17、面向对象编程中的继承机制详解

面向对象编程中的继承机制详解

1. 继承的基本概念与使用

1.1 示例类 Sphere

首先，我们来看一个用于表示球体的类 Sphere 。球体有半径和空间位置，在屏幕上显示时会呈现为圆形。以下是 Sphere 类的代码：

Public Class Sphere
    Protected xCoord As Integer = 100, yCoord As Integer = 100
    Protected myPen As Pen = New Pen(Color.Black)
    Public WriteOnly Property X() As Integer
        Set(ByVal value As Integer)
            xCoord = value
        End Set
    End Property
    Public WriteOnly Property Y() As Integer
        Set(ByVal value As Integer)
            yCoord = value
        End Set
    End Property
    Public Overridable Sub Display(ByVal drawArea As Graphics) 
        drawArea.DrawEllipse(myPen, xCoord, yCoord, 20, 20)
    End Sub
End Class

这