public String toString() {
            StringBuilder s = new StringBuilder();
                for (Planet p : planets) {
                        // We can't use String.format here because in certain locales, the ,
                        // and . get switched for X and Y (yet just appending them using the
                        // default toString methods apparently doesn't switch them?)
                        s.append("P " + p.X() + " " + p.Y() + " " + p.Owner() + " " + p.NumShips() + " " + p.GrowthRate() + "\n");

                }
                return s.toString();
    }