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   ► KBTo/From GuidesASP Classic  Print This     

ASP Classic and VB.Net Cross Reference Guide

By Mike Prestwood

ASP Classic versus VB.Net: A side by side comparison between ASP Classic and VB.Net.

ASP Classic

Version: This content is based on ASP Classic 3.0 released November 2000. The focus of this content is on server-side scripting.

This content focuses on topics in common among the languages documented here so this content most likely applies to earlier versions.

In addition, much of the ASP syntax presented here is in common with MS Access and VB Classic. Finally, the syntax for VB.Net is based on VB so some of it even applies to VB.Net because ASP is also based on VB.

VB.Net

Version: This content is based on Microsoft VB.Net 2008. All content was tested using Microsoft Visual Studio.Net 2008. 

This content focuses on topics in common among the languages documented here so this content most likely applies to earlier versions of VB.Net too.

In addition, some of the VB.Net syntax presented here will look similiar to MS Access/VB Classic (with notable differences) and to ASP Classic (with even more notable differences).

 
Tool Basics
 

Developer environment basics such as common file extensions, common keyboard shortcuts, etc.

Deployment Overview

[Other Languages] 
ASP Classic: 

With ASP Classic, you simply copy your files to a web server that is capable of running ASP pages. This includes your .ASP pages along with supporting files such as images, include files, and database files.

Optionally, you can also deploy a global.asa file which is used to code certain events like application start, application end, session start, and session end.

More Info / Comment
VB.Net: 

VB.Net projects require the .Net framework and any additional dependencies you've added such as Crystal Reports.

In Visual Studio.Net, you can create a Setup and Deployment project by using any of the templates available on the New Project dialog (Other Project Types).

In addition, VB.Net projects also support ClickOnce which brings the ease of Web deployment to Windows Forms and console applications. To get started, right click on your solution in the Solution Explorer, click Properties then select the Security tab. 

In addition, you can use any of the many free and commercially available installation packages.





Development Tools

[Other Languages] 

Languages Focus

Primary development tool(s) used to develop and debug code.

ASP Classic: 

Microsoft Visual Interdev was popular for several  years but isn't used as much any more. Any good editor such as Microsoft Expression Web, etc. will work but debugging is left up to interactive skills.

More Info / Comment
VB.Net: 

Microsoft Visual Basic Express Editions (as in Visual Basic 2008 Express Edition) and the full version of Microsoft Visual Studio.Net are the current primary tools. VB.Net is not compatible with VB Classic.

More Info / Comment  




File Extensions

[Other Languages] 

Languages Focus

Common or primary file extensions used (not a complete list, just the basics).

ASP Classic:   .ASP

.asp is the default extension for Active Server Pages (ASP) although some developers will change the default extension in an effort to add an additional security level. Although there is no clear standard for include files, using .INC is common but you must make sure that .INC files are not executed nor displayed.

More Info / Comment
VB.Net: 

Common source code file extensions include:

  • .SLN - Solution File. Contains solution specific information such as links to the projects within this solution.
  • .VBPROJ - VB.Net Project File. Contains project specific information in XML. When adding a file, it is added to the project file.
  • .VB -VB.Net source file.
  • .Designer.VB -VB.Net form file (a text resource file).
Syntax Example:
//Sample code snippet from the .vbproj project file:
<ItemGroup>
  <Compile Include="Cyborg.vb" />
  <Compile Include="Form1.vb">
    <SubType>Form</SubType>
  </Compile>
  //...




Overview and History

[Other Languages] 
ASP Classic: 

Language Overview: Class-based language. Although you can create classes, ASP is not fully OOP. It is a traditional language with a few OOP extensions. You code in a traditional approach using functions, procedures, and global data, and you can make use of simple classes to help organize your reusable code.

Target Platforms: ASP Classic is most suitable for creating websites targeting any browser (IIS Web Server with ASP Classic installed or equivalent).

More Info / Comment
VB.Net: 

Language Overview: VB.Net is an OOP language (no global functions or variables). You code using a fully OOP approach (everything is in a class).

Target Platforms: VB.Net is most suitable for creating .Net Framework applications. This includes desktop business application using WinForms and websites using WebForms.

More Info / Comment




Report Tools Overview

[Other Languages] 

Languages Focus

Built-In: Some development tools have a reporting tool built-in and some do not. For example, typically desktop databases such as Paradox and Access have a built-in reporting tool and typically that reporting tool is used with nearly every application built with it. A built-in reporting tool makes development of reports across many clients and applications consistent and therefore easy.

Add-On: Development tools that do not have a built-in reporting tool need to use either a currently bundled report writer, or one of the popular reporting tools that integrates well with the development tool. For example, popular reporting tools include Crystal Reports, ReportBuilder, and MS SQL Reporting Services (tied to MS SQL).

ASP Classic: 

No built-in report writer but because ASP Classic targets a client browser (a document interfaced GUI), a common solution is to simply output an HTML formatted page with black text and a white background (not much control but it does work for some situations).

More Info / Comment
VB.Net: 

Microsoft includes ReportViewer Starting with Visual Studio 2005. You can even surface this .Net solution in your VB Classic application if you wish.

For WebForm applications the client target is the browser (a document interfaced GUI), a common solution is to simply output an HTML formatted page with black text and a white background (not much control but it does work for some situations).

For WinForm applications, Crystal Reports is still very popular with VB.Net developers because it has been bundled with Visual Basic since VB 3, it's overall popularity, and compatibility with many different development tools.





 
Language Basics
 

Language basics is kind of a catch all for absolute beginner stuff. The items (common names) I chose for language basics is a bit random and include items like case sensitivity, commenting, declaring variables, etc.

Case Sensitivity

[Other Languages] 

Languages Focus

Case sensitiviy in this case is referring to commands and variable names. For example, are "printf" and "PrintF" equivalent? Are fullname and FullName equivalent? When you create commands, operations, methods, or variables should you worry about case?

ASP Classic:   No

ASP Classic is not case sensitive. My preference for all languages where case sensitivity does not matter is to use camel caps as in the first example above. Many developers coming from a case sensitive language prefer to use all lowercase.

Syntax Example:  

You can use any of the following:

Response.Write "Hello"
response.write "Hello"
RESPONSE.WRITE "Hello"
REsponse.WritE "Hello"
VB.Net:   No

VB.Net is not case sensitive. If you type any other case for commands or variables, VB.Net will change it to the accepted or defined case. For example, if you type messagebox.show it is converted to MessageBox.Show.

Syntax Example:  

The following code works:

MessageBox.Show("hello")




Code Blocks

[Other Languages] 

Languages Focus

The rules for code blocks within a language dictate where you can declare variables, how you "bracket" code, etc.

