1     //基类 
2     abstract class Shape
3     {
4         //抽象方法 计算面积
5         public abstract double ComputerArea();
6 
7     }

//子类 继承Shape 实现抽象方法
    class Circle : Shape
    {
        private double _radius;

        //构造函数
        public Circle(double radius) => _radius = radius;

        //实现抽象方法
        public override double ComputerArea()
        {
            return _radius * _radius * Math.PI;
        }
    }

    //子类 继承Shape 实现抽象方法
    class Rectangle : Shape
    {

        private double _width;

        private double _height;

        //构造函数
        public Rectangle(double width, double height)
        {
            _width = width;
            _height = height;
        }
        //实现抽象方法
        public override double ComputerArea()
        {
            return _width * _height;
        }
    }

    //子类 继承Shape 实现抽象方法
    class Triangle : Shape
    {

        private double _bottom;

        private double _height;

        //构造函数
        public Triangle(double bottom, double height)
        {
            _bottom = bottom;
            _height = height;
        }
        //实现抽象方法
        public override double ComputerArea()
        {
            return _bottom * _height / 2;
        }
    }

 1 //计算类
 2     class Calculate
 3     {
 4         //传入一个父类作为参数，调用方法
 5         public void Calc(Shape shape)
 6         {
 7 
 8             Console.WriteLine($"{shape.GetType().Name}的面积:{shape.ComputerArea()}");
 9         }
10     }

class Program
    {
        static void Main(string[] args)
        {
            var circle = new Circle(5);
            var rect = new Rectangle(5, 10);
            var triangle = new Triangle(6, 8);

            var calc = new Calculate();

            calc.Calc(circle);
            calc.Calc(rect);
            calc.Calc(triangle);
        }
    }