NM的C++，基类指针指向派生类时指针概念已经与C语言的有很大不同，但你还用“->” - Chinaunix

public class Shape
{
// A few example members
public int X { get; private set; }
public int Y { get; private set; }
public int Height { get; set; }
public int Width { get; set; }
// Virtual method
public virtual void Draw()
{
Console.WriteLine("Performing base class drawing tasks");
}
}
class Circle : Shape
{
public override void Draw()
{
// Code to draw a circle...
Console.WriteLine("Drawing a circle");
base.Draw();
}
}
class Rectangle : Shape
{
public override void Draw()
{
// Code to draw a rectangle...
Console.WriteLine("Drawing a rectangle");
base.Draw();
}
}
class Triangle : Shape
{
public override void Draw()
{
// Code to draw a triangle...
Console.WriteLine("Drawing a triangle");
base.Draw();
}
}
class Program
{
static void Main(string[] args)
{
// Polymorphism at work #1: a Rectangle, Triangle and Circle
// can all be used whereever a Shape is expected. No cast is
// required because an implicit conversion exists from a derived
// class to its base class.
System.Collections.Generic.List<Shape> shapes = new System.Collections.Generic.List<Shape>();
shapes.Add(new Rectangle());
shapes.Add(new Triangle());
shapes.Add(new Circle());
// Polymorphism at work #2: the virtual method Draw is
// invoked on each of the derived classes, not the base class.
foreach (Shape s in shapes)
{
s.Draw();
}
// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
/* Output:
Drawing a rectangle
Performing base class drawing tasks
Drawing a triangle
Performing base class drawing tasks
Drawing a circle
Performing base class drawing tasks
*/

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public class Shape
{
// A few example members
public int X { get; private set; }
public int Y { get; private set; }
public int Height { get; set; }
public int Width { get; set; }
}
Interface ShapeMethods
{
public void Draw();
}
public class Circle : Extends Shape Implments ShapeMethods
{
public void Draw()
{
// Code to draw a circle...
Console.WriteLine("Drawing a circle");
base.Draw();
}
}
...

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