class  Inter {
        public static void main(String[] args) {
                CartesianPoint cp = new CartesianPoint(3, 4);
                System.out.println("cp.x() == " + cp.x());
                System.out.println("cp.y() == " + cp.y());
                System.out.println("cp.r() == " + cp.r());
                System.out.println("cp.theta() == " + cp.theta());

                System.out.println();

                PolarPoint pp = new PolarPoint(5, Math.atan2(4, 3));
                System.out.println("pp.x() == " + pp.x());
                System.out.println("pp.y() == " + pp.y());
                System.out.println("pp.r() == " + pp.r());
                System.out.println("pp.theta() == " + pp.theta());

                System.exit(0);
        }
};

interface Point {
        double x();
        double y();
        double r();
        double theta();
};

class CartesianPoint implements Point {
        private double _x;
        private double _y;

        CartesianPoint(double _x, double _y) {
                this._x = _x;
                this._y = _y;
        }

	@Override
        public double x() {
                return _x;
        }

	@Override
        public double y() {
                return _y;
        }

	@Override
        public double r() {
                return Math.hypot(_x, _y);
        }

	@Override
        public double theta() {
                return Math.atan2(_y, _x);
        }
};

class PolarPoint implements Point {
        private double _r;
        private double _theta;

        PolarPoint(double _r, double _theta) {
                this._r = _r;
                this._theta = _theta;
        }

	@Override
        public double x() {
                return _r * Math.cos(_theta);
        }

	@Override
        public double y() {
                return _r * Math.sin(_theta);
        }

	@Override
        public double r() {
                return _r;
        }

	@Override
        public double theta() {
                return _theta;
        }
};