Inheritance And Interfaces : Interface « Class Module « VB.Net Tutorial

1. VB.Net Tutorial
2. Class Module
3. Interface

Imports System
Imports System.Collections

Public Interface Printable
  ReadOnly Property Print() As Integer
End Interface

Public Class Money
  Implements Printable

  Protected mTransactions As New ArrayList()

  ReadOnly Property Print() As Integer Implements Printable.Print
    Get
      Return mTransactions.Count
    End Get
  End Property

  Public Overridable ReadOnly Property Balance() As Double
    Get
      Dim result As Double = 0.0
      Dim i As Integer
      For i = 0 To mTransactions.Count - 1
        result += CDbl(mTransactions(i))
      Next
      Return result
    End Get
  End Property

  Public Sub Add(ByVal amount As Double)
    mTransactions.Add(amount)
  End Sub

  Public Sub Subtract(ByVal amount As Double)
    mTransactions.Add(-amount)
  End Sub
End Class

Public Class MyMoney
  Inherits Money

  Public Overrides ReadOnly Property Balance() As Double
    Get
      Return MyBase.Balance - Print * 2
    End Get
  End Property
End Class

Module Test
  Sub Main()
    Dim acc1 As New Money()

    acc1.Add(200)
    acc1.Subtract(40)
    acc1.Add(30)

    Console.Write("count: {0}, ", acc1.Print)
    Console.WriteLine("balance: {0}", acc1.Balance)

    Dim acc2 As New MyMoney()

    acc2.Add(200)
    acc2.Subtract(40)
    acc2.Add(30)

    Console.Write("count: {0}, ", acc2.Print)
    Console.WriteLine("balance: {0}", acc2.Balance)
  End Sub
End Module

count: 3, balance: 190
count: 3, balance: 184