ASP Classic:   End Xxx

In .ASP html pages, you embed ASP code between <% and %>.

ASP Classic code blocks are surrounded by statement ending keywords that all use End such as End Sub, End If, and WEnd.

Syntax Example:
<%
Sub x
End Sub
 
If x Then
End If
 
While x
WEnd
%>
VB.Net:   End Xxx

VB.Net, like VB Classic code blocks, are surrounded by statement ending keywords that all use End such as End Class, End Sub, End Function, and End If.

Syntax Example:
Public Class Dog
End Class
 
Protected Sub MySub
End Sub
  
Public Shared Function MySharedFunction() As Integer
MySharedFunction = 12345
End Function
 
If x Then
End If




Comments

[Other Languages] 

Languages Focus

Commenting code generally has three purposes: to document your code, for psuedo coding prior to coding, and to embed compiler directives. Most languages support both a single line comment and a multiple line comment. Some languages also use comments to give instructions to the compiler or interpreter.

ASP Classic:   ' or REM

Commenting Code
ASP Classic, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). ASP Classic does NOT have a multiple line comment.

Preprocessor Directives - @ and #
An @ is used for preprocessor directives within ASP code (within <% %>) and a # is used for HTML-style preprocessor directives.

Note: ASP Classic does not support VB Classic's #If directive.

Syntax Example:
'Single line comment.
REM Old school single line comment.

 

Common Preprocessor Directives include:

<%@LANGUAGE=VBScript%>
<!-- #Include File="includes.inc" -->
VB.Net:   ' or REM

Commenting Code
VB.Net, like all the VB-based languages, uses a single quote (') or the original class-style basic "REM" (most developers just use a quote). VB.Net does NOT have a multiple line comment.

Syntax Example:
'Single line comment.

REM Old school single line comment.

 






Constants

[Other Languages] 

General Info: Computer Language Constants

A constant is just like a variable (it holds a value) but, unlike a variable, you cannot change the value of a constant.

ASP Classic:   Const kPI = 3.1459

Scope can be Public or Private. Public Const is the same as just specifying Const. As with variables, all constants are variants. You do not specify the type, it's implied.

Syntax Example:
Const kPI = 3.1459
Const kName = "Mike"
 
//Public variable:
Public Const kFeetToMeter=3.28, kMeterToFeet=.3
VB.Net:   Const kPI Double = 3.1459

In VB.Net, you define constants with the Const keyword.

All constants are part of a class (no global constants) but you can make a constant public and have access to it using ClassName.ConstantName so long as you have added the class to the project. This works even without creating the class as if the public constants were static, but you cannot use the Shared keyword.

Constants must be of an integral type (sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, bool, or string), an enumeration, or a reference to null.

Syntax Example:
Public Class Convert
Inherits System.Object
 
  Public Const kName As String = "Mike"
  Private Const kPI Double = 3.1459
 
  //Declare two or more on same line too:
Const kFeetToMeter = 3.2808, kMeterToFeet = 0.3048
End Class




End of Statement

[Other Languages] 

Languages Focus

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

ASP Classic:   Return

A return marks the end of a statement and you cannot combine statements on a single line of code. You can break a single statement into two or more code lines by using a space and underscore " _".

Syntax Example:
Response.Write("Hello1")
Response.Write("Hello2")
Response.Write("Hello3")

'The following commented code on a single line does not work...
' Response.Write("Hello4") Response.Write("Hello5")

'Two or more lines works too with a space+underscore:
Response.Write _
("Hello6")
VB.Net:   Return

A return marks the end of a statement and you cannot combine statements on a single line of code. You can break a single statement into two or more code lines by using a space and underscore " _".

Syntax Example:  
Console.WriteLine("Hello1")
Console.WriteLine("Hello2")
Console.WriteLine("Hello3")

'The following commented code
'on a single line does not work...
'Console.WriteLine("Hello4") Console.WriteLine("Hello5")

'Two or more lines works too with a space+underscore:
Console.WriteLine _
"Hello6";




Literals

[Other Languages] 

General Info: Programming Literals

A value directly written into the source code of a computer program (as opposed to an identifier like a variable or constant). Literals cannot be changed. Common types of literals include string literals, floating point literals, integer literals, and hexidemal literals. Literal strings are usually either quoted (") or use an apostrophe (') which is often referred to as a single quote. Sometimes quotes are inaccurately referred to as double quotes.

Languages Focus

In addition to understanding whether to use a quote or apostrophe for string literals, you also want to know how to specify and work with other types of literals including floating point literals. Some compilers allow leading and trailing decimals (.1 + .1), while some require a leading or trailing 0 as in (0.1 + 0.1). Also, because floating point literals are difficult for compilers to represent accurately, you need to understand how the compiler handles them and how to use rounding and trimming commands correctly for the nature of the project your are coding.

ASP Classic:   quote

String literals are quoted as in "Prestwood". If you need to embed a quote use two quotes in a row.

To specify a floating point literal between 1 and -1, you can preceed the decimal with a 0 or not (both work). In other words, preceding and following decimals are allowed (both .1 and 0.1). Trailing decimals are also allowed (1, 1., and 1.0 are all equivalent and allowed).

Syntax Example:
Response.Write "Hello"
Response.Write "Hello ""Mike""."
  
'Does ASP evaluate this simple
'floating point math correctly? No! 
If (.1 + .1 + .1) = .3 Then
 Response.Write "Correct"
Else
 Response.Write "Not correct"
End If
VB.Net:   quote

String literals are quoted as in "Prestwood". If you need to embed a quote use two quotes in a row.

To specify a floating point literal between 1 and -1, preceed the decimal with a 0. If you don't, the compiler will auto-correct your code and place a leading 0. It will change .1 to 0.1 automatically. Trailing decimals are not allowed.

Syntax Example:  
Console.WriteLine("Hello")
Console.WriteLine("Hello ""Mike"".")
  
'Does VB.Net evaluate this simple
'floating point math correctly? No! 
If (.1 + .1 + .1) = 0.3 Then
MsgBox "Correct"
Else
MsgBox "Not correct"
End If




Variables

[Other Languages] 

Languages Focus

A variable holds a value that you can use and change throughout your code so long as the variable is within scope. With variable declaration, you not only want to know the syntax of how you declare a variable but you also want to know where. Are you allowed to declare a variable inline? What are the available scopes: local vs. global. Can you assign a value at the same time you declare a variable?

