如果此程序改写为﹕

'ex09.bas
'Some Error Here!
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
'----------------------------------------------
Class Tree
Private varity As String
Private age As Integer
Private height As Single
Private Sub input(ByVal hei As Single)
height = hei
End Sub
End Class
'-----------------------------------------------
Public Class Form1
Inherits System.WinForms.Form

Public Sub New()
MyBase.New()
Form1 = Me
'This call is required by the Win Form Designer.
InitializeComponent()
'TODO: Add any initialization after the InitializeComponent() call
End Sub
'Form overrides dispose to clean up the component list.
Public Overrides Sub Dispose()
MyBase.Dispose()
components.Dispose()
End Sub
#Region " Windows Form Designer generated code "
.......
#End Region
Protected Sub Form1_Click( ByVal sender As Object, ByVal
e As System.EventArgs)
Dim a As New Tree()
a.input(2.1)
MessageBox("OK")
End Sub
End Class

这程序有问题﹐因为 input()是Tree类别之Private程序成员而非Public程序成员﹐所以不能使用如下格式──

所以此程序错了。 请再看个例子吧﹗

'ex10.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
'-------------------------------------------
Class Tree
Private varity As String
Private height As Single
Public age As Integer
Public Sub ShowAge()
MessageBox.Show("Age = " + str(Age))
End Sub
End Class
'-------------------------------------------
Public Class Form1
Inherits System.WinForms.Form

Public Sub New()
MyBase.New()
Form1 = Me
'This call is required by the Win Form Designer.
InitializeComponent()
'TODO: Add any initialization after the InitializeComponent() call
End Sub
'Form overrides dispose to clean up the component list.
Public Overrides Sub Dispose()
MyBase.Dispose()
components.Dispose()
End Sub
#Region " Windows Form Designer generated code "
.......
#End Region
Protected Sub Form1_Click( ByVal sender As Object, ByVal
e As System.EventArgs)
Dim a As New Tree()
a.age = 8
a.age = a.age + 2
a.ShowAge()
End Sub
End Class

Tree类别包含 2个Private成员── variety及height﹐且有 2个Public成员── age及 ShowAge()。由于age是Public资料成员﹐所以Fom1_Click()可使用格式──

来存取Tree内之age变量。指令── a.age = 8把8存入对象 a内之age 变量。指令──a.age = a.age + 2使对象a之age变量值加上2﹐成为10。由于ShowAge()程序是Public程序成员﹐也可使用格式──

来呼叫 ShowAge()程序。
由于类别（即对象）之目的是保护资料﹐并且提供程序成员来与外界沟通（接受、处理、并反应讯息）。通常﹐资料成员皆宣告为Private﹐而程序成员皆宣告为Public。亦即尽量少用格式──

而尽量多用格式──

例如﹕

'ex11.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
'--------------------------------------------------------------------
Class Tree
Private varity As String
Private age As Integer
Private height As Single
Public Sub input(ByVal v As String, ByVal a As Integer, ByVal hei As Single)
varity = v
age = a
height = hei
End Sub
Public Sub Show()
MessageBox.Show(varity + ", " + str(age) + ", " + str(height))
End Sub
End Class
'---------------------------------------------------------------------
Public Class Form1
Inherits System.WinForms.Form

(编辑:aniston)