此时﹐salary为类别私有﹐其它类别不得使用。name为家族私有﹐家族外之类别不得使用。age为公用﹐任何类别皆可用。

1.2 公用与私有程序
上节介绍过﹕资料成员有 Private、Protected 及Public之分。同样地﹐程序成员也可分为 Private、Protected 及Public。虽然在应用上﹐程序成员大多定义为Public﹐但必要时﹐也能将过程定义为Private 或 Protected。私有程序和私有资料一样﹐只限于该类别之程序才能呼叫它。例如﹕

'ex04.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
'----------------------------------------------------------------------
Class Person
Private name As String
Private age As Integer
Private Sub modifyAge(ByVal a As Integer)
age = a
End Sub
Public Sub New(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
Public Sub modify(ByVal na As String, ByVal a As Integer)
name = na
modifyAge(a)
End Sub
Public Sub Show()
Messagebox.Show("Name: " + name + " 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 p1 As New Person("David", 25)
p1.Show()
p1.modify("David Smith", 28)
p1.Show()
End Sub
End Class

此程序输出：
Name: David Age: 25
Name: David Smith Age: 45

modifyAge()为私有程序﹐New()及modify()为公用程序。modifyAge()为Person类别之程序成员﹐所以modify()能呼叫modifyAge()。Person类别外之函数不能呼叫modifyAge()。例如﹕在Form1_Click()中﹐可写着 p1.modify()﹐因为modify()为公用程序。但于Form1_Click()内﹐就不可写着 p1.modifyAge()﹐因为modifyAge()为 Private函数。如果放宽对modifyAge()之限制﹐使Person之子类别能呼叫modifyAge()﹐就须定义modifyAge()为 Protected函数﹐如下﹕

'ex05.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
'----------------------------------------------------------------------
Class Person
Protected name As String
Private age As Integer
Protected Sub modifyAge(ByVal a As Integer)
age = a
End Sub
Public Sub New(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
Public Sub Show()
Messagebox.Show("Name: " + name + " Age: " + str(age))
End Sub
End Class

Class Teacher
Inherits Person

Public Sub New(ByVal na As String, ByVal a As Integer)
MyBase.New(na, a)
End Sub
Public Sub modify(ByVal na As String, ByVal a As Integer)
MyBase.name = na
MyBase.modifyAge(a)
End Sub
End Class
'-------------------------------------------------------------------
Public Class Form1
Inherits System.WinForms.Form

(编辑:aniston)