VB.Net中文教程(2) 继承与封装性(2)
.......
#End Region
Protected Sub Form1_Click( ByVal sender As Object,
ByVal e As System.EventArgs)
Dim crag As New Teacher("Crag", 38, 45000)
crag.modifyName("Crag Clinton")
MessageBox.Show( "AGE: " + str(crag.age) + ", SALARY: "
+ str(crag.salary))
End Sub
End Class
因为name是Person类别的私有资料，在子类别Teacher的modifyName()里不能使用此资料名称，所以错了。如果将Person类别定义为﹕
"ex03.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"---------------------------------------------------------
Class Person
Protected name As String
Public age As Integer
Public Sub New(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
Public Function GetName() As String
GetName = name
End Function
End Class
Class Teacher
Inherits Person
Public salary As Single
Public Sub New(ByVal na As String, ByVal a As Integer, ByVal sa As Single)
MyBase.New(na, a)
salary = sa
End Sub
Public Sub modifyName(ByVal na As String)
name = na
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 crag As New Teacher("Crag", 38, 45000)
crag.modifyName("Crag Clinton")
MessageBox.Show( "AGE: " + str(crag.age) + ", NAME: "
+ crag.GetName())
End Sub
End Class
此程序输出：
AGE: 42, NAME: Crag Clinton
此时﹐name为家族公用之资料﹐凡是Person之子孙类别皆可取用之。但家族外之程序（如 Form1_Click()程序）仍不得直接使用之。如果上述定义改为﹕
Class Person
Protected name As String
Private salary As Decimal
Public age As Integer
Public Sub New(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
End Class
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 "
.......
责任编辑：Lily
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