一份有趣的代码

using System;class A{    public A()    {        PrintFields();    }    public virtual void PrintFields() { }}class B : A{    int x = 1;    int y;    public B()    {        y = -1;    }    public override void PrintFields()    {        Console.WriteLine("x={0},y={1}", x, y);    }}class Test{    public static void Main()    {        new B();    }}