範例一：矩形、圓形繼承形狀 (Shape)

using System;
class Shape
{
    public virtual double area() { return 0.0; }
}
class Rectangle : Shape
{
    double width, height;
    public Rectangle(double w, double h)
    {
        width = w;
        height = h;
    }
    public override double area()
    {
        return width * height;
    }
}
class Circle : Shape
{
    double r;
    public Circle(double r)
    {
        this.r = r;
    }
    public override double area()
    {
        return 3.1416 * r * r;
    }
}
class Test
{
    public static void Main(string[] args)
    {
        Shape s = new Shape();
        Console.WriteLine("s.area() = " + s.area());
        Rectangle r = new Rectangle(5.0, 8.0);
        Console.WriteLine("r.area() = " + r.area());
        Circle c = new Circle(2);
        Console.WriteLine("c.area() = " + c.area());
    }
}

執行結果： 

s.area() = 0
r.area() = 40
c.area() = 12.5664

範例二：加入厚度與體積函數 (在子物件使用父物件的欄位)

執行結果 

s.area() = 0
r.area() = 40
r.volume() = 80
c.area() = 12.5664
c.volume() = 37.6992
c.volume() = 62.832

程式碼 

using System;
class Shape
{
    public double thick;
    public virtual double area() { return 0.0; }
}
class Rectangle : Shape
{
    double width, height;
    public Rectangle(double w, double h)
    {
        width = w;
        height = h;
        thick = 2.0;
    }
    public override double area()
    {
        return width * height;
    }
    public double volume()
    {
        return width * height * thick;
    }
}
class Circle : Shape
{
    double r;
    public Circle(double r)
    {
        this.r = r;
        thick = 3.0;
    }
    public override double area()
    {
        return 3.1416 * r * r;
    }
    public double volume()
    {
        return area() * thick;
    }
}
class Test
{
    public static void Main(string[] args)
    {
        Shape s = new Shape();
        Console.WriteLine("s.area() = " + s.area());
        Rectangle r = new Rectangle(5.0, 8.0);
        Console.WriteLine("r.area() = " + r.area());
        Console.WriteLine("r.volume() = " + r.volume());
        Circle c = new Circle(2);
        Console.WriteLine("c.area() = " + c.area());
        Console.WriteLine("c.volume() = " + c.volume());
        c.thick = 5;
        Console.WriteLine("c.volume() = " + c.volume());
    }
}

範例三：將 volume() 函數提到 Shape 物件中

using System;
class Shape
{
    public double thick;
    public virtual double area() { return 0.0; }
    public double volume()
    {
        return area() * thick;
    }
}
class Rectangle : Shape
{
    double width, height;
    public Rectangle(double w, double h)
    {
        width = w;
        height = h;
        thick = 2.0;
    }
    public override double area()
    {
        return width * height;
    }
}
class Circle : Shape
{
    double r;
    public Circle(double r)
    {
        this.r = r;
        thick = 3.0;
    }
    public override double area()
    {
        return 3.1416 * r * r;
    }
}
class Test
{
    public static void Main(string[] args)
    {
        Shape s = new Shape();
        Console.WriteLine("s.area() = " + s.area());
        Rectangle r = new Rectangle(5.0, 8.0);
        Console.WriteLine("r.area() = " + r.area());
        Console.WriteLine("r.volume() = " + r.volume());
        Circle c = new Circle(2);
        Console.WriteLine("c.area() = " + c.area());
        Console.WriteLine("c.volume() = " + c.volume());
        c.thick = 5;
        Console.WriteLine("c.volume() = " + c.volume());
    }
}

文章轉載：陳鍾誠 (2010年10月19日)，(網頁標題) C# 與物件導向的繼承 (Inheritance)，(網站標題) 免費電子書：C# 程式設計，2010年10月19日，取自 http://cs0.wikidot.com/inheritance ，網頁修改第 5 版。

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