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VISUAL BASIC.NET

Polymorphism using Abstract Classes in Visual Basic.NET 2005
By: Jagadish Chaterjee
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    2007-08-01

    Table of Contents:
  • Polymorphism using Abstract Classes in Visual Basic.NET 2005
  • Life without the Abstract class in Visual Basic 2005: continued
  • Defining and implementing abstract classes in Visual Basic 2005: abstract class
  • Defining and implementing abstract classes in Visual Basic 2005: child class
  • Defining and implementing abstract classes in Visual Basic 2005: child classes continued
  • Making use of Polymorphism using abstract classes in Visual Basic 2005

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    Polymorphism using Abstract Classes in Visual Basic.NET 2005


    (Page 1 of 6 )

    This article gives you an in-depth understanding of abstract methods, abstract classes and polymorphism using abstract classes in Visual Basic 2005.
    A downloadable zip file is available for this article.

    If you are new to OOP in Visual Basic.NET, I strongly suggest that you go through the following links:

    Using Constructors with Object-Oriented Database Development

    Properties and Object-Oriented Database Development

    Using Methods with Object-Oriented Database Development

    An Introduction to Object-Oriented Database Development

    The entire source code for this article is available in the form of a downloadable zip file. The solution was developed using Microsoft Visual Studio 2005 Professional Edition on Microsoft Windows Server 2003 Enterprise Edition. I didn't really test it in any other environment. I request that you post in the discussion area if you have any problems in execution.

    Life without the "Abstract" class in Visual Basic 2005

    Before understanding the "Abstract" class, let us go through an example with a set of classes, which demonstrates the inconveniences of repeating the code.

    The following is a class named "Rectangle" defined with length and breadth as properties along with a method named "GetArea" to calculate the area of a rectangle:

    Public Class Rectangle

      Private _l As Double

      Private _b As Double

     

      Public Sub New(ByVal length As Double, ByVal breadth As Double)

        Me.L = length

        Me.B = breadth

      End Sub

     

      Public Property L() As Double

        Get

          Return _l

        End Get

        Set(ByVal value As Double)

          _l = value

        End Set

      End Property

     

      Public Property B() As Double

        Get

          Return _b

        End Get

        Set(ByVal value As Double)

          _b = value

        End Set

      End Property

     

      Public Function GetArea() As Double

        Return _l * _b

      End Function

     

    End Class

    There exists nothing special about the previous class apart from properties, methods and a constructor.  Let us consider two more classes, "EquiTriangle" and "Square," which have properties that are similar to those of our "Rectangle" class. This will be continued in the next section.

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