|
no As Integer)
SetValue(na, a)
student_number = no
End Sub
Public Sub pr()
MyBase.Display()
Messagebox.Show("StudNo: " + str(student_number))
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 x As New Person()
x.SetValue("Alvin", 32)
Dim y As New Student()
y.SetValue("Tom", 36, 11138)
x.Display()
y.pr()
End Sub
End Class
此程序输出﹕
Name: Alvin Age: 32
Name: Tom Age: 36
StudNo: 11138
此时﹐Student 类别含有name、age 及student_number三个资料成员。而且拥有 SetValue()、Person.SetValue() 、Display()、pr() 及birthYear()五个程序成员。于是建立了如下之继承关系﹕
x 对象含name及age 两项资料﹐指令──x.SetValue ("Alvin", 32)﹐将资料存入x 对象中。因Student继承Person﹐所以y 对象内含name、age 及student_number三项资料﹐指令──y.SetValue("Tom", 36, 11138) 将资料存入y 对象中。上述 SetValue()程序之功能是﹕设定对象之初值。可由建构者(Constructor) 代替之。所以此Student之定义相当于──
''''ex06.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''----------------------------------------------------
Public Class Person
Private name As String
Private age As Integer
Public Sub New()
End Sub
Public Sub SetValue(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
Public Function birthDay() As Integer
birthDay = 2001 - age
End Function
Public Sub Display()
Messagebox.Show("Name: " + name + " Age: " + str(age))
End Sub
End Class
Public Class Teacher
Inherits Person
Private salary As Decimal
Public Overloads Sub SetValue(ByVal na As String, ByVal a As Integer, ByVal sa As Decimal)
SetValue(na, a)
salary = sa
End Sub
Public Sub pr()
MyBase.Display()
Messagebox.Show("Salary: " + str(salary))
End Sub
End Class
Public Class Student
Inherits Person
Private student_number As Integer
Public Sub New(ByVal na As String, ByVal a As Integer, ByVal no As Integer)
SetValue(na, a)
student_number = no
End Sub
Public Sub pr()
MyBase.Display()
Messagebox.Show("StudNo: " + str(student_number))
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 x As New Person()
x.SetValue("Alvin", 32)
Dim y As New Student("Tom", 36, 11138)
x.Display()
y.pr()
End Sub
End Class
此程序输出﹕
Name: Alvin Age: 32
Name: Tom Age: 36
StudNo: 11138
子类别之建构者呼叫父类别之SetValue()来设定对象初值。请仔细看y 对象之诞生过程﹕y 诞生时﹐建构者──
Public Sub New(ByVal na As String, ByVal a As Integer, ByVal no As Integer)
SetValue(na, a)
student_number = no
End Sub
它先呼叫父类别的自然建构者Person.New()一起诞生y 对象。此时﹐Person.New()诞生如下﹕
继承部分是Person.New()诞生的。Person.New()任务完成了﹐轮到Student的建构者本身诞生（扩充）如下﹕
诞生完毕﹐开始执行Student建构者内之指令以设定y 之初值。首先呼叫父类别的SetValue() ﹐于是SetValue()将值存入y 如下﹕
最后﹐执行指令── student_number = no﹐设定student_number数据之初值﹕
于是﹐Student的建构者诞生y 对象﹐也设定初值﹐功成圆满。
上述的Student建构者呼叫父类别之自然建构者（因为Person类别未定义建构者﹐计算机自动产生自然建构者）来协助诞生对象。如果Person类别定义了建构者﹐Student建构者便能直接呼叫Person建构者了。例如﹕
''''ex07.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''-----------------------------------------------------------------------------------------
Public Class Person
Private name As String
Private age As Integer
Public Sub New(ByVal na As String, ByVal a As Integer)
name = na
age = a
End Sub
Public Function birthDay() As Integer
birthDay = 2001 - age
End Function
Public Sub Display()
Messagebox.Show("Name: " + name + " Age: " + str(age))
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