ASP Classic:   Dim x

ASP Classic is a loosely typed language. No variable types in ASP (all variables are variants). Declaring variables is even optional unless you use the Option Explicit statement to force explicit declaration of all variables with Dim in that script. Using Option Explicit is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope.

For example, at the top of my common include file, I have the following:

<%@LANGUAGE=VBScript%>
<%
Option Explicit
'...more code here.
%>
Syntax Example:
Dim Fullname
Dim Age
Dim Weight
 
FullName = "Mike Prestwood"
Age = 32
Weight = 154.4
 
'Declaritive assignment not supported:
''Dim Married = "Y"   '>>>Not supported.
VB.Net:   Dim x As Integer=0

Variables are case sensitive but VS.Net will auto-fix your variable names to the defined case. You can declare variables in-line wherever you need them and declarative variable assignment is supported.

Syntax Example:  

Dim FullName As String

Dim Age As Integer

Dim Weight As Double

FullName = "Mike Prestwood"

Age = 32

Weight = 154.4

'Declaritive variable assignment:

Dim Married As String = "Y"

MsgBox(Married)





 
Language Details
 

Language Details is kind of a catch all for stuff that didn't make it into language basics nor any other category.

Custom Routines

[Other Languages] 

Languages Focus

For non-OOP languages, a custom routine is a function, procedure, or subroutine and for pure OOP languages, a custom routine is a class method. Hybrid languages (both non-OOP and OOP) combine both.

ASP Classic:   Sub, Function

ASP Classic is a non-OOP language with some OOP features. It offers both Subs and Functions. A Sub does not return a value while a Function does. When Subs and Functions are used in a defined class, they become the methods of the class.

Syntax Example:
Sub SayHello(ByVal pName)
  Response.Write "Hello " + pName + "!<br>"
End Sub
 
Function Add(ByRef pN1, ByRef pN2)
  Add = pN1 + pN2
End Function
VB.Net:   Sub, Function

VB.Net is a fully OOP language so both Subs and Functions are methods of a class. A Sub does not return a value while a Function does.

Syntax Example:  
Private Sub DoSomething(ByVal pMsg As String)
'...some code.
End Sub

Private Function GetAge(ByVal x As String) As Integer
GetAge = 7
End Function




Inline Code

[Other Languages] 

Languages Focus

Also known as embedded code where you embed another syntax language within the native code of the development environment you are using. The inline code can be compiled by the current development's compiler or by an external compiler.

Do not confuse with inlining which is a coding technique where custom routines are moved inline where the code is executed either by you, by a compiler directive, or automatically by the compiler.

ASP Classic:   Not Supported
VB.Net:   Not Supported

Since all the .Net languages compile into intermediate language (IL), and not to a specific CPU, they do not provide support for inline assembler code.





Inlining

[Other Languages] 

General Info: Inline Routines

Instead of calling a routine, you move the code from the routine itself and expand it in place of the call. In addition to manual inlining, some languages support automatic inlining where the compiler or some other pre-compiler decides when to inline a code routine. Also, some languages allow for developer defined inlining where the developer can suggest and/or force the inlining of a code routine. Inlining can optimize your code for speed by saving a call and return, and parameter management.

Languages Focus

Does it support inlining? If so, does it support developer defined inlining? Does it support automatic inlining? Both?

ASP Classic:   Not Supported
VB.Net:   Automatic

In VB.Net, inlining is automatically done for you by the JIT compiler for all languages and in general leads to faster code for all programmers whether they are aware of inlining or not.

More Info / Comment  




Overloading

[Other Languages] 

Types of overloading include method overloading and operator overloading.

Method Overloading is where different functions with the same name are invoked based on the data types of the parameters passed or the number of parameters. Method overloading is a type of polymorphism and is also known as Parametric Polymorphism.

Operater Overloading allows an operator to behave differently based on the types of values used. For example, in some languages the + operator is used both to add numbers and to concatenate strings. Custom operator overloading is sometimes referred to as ad-hoc polymorphism.

ASP Classic:   Not Supported

ASP Classic does not support any type of overloading.

  • Operator - No.
  • Method - No.

Some developers like to pass in an array and then handle the array for a pseudo technique. Although not overloading, it's useful.

VB.Net:   Overloads, or implicit

VB.Net supports both method and operator overloading.

For method overloading, you either use implicit overloading (no special syntax like C#) or use the Overloads keyword. If you use the Overloads keyword, all overloaded methods with the same name in the same class must include the Overloads keyword.





Parameters

[Other Languages] 
ASP Classic:   ByRef, ByVal

By Reference or Value
For parameters, you can optionally specify ByVal or ByRef. ByRef is the default if you don't specify.

Syntax Example:  
Function SomeRoutine(ByRef pPerson, ByVal pName, Age)
VB.Net:   ByVal, ByRef

By Reference or Value
For parameters, you can optionally specify ByVal or ByRef. ByVal is the default if you don't specify which is changed from VB Classic (in VB Classic, ByRef was the default).

Syntax Example:  
Private Function Add(ByRef a As Integer, _
ByRef b As Integer) As Integer
  Add = a + b
End Function




Self Keyword

[Other Languages] 
ASP Classic:   me

Same as VB. The Me keyword is a built-in variable that refers to the class where the code is executing.

Syntax Example:
Class Cyborg
 Public CyborgName
 
 Public Function IntroduceYourself() 
  'Using Me. Prints Cameron.
  Response.Write("Hi, my name is " & Me.CyborgName & ".")
  
  'The above is just a demo. You could also not include "Me." 
  'in this case because we are in context of Me now. Using Me 
  'makes more sense when you start to pass Me as a parameter 
  'to a method.
 End Function 
End Class
VB.Net:   Me

To refer to the current instance of a class or structure, use the Me keyword. Me provides a way to refer to the specific instance in which the code is currently executing. It is particularly useful for passing information about the currently executing instance.

The Me keyword is also used as a modifier of the first parameter of an extension method.

You cannot use Me with static method functions because static methods do not belong to an object instance. If you try, you'll get an error.

Syntax Example:  
Sub SetBackgroundColor(FormName As Form)
  //FormName.BackColor = ...some color
End Sub
  
//Pass Me.
SetBackgroundColor(Me)




 
Data Structures
 

Data structures allow you to store and work with data. Common data structures include arrays, associative arrays, etc.

Array

[Other Languages] 

Languages Focus

A data structure in which individual values (called elements or items) may be located by reference to one or more integer index variables, the number of such indices being the number of dimensions in the array.

Arrays can start with an index value of 0 or 1, sometimes referred to as 0 based or 1 based.

ASP Classic:   x = Array()

Arrays in ASP Classic use a 0-based indice.

