class Shape
    {
        public virtual void Draw()
        {
            Console.WriteLine("Draw a shape");
        }
    }
    class Circle : Shape
    {
        public override void Draw()
        {
            Console.WriteLine("Draw a circle");
        }
    }
    class Rectangle : Shape
    {
        public override void Draw()
        {
            Console.WriteLine("Draw a Rectangle");
        }
    }
    class Triangle : Shape
    {
        public override void Draw()
        {
            Console.WriteLine("Draw a Triangle");
        }
    }
    class Programm
    {
        static void Main()
        {
            //此次就說明了，派生類對象可以作為基類對象進行處理
            Shape[] shapes =
            {
             new Circle(),
             new Rectangle(),
             new Triangle()
            };

            foreach (Shape s in shapes)
            {
                //調用Draw()方法的時候,調用了派生重寫的方法，而不是基類
                s.Draw();
            }
        }
    }