distance calculation using zip code in java

Last sunday, i was coding up for an ecommerce website in java. Now, i had a requirement for distance calculation from zip code entered by the user. I googled a lot and found an intresting formulae for distance calculation from zip code.

I have changed it into a java function for flexibility and ease :: See code below ::

private double distance(double lat1, double lon1, double lat2, double lon2, char unit) {
  double theta = lon1 - lon2;
  double dist = Math.sin(deg2rad(lat1)) * Math.sin(deg2rad(lat2)) + Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * Math.cos(deg2rad(theta));
  dist = Math.acos(dist);
  dist = rad2deg(dist);
  dist = dist * 60 * 1.1515;
  if (unit == "K") {
    dist = dist * 1.609344;
  } else if (unit == "N") {
   dist = dist * 0.8684;
    }
  return (dist);
}

/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
/*::  This function converts decimal degrees to radians             :*/
/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
private double deg2rad(double deg) {
  return (deg * Math.PI / 180.0);
}

/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
/*::  This function converts radians to decimal degrees             :*/
/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
private double rad2deg(double rad) {
  return (rad * 180.0 / Math.PI);
}

system.println(distance(32.9697, -96.80322, 29.46786, -98.53506, "M") + " Miles\n");
system.println(distance(32.9697, -96.80322, 29.46786, -98.53506, "K") + " Kilometers\n");
system.println(distance(32.9697, -96.80322, 29.46786, -98.53506, "N") + " Nautical Miles\n");

And it worked great for me !!!

:)