above code is compiled and executed, it produces the following result:
True -1 True 12/4/2012 1 1
Source : http://www.tutorialspoint.com
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