Use UBound to get the number of elements. UBound returns -1 if the array has no elements, 0 if it has 1, 1 if it has 2, etc.

Syntax Example:  
Dim MyArray, i
 
MyArray = Array("Mike", "Lisa", "Felicia", "Nathan")
 
If UBound(MyArray) > -1 Then
  For i = 0 to UBound(MyArray)
    Response.Write MyArray(i)
  Next
End If
[Not specified yet. Coming...]




Associative Array

[Other Languages] 
A set of unique keys linked to a set of values. Each unique key is associated with a value. Think of it as a two column table. MyArray['CA'] = 'California' MyArray['AR'] = 'Arizona'

Languages Focus

Associative arrays are also known as a dictionary or a hash table in other languages.

ASP Classic:   Scripting.Dictionary

Use the scriptiing dictionary object which is available on later versions of ASP Classic (all still commonly in use).

Note: Both Access VBA and VB Classic use a collection for this but collections are not supported in ASP Classic.

Syntax Example:
Dim StateList
 
set StateList = Server.CreateObject("Scripting.Dictionary")
StateList.Add "CA", "California"
StateList.Add "NV", "Nevada"
 
Response.Write "I live in " & StateList.Item("CA")
VB.Net:   Dictionary

An associative array links a set of keys to a set of values. In Visual Basic, associative arrays are implemented as Dictionaries.

This code produces a message box saying "Nevada."

Syntax Example:  
//Imports System.Collections.Generic
Dim States As New Dictionary(Of String, String)

States.Add("CA", "California")
States.Add("NV", "Nevada")
 
MsgBox(States("NV"))




Pointers

[Other Languages] 

General Info: Pointers / References

A pointer is a variable type that allows you to refer indirectly to another object. Instead of holding data, a pointer holds the address to data -- the address of another variable or object. You can change the address value a pointer points to thus changing the variable or object the pointer is pointing to.

A reference is a type of pointer that cannot change and it must always point to a valid storage (no nulls).

ASP Classic:   Not Supported

ASP Classic does not offer developer defined pointers.

VB.Net:   None

VB.Net doesn't support pointers. The closest it comes is IntPtr which you use to get pointer handles on windows, files, etc.

C# does have better support for pointers and C++/CLI has extensive support. One solution when it's really needed in VB.Net is to code in C# or C++/CLI and add it to your project.

However, VB.Net does support references.

More Info / Comment  




 
Statements
 

Common statements such as if statements, loops, etc.

Exception Trapping

[Other Languages] 

Languages Focus

A common usage of exception handling is to obtain and use resources in a "try-it" block, deal with any exceptions in an "exceptions" block, and release the resources in some kind of "final" block which executes whether or not any exceptions are trapped.

ASP Classic:   On Error
Syntax Example:
On Error Resume Next
Response.Write FormatDateTime(f_CurrentActualDate, vbShortDate)
  
  If ErrNumber <> 0 Then
Break(f_CurrentActualDate)
End If
On Error Goto 0
VB.Net:   Try...Catch...Finally

VB.Net uses a try...catch...finally statement to trap for errors.

Try
Catch
Finally
End Try
Syntax Example:
Try
Dim y As Integer = 0
y = 1 / y
Catch
MessageBox.Show("you cannot divide by zero")

End Try




If Statement

[Other Languages] 
ASP Classic:   If..ElseIf..Else..End If

The End If is optional if you put your code on a single line.

Syntax Example:
//Single line example.
If X = True Then Response.Write "hello" 
  
//Complete example.
If X = True Then
  '>>>do something.
ElseIf Y = "ABC" Then
  '>>>do something.
Else
  '>>>do something.
End If
VB.Net:   If..ElseIf..Else..End If

Same as VB classic.

Syntax Example:  
If x Then
MessageBox.Show("hello")
ElseIf Not x Then
MessageBox.Show("goodbye")
Else
MessageBox.Show("what?")
End If




 
Operators
 

A language symbol used for assignment, comparison, computational, or as a logical.

Assignment

[Other Languages] 

Languages Focus

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

ASP Classic:   =

ASP Classic uses = for it's assignment operator.

Syntax Example:
FullName = "Randy Spitz"
Age = 38
VB.Net:   =

VB.Net uses = for it's assignment operator.

Syntax Example:  
Dim Age As Integer
Dim FullName As String
  
FullName = "Randy Spitz"
Age = 38




Comparison Operators

[Other Languages] 

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

ASP Classic:   =, <>

Save as VB Classic. Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal
Syntax Example:
//Does ASP evaluate the math correctly? No!
If .1 + .1 + .1 = .3 Then
Response.Write "correct"
Else
Response.Write "not correct"
End If
VB.Net:   =, <>

Save as VB Classic. Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:  
//Does VB.Net evaluate the math correctly? No!
If 0.1 + 0.1 + 0.1 = 0.3 Then
MessageBox.Show("correct")
Else
MessageBox.Show("not correct")
End If




Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

ASP Classic:   Len(s&vbNullString)

In ASP Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  Response.Write("<br>Quotes with &'' say null is empty")
End If
 
If Len(s&"") = 0 Then
  Response.Write("<br>Len with &'' says null is empty")
End If
 
If Len(s&vbNullString) = 0 Then
  Response.Write("<br>Using vbNullString also works!")
End If
VB.Net:   String.IsNullOrEmpty

In .Net, a string can be null or empty. The .Net framework offers a static method in the string class: String.IsNullOrEmpty to check if a string is null or empty.

Syntax Example:  
Dim s As String 
  
's = "" 'Uncomment to test 2nd case.
  
If String.IsNullOrEmpty(s) Then
  MessageBox.Show("hello")
End If




Logical Operators

[Other Languages] 

Languages Focus

Logical operators perform conditional and, or, and not operations. Some languages support both binary logical operators that link two and unary logical operators negate (make opposite) the truth value of its argument. Finally, some languages short circuit logic. For example, with this or that, if this is an expression returning true, then that is never executed.

ASP Classic:   and, or, not

Same as VB. ASP Classic logical operators:

and and, as in this and that
or or, as in this or that
Not Not, as in Not This

ASP Classic never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

Syntax Example:
'Given expressions a, b, c, and d:
If Not (a and b) and (c or d) Then
  'Do something.
End If
VB.Net: 

VB.Net logical operators:

And and, as in this and that No Short Circuit
AndAlso and, as in this and that short circuits
Or or, as in this or that No Short Circuit
OrElse or, as in this or that short circuits
Not Not, as in Not This
Xor either or, as in this or that but not both

Syntax Example:  
'Given expressions a, b, c, and d:
If Not (a and b) and (c or d) Then
  'Do something.
End If




String Concatenation

[Other Languages] 
ASP Classic:  "String Concatenation" & or +

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

Syntax Example:
Dim FirstName
Dim LastName
 
FirstName  = "Mike"
LastName  = "Prestwood"
 
Response.Write "Full name: " & FirstName & " " + LastName
 
Response.Write "2+2=" + CStr(2+2)
VB.Net:  "String Concatenation" + or &

To concatenate two strings, use either the + or & operators. The & operator implicitly converts numbers. If you use the + operator to concatenate a string and a number, you have to cast the number as a string with CStr.

