类的构造方法（函数）(课本5.2)（相关vb.net教程)
1、构造方法是名称是new的过程，前面要以public说明。
2、同时可以定义多个同名的构造方法，只要它的参数个数或类型不同，此时称为重载。以增加构造方法的适用范围。
3、构造方法只在创建对象时由系统调用，不能在程序中人为调用。
修改上面“我的日期类”类，得到程序：类的构造方法，程序为：
Public Class mydate
    Public m_year, m_month, m_day As Integer
    Public Sub New()
        m_year = Microsoft.VisualBasic.Year(Now)
        m_month = Microsoft.VisualBasic.Month(Now)
        m_day = Microsoft.VisualBasic.Day(Now)
    End Sub
    Public Sub New(ByVal y As Integer, ByVal m As Integer, ByVal d As Integer)
        m_year = y : m_month = m : m_day = d
    End Sub
    Public Sub show()
        MsgBox(Str(m_year) + "-" + Str(m_month) + "-" + Str(m_day), MsgBoxStyle.OkOnly, "日期")
    End Sub
End Class
 
Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim a As New mydate
        Dim b As New mydate(2008, 5, 1)
        a.show()
        b.show()
    End Sub
End Class
应用实例：用定义类的方法编程解决，任输入矩形的两边，求其周长与面积。
见，类的应用矩形问题，程序为：
Public Class juxing
    Public x, y As Integer
    Public Function p()
        p = 2 * (x + y)
    End Function
    Public Function area()
        area = x * y
    End Function
End Class
Public Class Form1
    Dim a As New juxing
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim pp, ss As Double
        pp = a.p
        ss = a.area
        Console.WriteLine("周长为：" + Str(pp))
        Console.WriteLine("面积为：" + Str(ss))
    End Sub
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        a.x = Val(TextBox1.Text)
        a.y = Val(TextBox2.Text)
    End Sub
End Class