VB.Net中文教程(1) 类别与封装性(2)
End Function
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 Tree = New Tree()
Dim h As Single
a.input(2.1)
h = a.inquireHeight()
Messagebox.Show("height = " + str(h) + "公尺", "HI!")
End Sub
End Class
此程序输出如下﹕height = 2.1公尺
Tree类别有2个程序成员──input() 和inquireHeight()。类别之程序成员必须与其对象配合使用。格式为﹕
亦即﹐必须以讯息之形式出现。例如﹕
如果程序成员不与对象相配合时﹐计算机会如何处理呢﹖例如﹕
"ex04.bas
"Some Error Here !
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"--------------------------------------------------------------
Class Tree
Public varity As String
Public age As Integer
Public height As Single
Public Sub input(ByVal hei As Single)
height = hei
End Sub
Public Function inquireHeight() As Single
inquireHeight = height
End Function
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 Tree = New Tree()
Dim h As Single
a.input(2.1)
h = inquireHeight()
Messagebox.Show("height = " + str(h) + "公尺", "HI!")
End Sub
End Class
当计算机看到Form1_Click()内之指令──
h = inquireHeight( )
它视inquireHeight()为一独立之程序﹐与Tree类别内之inquireHeight()无关﹔于是计算机去找此inquireHeight()之定义﹐但找不着﹔所以程序错了。因之﹐您要掌握个原则── 程序成员之唯一任务是支持对象之行为﹐必须与对象配合使用。
2. 「封装性」概念
对象把资料及程序组织并「封装」(Encapsulate) 起来﹐只透过特定的方式才能使用类别之资料成员和程序成员。对象如同手提袋﹐只从固定的开口才能存取东西﹐否则您一定不敢把钱放在手提袋中。对象像一座「防火墙」保护类别中的资料﹐使其不受外界之影响。想一想我国的万里长城可保护关内的人民﹐避免受胡人侵犯﹐但长城并非完全封闭﹐而有山海关、玉门关等出入口。对象和万里长城之功能是一致的﹐它保护其资料成员﹐但也有正常的资料存取管道﹕以程序成员来存取资料成员。请看个程序﹕
"ex05.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"-------------------------------------------------------
Class Tree
Public varity As String
Public age As Integer
Public height As Single
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.height = 2.1