Alternatively, you can use the System.Text.StringBuilder class which frequently but not always provides faster code.

Syntax Example:
Dim FullName
Dim Age
  
//You can use + for strings.
FullName = "Prestwood"
Console.WriteLine("Hello " + FullName)
 
//For implicit casting, use &
Age = 35
Console.WriteLine(FullName & " is " & Age & " years old.")
'Implicit casting of numbers.
'
'This works:
MessageBox.Show(3.3)
  
'This fails:
'MessageBox.Show("" + 3.3)
  
'This works:
MessageBox.Show("" + CStr(3.3))
  
'Implicit casting &. This also works:
MessageBox.Show("" & 3.3)




Unary Operators

[Other Languages] 

General Info: Unary Operator

An operation with only one operand (a single input). Common unary operators include + plus, - minus, and bitwise not. Some operators can function as both unary and binary operators. For example, + and - operators can serve as either.

Languages Focus

What unary operators are supported in additoin to the standard plus, minus, and bitwise not.

ASP Classic: 

An operation with only one operand (a single input) such as +, -, and Not.

VB.Net: 

An operation with only one operand (a single input). A unary operator method can return any type but takes only one parameter, which must be the type of the containing class. In addition to the obvious +, -, and Not operators, VB.Net also offers:

isFalse
isTrue





 
Commands
 

Common commands (procedures and functions). A function returns a value. Optionally, it may also perform an action prior to returning a value. A procedure does not return a value or it returns void or null.

Left of String

[Other Languages] 
ASP Classic:   Left
Syntax Example:
Dim LeftString
LeftString = Left("Prestwood", 3)
Response.Write LeftString
VB.Net:  "Left of Substring" Left or Substring

The above usage of Left and Substring are equivalent.

Left is a traditional VB approach popular with developers moving from VB Classic to VB.Net. Substring is considered the .Net way of doing string manipulation.

Syntax Example:
Dim FullName
FullName = "Prestwood"
Console.WriteLine("Hello " + Left(FullName, 4))
Console.WriteLine("Hello " + FullName.Substring(0, 4))




 
Database
 

This category documents connecting and using data including database commands, and common technologies used.

Edit Record

[Other Languages] 

Languages Focus

This common syntax name documents editing a record as a whole: add/insert, edit, post data, and delete.

ASP Classic:   AddNew, Update, Delete

In ASP, using ADO, you use RecordSet.AddNew to add a new record, Recordset.Update to post the record, and RecordSet.Delete to delete it. To edit a record, you open the RecordSet using an editable cursor.

Syntax Example:

The following code snippet adds a record to a given editable RecordSet with FullName and Created fields:

objRS.AddNew
objRS.Fields("FullName") = "Barack Obama"
objRS.Fields("Created")  = Now
objRS.Update
[Not specified yet. Coming...]




Filter Records

[Other Languages] 
ASP Classic:   Filter

In ASP, using ADO, you filter a set of records using the Filter property.

Syntax Example:
objRecordSet.Filter = "ExtEmpType='P'"
[Not specified yet. Coming...]




Find Record

[Other Languages] 

Languages Focus

Finding a record is about moving a cursor to a specific record within a set of records (documented here). In addition to finding a record, you can sort, filter, and loop a set of records (documented in their topics).

ASP Classic:   Find, Seek

In ASP, using ADO, you use Find and Seek to move a cursor of a RecordSet to a matching record.

Syntax Example:

Given a valid ADO recordset, the following code snippet finds a specific user and prints out their age:

TC.Find " UserID='mprestwood' "
Response.Write TC.Fields("Age")
[Not specified yet. Coming...]




Record Movement

[Other Languages] 

Languages Focus

Top, bottom, next, and previous.

ASP Classic:   MoveFirst, MoveLast, MoveNext

ASP uses MoveFirst, MoveLast, MoveNext, and MovePrevious to move a database cursor (a RecordSet).

objRecordSet.MoveNext
Syntax Example:

The following snippet moves to the second to last record of a given RecordSet object:

objRecordSet.MoveLast
objRecordSet.MovePrevious
[Not specified yet. Coming...]




Sort Records

[Other Languages] 
ASP Classic:   Sort

In ASP, using ADO, you sort a set of records using the Sort property.

Syntax Example:
objMembersRS.Sort = "FirstName"
[Not specified yet. Coming...]




 
OOP Basics
 

Some languages support object-based concepts such as Paradox, Access, and VB Classic. Other languages have OO extensions and fully support object orientation in a hybrid fashion (such as C++ and Dephi for Win32). Finally, some lanages such as C#, VB.Net, Prism, and Java are entirely written in OO. Meaning, every line of code written must occur within a class).

Base Class

[Other Languages] 

Languages Focus

When you create a class, it is either a base class or inherits from another class. Some languages require all classes to inherit from a common base class and some do not.

ASP Classic:   Not Supported
VB.Net:   System.Object

In VB.Net, the Object keyword is an alias for the base System.Object class and is the single base class all classes ultimately inherit from. Use the Inherits keyword to indicate the parent class and Inherits must precede all declarations in a class.

Syntax Example:  
'Specify both namespace and class:
Public Class Cyborg
Inherits System.Object
End Class
  
'Use Object alias for System.Objct:
Public Class Cyborg
Inherits Object
End Class
  
'Default when not specified is System.Object:
Public Class Cyborg
End Class




Class..Object

[Other Languages] 

Languages Focus

In short, a class is a data type, and an object is an instance of a class type. A class has methods (routines), properties (member variables), and a constructor. The current values of the properties is the current state of the object. The UML is one of the diagraming disciplines that allows you to document the various changing states of a series of objects.

ASP Classic:   Class..Set..New

Ultra-primitive (no inheritance) but useful and encourages you to think and design using objects. Unlike VB, you can have more than one class per file.

Classes in ASP do support member fields, properties, and methods.

