VB.Net/Class/Overridable

Define Overridable Member Function

Imports System
Public Class MainClass
    Shared Sub Main(ByVal args As String())
      Dim circle As Circle
      circle = New Circle(37, 43, 2.5) " instantiate Circle
      Console.WriteLine( "X coordinate is " & circle.X & vbCrLf & _
         "Y coordinate is " & circle.Y & vbCrLf & "Radius is " & _
         circle.Radius )
      circle.X = 2
      circle.Y = 2
      circle.Radius = 4.25
      Console.WriteLine("The new location and radius of circle are " & _
         vbCrLf & circle.ToString() )
      Console.WriteLine( "Diameter is " & _
         String.Format("{0:F}", circle.Diameter()) )
      Console.WriteLine("Circumference is " & _
         String.Format("{0:F}", circle.Circumference()) )
      Console.WriteLine( "Area is " & String.Format("{0:F}", circle.Area()) )
    End Sub
End Class

Public Class Circle
   Inherits Point " Circle Inherits from class Point
   Private mRadius As Double
   " default constructor
   Public Sub New()
      " implicit call to Point constructor occurs here
      Radius = 0
   End Sub " New
   " constructor
   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer, ByVal radiusValue As Double)
      " use MyBase reference to Point constructor explicitly
      MyBase.New(xValue, yValue)
      Radius = radiusValue
   End Sub " New
   " property Radius
   Public Property Radius() As Double
      Get
         Return mRadius
      End Get
      Set(ByVal radiusValue As Double)
         If radiusValue > 0 Then
            mRadius = radiusValue
         End If
      End Set
   End Property " Radius
   " calculate Circle diameter
   Public Function Diameter() As Double
      Return mRadius * 2
   End Function " Diameter
   " calculate Circle circumference
   Public Function Circumference() As Double
      Return Math.PI * Diameter()
   End Function " Circumference
   " calculate Circle area
   Public Overridable Function Area() As Double
      Return Math.PI * mRadius ^ 2
   End Function " Area
   " return String representation of Circle
   Public Overrides Function ToString() As String
      " use MyBase reference to return Point String representation
      Return "Center = " & MyBase.ToString() & _
         "; Radius = " & mRadius
   End Function " ToString
End Class

Public Class Point
   " implicitly Inherits Object
   " point coordinate
   Private mX, mY As Integer
   " default constructor
   Public Sub New()
      " implicit call to Object constructor occurs here
      X = 0
      Y = 0
   End Sub " New
   " constructor
   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer)
      " implicit call to Object constructor occurs here
      X = xValue
      Y = yValue
   End Sub " New
   " property X
   Public Property X() As Integer
      Get
         Return mX
      End Get
      Set(ByVal value As Integer)
         mX = value
      End Set
   End Property " X
   " property Y 
   Public Property Y() As Integer
      Get
         Return mY
      End Get
      Set(ByVal value As Integer)
         mY = value
      End Set
   End Property " Y
   " return String representation of Point
   Public Overrides Function ToString() As String
      Return "[" & mX & ", " & mY & "]"
   End Function " ToString
End Class

Overridable Overloads Method from Base Class

Imports System
Imports System.Collections

Public Class MainClass
  Shared Sub Main()
    Dim e1 As New Programmer("E", 150000D)
    e1.RaiseSalary(0.1D) 
    Console.WriteLine(e1.TheName & " salary is now " & e1.Salary())
  End Sub
End Class

Public Class Employee
  Private m_Name As String
  Private m_Salary As Decimal
  Public Sub New(ByVal theName As String, ByVal curSalary As Decimal)
    m_Name = theName
    m_Salary = curSalary
  End Sub
  Public ReadOnly Property TheName() As String
    Get
      Return m_Name
    End Get
  End Property
  Public ReadOnly Property Salary() As Decimal
    Get
      Return MyClass.m_Salary
    End Get
  End Property
  Public Overridable Overloads Sub RaiseSalary(ByVal Percent As Decimal)
      m_Salary = (1 + Percent) * m_Salary
  End Sub
End Class
Public Class Programmer
  Inherits Employee
  Public Sub New(ByVal theName As String, ByVal curSalary As Decimal)
    MyBase.New(theName, curSalary)
  End Sub
  Public Overloads Overrides Sub RaiseSalary(ByVal Percent As Decimal)
    MyBase.RaiseSalary(1.2D * Percent)
  End Sub
End Class

