关于子类与父类.
public class Ractangle {
        private double width;
        public double height;
        public double Width {
            set {
                if (0 < value) {
                    this.width = value;
                }
                else {
                    this.width = value;
                }
            }
            get {
                return this.width;
            }
        }
        public double Height {
            set {
                if (0 < value) {
                    this.height = value;
                }
                else {
                    this.height = -1;
                }
            }
            get {
                return this.Height;
            }
        }
        public Ractangle(double w, double h) {
            if (0 < w && 0 < h) {
                this.width = w;
                this.height = h;
            }
        }
    }
//这里报错:Page180Ex04.Ractangle' does not contain a constructor that takes 0 arguments
    public class ExRactangle:Ractangle {
        public ExRactangle(double&