Syntax Example:
'Declare class.
Class Cyborg
  Public Function IntroduceYourself() 
    Response.Write("Hi, I do not have a name yet.") 
  End Function 
End Class
 
'Create object from class.
Set T1 = new Cyborg
T1.IntroduceYourself() 
Set T1 = Nothing      'Be sure to clean up!
VB.Net:   Class..End Class..New

Declare and implement VB.Net classes after the form class or in their own .vb files. Unlike VB Classic, you can have more than one class in a .vb class file (VB classic uses .cls files for each class).

Syntax Example:

Class definition:

Public Class Cyborg
  Inherits Object
 
  Public Sub IntroduceYourself()
  MessageBox.Show("Hi, I do not have a name yet.")
 End Sub
End Class

Some event like a button click:

Dim T1 As New Cyborg
T1.IntroduceYourself()
//No need to clean up with managed classes.
//The garbage collector will take care of it.




Inheritance

[Other Languages] 

The concept of a class makes it possible to define subclasses that share some or all of the main class characteristics. This is called inheritance. Inheritance also allows you to reuse code more efficiently. In a class tree, inheritance is used to design classes vertically. (You can use Interfaces to design classes horizontally within a class tree.) With inheritance, you are defining an "is-a" relationship (i.e. a chow is-a dog). Analysts using UML call this generalization where you generalize specific classes into general parent classes.

ASP Classic:   Not Supported
VB.Net:   Inherits ParentClass

VB.Net uses the Inherits keyword followed by the parent class name. If you do not include Inherits, your class inherits from System.Object.

Syntax Example:

In the following example, a terminator T-600 is-an android. 

Public Class Android
End Class
 
Public Class T-600
  Inherits Android
End Class




Member Field

[Other Languages] 

Also known as a Class Field.

A class variable defined with a specific class visibility, usually private visibility. A member property is different than a member field. A member property uses a member field to store values through accessor methods (getters and setters). For example, it is common to use a private member field to store the current value of a property. The current values of all the class member fields is the current state of the object.

Languages Focus

What modifiers apply to member fields, if any? Typical member field modifiers include scope modifiers (private, protected, etc.) and read-only. Can you initialize the value of a member field when declared ensuring a default value?

ASP Classic: 

ASP Classic does support member fields, but, as usual, you cannot initialize the type nor value of a member field. The type is implied by usage.

Syntax Example:
Class Cyborg
  Private FSerialNumber
  
  Public FCyborgName
  Public FCyborgAge 
Public FSeriesID
End Class
VB.Net: 

In VB.Net you can set the visibility of a member field to any visibility: private, protected, public, friend or protected friend.

You can intialize a member field with a default when declared. If you set the member field value in your constructor, it will override the default value.

Finally, you can use the Shared modifier (no instance required) and ReadOnly modifier (similar to a constant).

Syntax Example:
Public Class Cyborg
  Private FSerialNumber As String = "A100"
 
  Public CyborgName As String
  Public CyborgAge As Integer
  Public Shared ReadOnly SeriesID As Integer = 100
End Class




Member Method

[Other Languages] 

Also known as a Class Method.

A code routine that belongs to the class or an object instance (an instance of the class). Methods that belong to the class are called class methods or static methods. Methods that belong to an object instance are called instance methods, or simply methods.

When a method returns a value, it is a function method. When no value is returned (or void), it is a procedure method.

Methods frequently use method parameters to transfer data. When one object instance calls another object instance using a method with parameters, you call that messaging.

ASP Classic:   Sub, Function

ASP classic uses the keywords sub and function. A sub does not return a value and a function does. Many programmers like to use the optional call keyword when calling a sub to indicate the call is to a procedure.

Syntax Example:
'Declare class.
Class Cyborg
  Public Function IntroduceYourself() 
    Response.Write("Hi, I do not have a name yet.") 
  End Function 
End Class
 
'Create object from class.
Set T1 = new Cyborg
T1.IntroduceYourself() 
VB.Net:   Sub, Function

VB.Net�uses the keywords sub and function. A sub does not return a value and a function does. Many programmers like to use the optional call keyword when calling a sub to indicate the call is to a procedure.

Syntax Example:

Class definition:

Public Class Cyborg
� Inherits Object
 
Public Sub IntroduceYourself()
��� MessageBox.Show("Hi, I do not have a name yet.")
� End Sub
End Class

Some event like a button click:

Dim T1 As New Cyborg
T1.IntroduceYourself()




Member Modifier

[Other Languages] 

Languages Focus

Traditional private, protected, public, etc. member modifiers are documented under the member visibility topic of the Cross Reference Encyclopedia. With member modifiers here, we address additional member modifiers such as method and field modifiers.

ASP Classic:  "Member Modifiers" Default

Other than visibility modifiers Public and Private, the only other member modifier available in ASP Classic is Default which is used only with the Public keyword in a class block. It indicates that the sub, function, or property is the default method for the class. You can have only one Default per class.

More Info / Comment
VB.Net:  "Member Modifiers"

The method modifiers include�MustOverride,�NotOverridable, Overridable, Overrides. Specify�VB.Net member modifiers as follows:

Public Overrides Function SomeFunction() As Double

The field modifiers include ReadOnly and Shared. Specify field modifiers as follows:

Public ReadOnly SomeField As String

More Info / Comment




Member Property

[Other Languages] 
ASP Classic:   Property..Get..Let

ASP classic uses the property keyword and special Get and Let methods to both get and set the values of properties.

Syntax Example:
Class Cyborg
 Private FCyborgName
 
 Public Property Get CyborgName()
  CyborgName = FCyborgName
 End Property
 
 Public Property Let CyborgName(pCyborgName)
  FCyborgName = pCyborgName
 End Property
End Class
VB.Net:   property, get, set

VB.Net uses a special property keyword along with special get and set methods to both get and set the values of properties. For a read-only property, leave out the set method. The value keyword is used to refer to the member field. Properties can make use of any of the access modifiers (private, protected, etc).

My preference for VB.Net code is to start member fields with "F" ("FName" in our example) and drop the "F" with properties that manage member fields ("Name" in our example).

Syntax Example:
Public Class Cyborg
Private FCyborgName As String
 
  Public Property CyborgName()
Get
Return F
CyborgName
End Get
 
Set(ByVal value)
F
CyborgName = value
End Set
End Property
End Class




Member Visibility

[Other Languages] 

General Info: Class Visibility Specifiers

In OOP languages, members of a class have a specific scope that indicates visibility. Standard visibility includes private, protected, and public. Private members are usable by the defining class only (fully encapsulated). They are invisible outside of the class except by friendly classes. Protected members are usable by the defining class and descendant classes only (plus friendly classes). Public members are usable wherever its class can be referenced.