Use Overridable Function

Imports System
Public Class MainClass
    Shared Sub Main(ByVal args As String())
      " instantiate object of class Cylinder
      Dim cylinder As New Cylinder(12, 23, 2.5, 5.7)
      " properties get initial x-y coordinate, radius and height
      Console.WriteLine( "X coordinate is " & cylinder.X & vbCrLf & _
         "Y coordinate is " & cylinder.Y & vbCrLf & "Radius is " & _
         cylinder.Radius & vbCrLf & "Height is " & cylinder.Height )
      " properties set new x-y coordinate, radius and height
      cylinder.X = 2
      cylinder.Y = 2
      cylinder.Height = 10
      cylinder.Radius = 4.25
      " get new x-y coordinate and radius
      Console.WriteLine( "The new location, radius " & _
         "and height of cylinder are" & vbCrLf & "Center = [" & _
         cylinder.ToString() )
         
      " display Cylinder"s diameter
      Console.WriteLine( "Diameter is " & _
         String.Format("{0:F}", cylinder.Diameter()) )
      " display Cylinder"s circumference
      Console.WriteLine( "Circumference is " & _
         String.Format("{0:F}", cylinder.Circumference()) )
      " display Cylinder"s area
      Console.WriteLine("Area is " & _
         String.Format("{0:F}", cylinder.Area()) )
      " display Cylinder"s volume
      Console.WriteLine( "Volume is " & _
         String.Format("{0:F}", cylinder.Volume()) )
    End Sub
End Class

Public Class Cylinder
   Inherits Circle
   Private mHeight As Double
   " default constructor
   Public Sub New()
      Height = 0
   End Sub " New
   " four-argument constructor
   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer, ByVal radiusValue As Double, _
      ByVal heightValue As Double)
      " explicit call to Circle constructor
      MyBase.New(xValue, yValue, radiusValue)
      Height = heightValue " set Cylinder height
   End Sub " New
   " property Height
   Public Property Height() As Double
      Get
         Return mHeight
      End Get
      " set Cylinder height if argument value is positive
      Set(ByVal heightValue As Double)
         If heightValue >= 0 Then
            mHeight = heightValue
         End If
      End Set
   End Property " Height
   " override method Area to calculate Cylinder area
   Public Overrides Function Area() As Double
      Return 2 * MyBase.Area + MyBase.Circumference * mHeight
   End Function " Area
   " calculate Cylinder volume
   Public Function Volume() As Double
      Return MyBase.Area * mHeight
   End Function " Volume
   " convert Cylinder to String
   Public Overrides Function ToString() As String
      Return MyBase.ToString() & "; Height = " & mHeight
   End Function " ToString
End Class
Public Class Circle
   Inherits Point " Circle Inherits from class Point
   Private mRadius As Double
   " default constructor
   Public Sub New()
      " implicit call to Point constructor occurs here
      Radius = 0
   End Sub " New
   " constructor
   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer, ByVal radiusValue As Double)
      " use MyBase reference to Point constructor explicitly
      MyBase.New(xValue, yValue)
      Radius = radiusValue
   End Sub " New
   " property Radius
   Public Property Radius() As Double
      Get
         Return mRadius
      End Get
      Set(ByVal radiusValue As Double)
         If radiusValue > 0 Then
            mRadius = radiusValue
         End If
      End Set
   End Property " Radius
   " calculate Circle diameter
   Public Function Diameter() As Double
      Return mRadius * 2
   End Function " Diameter
   " calculate Circle circumference
   Public Function Circumference() As Double
      Return Math.PI * Diameter()
   End Function " Circumference
   " calculate Circle area
   Public Overridable Function Area() As Double
      Return Math.PI * mRadius ^ 2
   End Function " Area
   " return String representation of Circle
   Public Overrides Function ToString() As String
      " use MyBase reference to return Point String representation
      Return "Center = " & MyBase.ToString() & _
         "; Radius = " & mRadius
   End Function " ToString
End Class

Public Class Point
   " implicitly Inherits Object
   " point coordinate
   Private mX, mY As Integer
   " default constructor
   Public Sub New()
      " implicit call to Object constructor occurs here
      X = 0
      Y = 0
   End Sub " New
   " constructor
   Public Sub New(ByVal xValue As Integer, _
      ByVal yValue As Integer)
      " implicit call to Object constructor occurs here
      X = xValue
      Y = yValue
   End Sub " New
   " property X
   Public Property X() As Integer
      Get
         Return mX
      End Get
      Set(ByVal value As Integer)
         mX = value
      End Set
   End Property " X
   " property Y 
   Public Property Y() As Integer
      Get
         Return mY
      End Get
      Set(ByVal value As Integer)
         mY = value
      End Set
   End Property " Y
   " return String representation of Point
   Public Overrides Function ToString() As String
      Return "[" & mX & ", " & mY & "]"
   End Function " ToString
End Class