I have asked this question preivously on Physics site of Stack Exchange Link but since got little attention and suggestion I am posting this question here.

I am trying to make a simple java program to do planetary orbital calculation like how many days it takes to complete the orbital along with each Earth day data but I end up getting a 4 days error. Can anybody explain why?

After fixing some problems after @PM2Ring's comment on Link

I have this code

        double semiMajorAxis = 1.5237 * 149598000;
        double eccentricty = 0.0934;
        double current_time = 0;
        double last_speed;
        double angular_distance = 0; // unit : rad
        boolean stop = false;
        double last_day_distance = 0;
        double avg_speed = 0;
        double distance_in_km;
        double last_day_angular_distance = 0;
        while (!stop) {
            double radius = get_radius(angular_distance, eccentricty, semiMajorAxis);
            last_speed = (get_speed(radius * 1000) / radius);
            angular_distance += last_speed;
            distance_in_km = angular_distance * radius;
            current_time += 1;
            
            if (angular_distance >= Math.PI * 2) {
                System.out.println("Total days : " + current_time / 60 / 60 / 24);
                stop = true;
            }
           }

Functions used in the above program-

   public static double get_radius(double theeta, double eccentricty, double a) {
        // modern kepler formula
        return a * (1 - Math.pow(eccentricty, 2)) / (1 + eccentricty * Math.cos(theeta));
    }

    public static double get_speed(double r, double semiMajorAxis) {
        double mu = 1.32712440042 * Math.pow(10, 20);
        // vis-viva equation
        return (Math.sqrt(mu * ((2 / r) - (1 / semiMajorAxis))) / 1000);
    }

What am I trying to do? - I am trying to calculate time taken for each planet to complete its revolution and also collect daily data for it, in this case its the Mars. To do this I am using 1 second step to calculate angles displaced by using vis-viva to calculate speed and kepler formula to get radius.

However seems like there is a problem as the output I am getting for Mars is 685.4825000000001 days which is nearly 2 days behind of actual time i.e 687 days and for Jupiter I am getting 4334.061006944444 days which is nearly 2 day ahead of actual time 4332 days.

Can anybody help me fix the error or could guide me with some other way. It will really be helpfull.