Languages Focus

Traditional member visibility specifiers for fully OOP languages are private, protected, and public. Many modern OOP languages implement additional member visibilities.

Additional member modifiers are documented under the Member Modifiers topic.

ASP Classic:   Private, Public

The member visibility modifiers are Private and Public. If not specified, the default is Public. Private and Public have the usual meaning. Private members are visible only within the class block. Public members are visible within the class and outside of the class.

Syntax Example:
Class Cyborg
  Private FSerialNumber  
  Public FCyborgName
  
  Public Function IntroduceYourself() 
Response.Write("Hi, I do not have a name yet.")
End Function
End Class
VB.Net:  "Access Modifiers"

In VB.Net, you specify each class and each class member's visibility with an access modifier preceding class or member. The VB.Net access modifiers are the traditional Public, Protected, and Private plus the two additional .Net modifiers Friend and Protected Friend.

Friend indicates members are accessible from types in the same assembly. Protected Friend indicates members are accessible from types in the same assembly as well as descendant classes. OO purist might object to Friend and Protected Friend and I suggest you avoid them until you both fully understand them and have a need that is best suited by them.

Syntax Example:
Public Class Cyborg
Inherits Object
 
  Private FName As String
End Class




 
OOP Details
 

More object oriented (OO) stuff.

Abstraction

[Other Languages] 

General Info: Abstract Class / Abstract Member

An abstract class member is a member that is specified in a class but not implemented. Classes that inherit from the class will have to implement the abstract member. Abstract members are a technique for ensuring a common interface with descendant classes. An abstract class is a class you cannot instantiate. A pure abstract class is a class with only abstract members.

Languages Focus

Abstraction is supported at various levels with each language. A language could enforce abstraction at the class level (either enforcing a no-instantiation rule or a only abstract members rule), and with class members (member methods and/or properties).

ASP Classic:   Not Supported
VB.Net:   MustInherit, MustOverride, Overrides

VB.Net supports abstract class members and abstract classes using the MustInherit and MustOverride modifiers.

An abstract class is indicated with a MustInherit modifier and is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties.

An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the MustOverride keyword. Then you override it in a descendant class with Overrides.

Syntax Example:
Public MustInherit Class Cyborg
  Public MustOverride Sub Speak(ByVal pMessage As String)
End Class

Public Class Series600
  Inherits Cyborg

  Public Overrides Sub Speak(ByVal pMessage As String)
    MessageBox.Show(pMessage)
  End Sub
End Class




Class Helper

[Other Languages] 

A. In Dephi, class helpers allow you to extend a class without using inheritance. With a class helper, you do not have to create and use a new class descending from a class but instead you enhance the class directly and continue using it as you always have (even just with the DCU).

B. In general terms, developers sometimes use the term to refer to any class that helps out another class.

ASP Classic:  "Class Helpers" Not Supported
VB.Net:  "Class Helpers" Not Supported

However, developers sometimes use the term "class helper" to refer to code that helps out a class. Not truly the meaning we are using here, but you should be aware of the term's general usage.





Code Contract

[Other Languages] 

A.k.a. Class Contract and Design by Contracts.

A contract with a method that must be true upon calling (pre) or exiting (post). A pre-condition contract must be true when the method is called. A post-condition contract must be true when exiting. If either are not true, an error is raised. For example, you can use code contracts to check for the validity of input parameters, and results

An invariant is also a code contract which validates the state of the object required by the method.

ASP Classic:  "Code Contracts" Not Supported
VB.Net:  "Code Contracts" Not Supported

Although not currently supported, there are plans for the next version of VS.Net and .Net using Requires and Ensures keywords. Look for code contracts in VS.Net 2010 and .Net 4.

If you code with VS.Net 2008 Pro or above and wish to implement contracts now, checkout the following download:





Constructor

[Other Languages] 

General Info: Class Constructor

Constructors are called when you instantiate an object from a class. This is where you can initialize variables and put code you wish executed each time the class is created. When you initially set the member fields and properties of an object, you are initializing the state of the object. The state of an object is the values of all it's member fields and properties at a given time.

Languages Focus

What is the syntax? Can you overload constructors? Is a special method name reserved for constructors?

ASP Classic:  "Constructors" Class_Initialize

When an object instance is created from a class, ASP calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, ASP calls a special sub called Class_Terminate.

Syntax Example:
Class Cyborg
  Public CyborgName
 
 Public Sub Class_Initialize
   Response.Write "<br>Class created"
   CyborgName = "Cameron"
  End Sub 
End Class
VB.Net:  "Constructors" New

In VB.Net, a constructor is called whenever a class or struct is created. A constructor is a sub named New. You can overload the constructor simply by adding two or more New subs with various parameters (overloaded constructors).

If you do not create a constructor, VB.Net will create an implicit constructor that initializes all member fields to their default values.

Constructors can execute at two different times. Static constructors are executed by the CLR before any objects are instantiated. Regular constructors are executed when you create an object.

You can invoke the parent constructor with MyBase.New.

Syntax Example:
Public Class Cyborg
Public CyborgName As String
  
  Public Sub New(ByVal pName As String)
CyborgName = pName
End Sub
End Class




Destructor

[Other Languages] 

General Info: Class Destructor

A special class method called when an object instance of a class is destroyed. With some languages they are called when the object instance goes out of scope, with some languages you specifically have to call the destructor in code to destroy the object, and others use a garbage collector to dispose of object instances at specific times.

Desctructors are commonly used to free the object instance but with languages that have a garbage collector object instances are disposed of when appropriate. Either way, destructors or their equivalent are commonly used to free up resources allocated in the class constructor.

Languages Focus

Are object instances freed with a garbage collector? Or, do you have to destroy object instances.

ASP Classic:   Class_Terminate

When an object instance is destroyed, ASP calls a special parameter-less sub named Class_Terminate. For example, when the variable falls out of scope. Since you cannot specify parameters for this sub, you also cannot overload it.

To explicitly destroy an object, use Set YourClass = nothing. If the Class object is explicitly destroyed, the client returns with the script engine error details.

When an object instance is created from a class, ASP calls a special sub called Class_Initialize.

Syntax Example:
Class Cyborg
  Public Sub Class_Terminate
    Response.Write "<br>Class destroyed"
End Sub
End Class
VB.Net:  "Finalizer" Finalize()

In VB.Net you cannot explicitly destroy a managed�object. Instead, the .Net Framework's garbage collector (GC) takes care of destroying all objects. The GC destroys the objects only when necessary. Some situations of necessity are when memory is exhausted or you explicitly call the System.GC.Collect() method. In general, you never need to call System.GC.Collect().

