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   ► KBTo/From GuidesASP ClassicOOP Basics  Print This     

Cross Ref > OOP Basics

By Mike Prestwood

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

 
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




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