C#：继承多态的方法实现数的简单加减乘除运算

   // 定义一个抽象的父类

    abstract class Figure

    {

        //声明抽象方法：

        //父类中的所有家里人可以用的方法必须都应用到子类中

        abstract public object getValue();//或者用virtual但是后面必须声明主体部分{ return null; }

        abstract public Figure Add(Figure f1); //{ return null; }

        abstract public Figure Sub(Figure f1);

        abstract public Figure Mul(Figure f1);

        abstract public Figure Div(Figure f1);

    }

    // 实数子类

    class DoubleFigure : Figure

    {

        //声明一个double型字段来存放数据

        protected double _myDouble;

        //运行的时候调用实现初始化

        public DoubleFigure(double num1)

        {

            this._myDouble = num1;

        }

        // 重写父类中输出结果的方法

        public override object getValue()

        {

            return _myDouble;

        }

        //实数相加

        public override Figure Add(Figure f1)

        {

            double doublenum = (double)this.getValue() + (double)f1.getValue();

            //f1.getValue()实际执行的结果类型不由f1声明时的类型决定，而是由指向堆中的内容决定

            DoubleFigure df = new DoubleFigure(doublenum);

            return df;//这里返回值类型为什么不是Figure也可以

            //在堆中开辟的空间地址传给了父类中的变量------父类的变量指向子类中的实例

            //父类变量能传递给子类中变量是因为实际类型没有改变

        }

        //这里不能用运算符的重载：operator必须和public static一同使用，而override不能与static同用

        //public override Figure operator +(DoubleFigure f1)

        //{

        //    double doubleNum = (double)this.getValue() + (double)f1.getValue();

        //    DoubleFigure df = new DoubleFigure(doubleNum);

        //    return df;      

        //}

        // 实数相减

        public override Figure Sub(Figure f1)

        {

            double doubleNum = (double)this.getValue() - (double)f1.getValue();

            DoubleFigure df = new DoubleFigure(doubleNum);

            return df;

        }

        // 实数相乘

        public override Figure Mul(Figure f1)

        {

            double doubleNum = (double)this.getValue() * (double)f1.getValue();

            DoubleFigure df = new DoubleFigure(doubleNum);

            return df;

        }

        //实数相除

        public override Figure Div(Figure f1)

        {

            if ((double)f1.getValue()!=0)

            {

double doubleNum = (double)this.getValue() / (double)f1.getValue();

                DoubleFigure df = new DoubleFigure(doubleNum);   

                return df;         

            }  

            else

            {

                Console.WriteLine("除数不能为0！");

                return new DoubleFigure(0);

            }

        }

        //隐式转换方法实现DoubleFigure类型的数隐式转换为int型

        public static  implicit operator DoubleFigure(int myInt1)

        {

            return new DoubleFigure(myInt1);

        }

       static void Main(string[] args)

        {

            //父类的变量指向子类的实例

            Figure f1 = new DoubleFigure(6);//整数实例

            Figure f2 = new DoubleFigure(1.2); //实数实例

            DoubleFigure f3 = (DoubleFigure)f1.Div(f2);

            Console.WriteLine(f3.getValue()); 

            Console.ReadKey();

        }