In .Net, a finalizer is used to free non-managed objects such as a file or network resource. In VB.Net, a finalizer is an overridden sub called Finalize. Because you don't know when the garbage collector will call your finalizer, Microsoft recommends you implement the IDisposable interface for non-managed resources and call it's Dispose() method at the appropriate time.

Syntax Example:
Class Cyborg
� Protected Overrides Sub Finalize()
��� 'Free non-managed resources here.
��� MyBase.Finalize()
� End Sub
End Class




Inheritance-Multiple

[Other Languages] 
ASP Classic:   Not Supported
VB.Net:   Not Supported

VB.Net does not support multiple implementation inheritance. Each class can have only one parent class (a single inheritance path). In VB.Net, you can use multiple interface usage to design in a multiple class way horizontally in a class hierarchy.

More Info / Comment




Interface

[Other Languages] 

An element of coding where you define a common set of properties and methods for use with the design of two or more classes.

Both interfaces and abstract classes are types of abstraction. With interfaces, like abstract classes, you cannot provide any implementation. However, unlike abstract classes, interfaces are not based on inheritance. You can apply an Interface to any class in your class tree. In a real sense, interfaces are a technique for designing horizontally in a class hierarchy (as opposed to inheritance where you design vertically). Using interfaces in your class design allows your system to evolve without breaking existing code.

ASP Classic:  "Interfaces" Not Supported

Although ASP Classic does support simple classes, it does not support interfaces.

VB.Net:  "Interfaces" Interface, Implements

With VB.Net you define an interface with the Interface keyword and use it in a class with the Implements keyword. In the resulting class, you implement each property and method and add Implements Interface.Object to each as in:

Sub Speak(ByVal pSentence As String) Implements IHuman.Speak
  MessageBox.Show(pSentence)
End Sub
Syntax Example:
Public Interface IHuman
'Specify interface methods and properties here.
End Interface

Public Class Cyborg
Inherits System.Object
End Class

Public Class CyborgHuman
Inherits Cyborg
Implements IHuman
'Implement interface methods and properties here.
End Class




Overriding

[Other Languages] 

General Info: Method Overriding

Where you define or implement a virtual method in a parent class and then replace it in a descendant class.

When you decide to declare a method as virtual, you are giving permission to derived classes to extend and override the method with their own implementation. You can have the extended method call the parent method's code too.

In most OO languages you can also choose to hide a parent method. When you introduce a new implementation of the same named method with the same signature without overriding, you are hiding the parent method.

ASP Classic:   Not Supported

Since ASP Classic does not support inheritance, there is no concept of a descendant class nor overriding.

VB.Net:   Overridable, Overrides

In VB.Net, you specify a virtual method with the Overridable keyword in a parent class and extend (or replace) it in a descendant class using the Overrides keyword.

Use the base keyword in the descendant method to execute the code in the parent method, i.e. base.SomeMethod().

Syntax Example:
Public Class Robot
Public Overridable Sub Speak()
MessageBox.Show("Robot says hi")
End Sub
End Class
  
Public Class Cyborg
Inherits Robot
  
  Public Overrides Sub Speak()
MessageBox.Show("hi")
End Sub
End Class




Partial Class

[Other Languages] 

A partial class, or partial type, is a class that can be split into two or more source code files and/or two or more locations within the same source file. Each partial class is known as a class part or just a part. Logically, partial classes do not make any difference to the compiler. The compiler puts the class together at compile time and treats the final class or type as a single entity exactly the same as if all the source code was in a single location.

Languages Focus

For languages that have implemented partial classes, you need to know usage details and restrictions. Can you split a class into two or more files? Can you split a class within a source code file into two or more locations? What are the details of inheritance? Does it apply to interfaces as well?

ASP Classic:  "Partial Classes" Not Supported
VB.Net:  "Partial Classes" Partial

VB.Net supports both partial classes and partial methods.

Syntax Example:
Partial Public Class Cyborg
Inherits System.Object
End Class




Polymorphism

[Other Languages] 

A coding technique where the same named function, operator, or object behaves differently depending on outside input or influences. Usually implemented as parameter overloading where the same named function is overloaded with other versions that are called either with a different type or number of parameters. Polymorphism is a general coding technique and other specific implementations are common such as inheritance, operator overloading, and interfaces.

Languages Focus

Many languages support built-in polymorphism such as a "+" operator that can add both integers and decimals. The following documents the ability to implement developer defined polymorphism.

[Not specified yet. Coming...]
VB.Net: 

VB.Net supports the following types of polymorphism:

More Info / Comment




Prevent Derivation

[Other Languages] 

Languages Focus

How do you prevent another class from inheriting and/or prevent a class from overriding a member.

ASP Classic:   Not Supported
VB.Net:   NotInheritable, NotOverridable

With VB.Net, use the NotInheritable keyword to prevent a class from being inherited from and use the NotOverridable keyword to prevent a method from being overridden.

A method marked NotOverridable must override an ancestor method. If you mark a class NotInheritable, all members are implicitly not overridable so the NotOverridable keyword is not legal.

Syntax Example:
Public Class Machine
  Public Overridable Sub Speak(ByRef pSentence As String)
MessageBox.Show(pSentence)
End Sub
End Class
  
Public Class Robot
Inherits Machine
  Public NotOverridable Overrides Sub Speak(ByRef pSentence As String)
MessageBox.Show(pSentence)
End Sub
End Class
  
Public NotInheritable Class Cyborg
Inherits Robot
End Class




Static Member

[Other Languages] 

General Info: Static Class / Static Member

A static member is a member you can have access to without instantiating the class into an object. For example, you can read and write static properties and call static methods without ever creating the class. Static members are also called class members (class methods, class properties, etc.) since they belong to the class and not to a specific object. A static class is a class that contains only static members. In the UML, these classes are described as utility classes.

Languages Focus

Languages that support static members usually at least support static member fields (the data). Some languages also support static methods, properties, etc. in which case the class member is held in memory at one location and shared with all objects. Finally, some languages support static classes which usually means the compiler will make sure a static class contains only static members.

ASP Classic:  "Static Members" Not Supported

Although ASP Classic supports the creation of simple classes, it does not support static methods.

VB.Net:  "Shared Members" Shared

VB.Net supports both static members and static classes (use the keyword Shared). You can add a static method, field, property, or event to an existing class.

You can designate a class as static and the compiler will ensure all methods in that class are static. You can add a constructor to a static class to initialize values.

The CLR automatically loads static classes with the program or namespace.

Syntax Example:
Public Shared Function MySharedFunction() As Integer
  MySharedFunction = 12345
End Function




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