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25000、 2及 45000。同时e2含有4 个资料成员──emp_name、salary、counter 及 sum﹔其值分别为"Lily"、20000 、2 及 45000。只是e1之 counter值等于e2之 counter值﹐同时e1之sum 值等于e2之 sum值。
2. 共享程序成员
刚才介绍过共享资料成员(Shared Data Member)之观念。共享资料成员是各对象的公用数据成员﹐但并不属于任何对象﹐而是属于类别的。除了资料成员之外，也有共享程序成员，它是属于类别的﹐而并不属于任何对象﹐其不是用来存取某对象内的值﹐而只储存取共享资料成员之值。任何一般程序成员皆可呼叫共享程序成员来存取共享成员之值。例如﹕
''''ex06.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''----------------------------------------------------------------------
Class Employee
Private emp_name As String
Private salary As Double
Private Shared counter As Integer
Private Shared sum As Double
Shared Sub New()
counter = 0
sum = 0
End Sub
Public Sub New(ByVal na As String, ByVal s As Double)
emp_name = na
salary = s
counter = counter + 1
sum = sum + salary
End Sub
Shared Function NumberOfObject() As Integer
NumberOfObject = counter
End Function
Shared Function Average() As Double
Average = sum / counter
End Function
Public Sub Display()
MessageBox.Show("Name: " + emp_name + " Salary: " + str(salary))
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 e1 As New Employee("Tom", 25000)
Dim e2 As New Employee("Lily", 20000)
MessageBox.Show(str(e1.NumberOfObject()) + " objects")
MessageBox.Show("Avgerage: " + str(e2.Average()))
Dim e3 As New Employee("Linda", 15000)
MessageBox.Show(str(e3.NumberOfObject()) + " objects")
MessageBox.Show("Average: " + str(e3.Average()))
End Sub
End Class
此程序输出：
2 objects
Average: 22500
3 objects
Average: 20000
还记得吗﹖一般程序成员是用来处理对象内的资料﹐所以呼叫一般程序成员之格式为──
对象. 一般程序成员
呼叫这程序成员的目的是来处理此对象之内容。共享程序成员之目的并非在于处理对象之内容﹐而是存取共享资料成员之值或处理些有关于整个类别的事情。因之﹐呼叫共享程序成员的格式为──
类别 . 共享程序成员
呼叫这共享程序成员之目的是来处理此类别之资料或有关之事情。
一种格式──
对象 . 共享程序成员
每个对象皆来自某个类别﹐VB看到对象名称时﹐可对应到它的类别﹐所
以VB在编译这种格式时﹐会将之转换成为﹕
类别 . 共享程序成员
亦即﹐指令── c1.NameOfObject()
及 c2.NameOfObject()
皆会转换成为－－ Employee.NameOfObject()
同理﹐e1.Average()也就相当于Employee.Average() 了。
由上述可知共享程序成员并非处理某个特定的对象值﹐所以没有必要去呼叫一般的程序成员。VB也就禁止共享程序成员呼叫一般的程序成员。不过﹐反之一般程序成员却可以呼叫共享程序成员﹐以便必要时可藉由共享程序成员来取得有关于整个类别的资料。例如：
''''ex07.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''------------------------------------------------------------------------------
Class Employee
Private emp_name As String
Private salary As Double
Private Shared counter As Integer
Private Shared sum As Double
Shared Sub New()
counter = 0
sum = 0
End Sub
Public Sub New(ByVal na As String, ByVal s As Double)
emp_name = na
salary = s
counter = counter + 1
Me.sum = Employee.sum + salary
End Sub
Public Function GetSalary() As Double
GetSalary = salary
End Function
Shared Function NumberOfObject() As Integer
NumberOfObject = counter
End Function
Shared Function Average() As Double
Dim k As Double
Average = Employee.sum / Employee.counter
'''' salary = salary + 2000 '''' Error!
'''' k = GetSalary() '''' Error!
End Function
Public Sub Disp()
MessageBox.Show(str(Employee.NumberOfObject()) + " objects")
MessageBox.Show("Avgerage: " + str(Employee.Average()))
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 e1 As New Employee("Tom", 25000)
Dim e2 As New Employee("Lily", 20000)
e2.disp()
Dim e3 As New Employee("Linda", 15000)
e3.disp()
End Sub
End Class
此程序输出：
2 objects
Average: 22500
3 objects
Average: 20000
共享程序，上述Disp()是一般程序成员，此程序内的指令：
Public Sub Disp()
MessageBox.Show(str(Employee.NumberOfObject()) + " objects")
......
End Sub
这就呼叫了共享的NumberOfObject()程序。
共享程序不可呼叫一般程序，上述Average()是共享程序，它不能呼叫一般程序，所以Average()内的指令有错：
Shared Function Average() As Double
Dim k As Double
Average = Employee.sum / Employee.counter
'''' salary = salary + 2000 '''' Error!
'''' k = GetSalary() '''' Error!
End Function
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