java - Finding all values within a radius using geographical math -

how can find values (in case establishments) within radius of (x) miles using latitude/longitude coordinates?

the code:

public class geogen {      static final geoposition user_position = new geoposition(39.410868, -107.102182);      public static void main(string[] args) {         new establishment("fries electronics", randomlocation(user_position, 40)).print();         new establishment("walmart supercenter", randomlocation(user_position, 40)).print();         new establishment("target", randomlocation(user_position, 40)).print();         new establishment("krogers", randomlocation(user_position, 40)).print();         new establishment("mcdonalds", randomlocation(user_position, 40)).print();     }      public static geoposition randomlocation(geoposition location, double radius) {         random random = new random();          // convert radius miles meters         double meters = radius * 1609.34;          // convert radius meters degrees         double radiusindegrees = meters / 111000f;          double u = random.nextdouble();         double v = random.nextdouble();         double w = radiusindegrees * math.sqrt(u);         double t = 2 * math.pi * v;         double x = w * math.cos(t);         double y = w * math.sin(t);          // adjust x-coordinate shrinking of east-west distances         double new_x = x / math.cos(location.latitude());          double foundlongitude = new_x + location.longitude();         double foundlatitude = y + location.latitude();         return new geoposition(foundlongitude, foundlatitude);     }      public static double distancebetween(geoposition a, geoposition b) {         double longdif = a.longitude() - b.longitude();          double distance =                  math.sin(deg2rad(a.latitude()))                 *                 math.sin(deg2rad(b.latitude()))                 +                 math.cos(deg2rad(a.latitude()))                 *                 math.cos(deg2rad(b.latitude()))                 *                 math.cos(deg2rad(longdif));         distance = math.acos(distance);         distance = rad2deg(distance);         distance = distance * 60 * 1.1515; // convert meters         distance = distance * 0.8684; // convert miles.         return distance;     }      private static double rad2deg(double rad) {         return (rad * 180.0 / math.pi);     }      private static double deg2rad(double deg) {         return (deg * math.pi / 180.0);     }  }  /**  * class representing establishment in world.  *   * @author christian  */ class establishment {      public static map<geoposition, string> establishments = new hashmap<>();      private final string name;     private final geoposition geoposition;      public establishment(string name, geoposition geoposition) {         this.name = name;         this.geoposition = geoposition;         establishments.put(geoposition, name);     }      public void print() {         system.out.print("establishment("+name+") created approx ");         system.out.printf("%.2f", geogen.distancebetween(geoposition, geogen.user_position));         system.out.print(" miles specified lat/long \n");     }      public final string name() { return name; }     public final geoposition position() { return geoposition; } }  /**  * class representing geographical location using latitude/longitude.  *   * @author christian  */ class geoposition {     private final double longitude;     private final double latitude;      public geoposition(double longitude, double latitude) {         this.longitude = longitude;         this.latitude = latitude;     }      public double longitude() { return longitude; }     public double latitude() { return latitude; } } 

running application produce different results each time, it's randomized, here example of using geogen#distancebetween(geoposition, geoposition) method.

establishment(fries electronics) created approx 19.26 miles specified lat/long  establishment(walmart supercenter) created approx 9.79 miles specified lat/long  establishment(target) created approx 28.83 miles specified lat/long  establishment(krogers) created approx 10.61 miles specified lat/long  establishment(mcdonalds) created approx 3.37 miles specified lat/long  

however, i'm trying figure out how establishments within x miles. example this

geogen#findestablishmentswithinradius(geoposition, double) returns list<establishment> 

which return list of establishments within x miles of specified geoposition.

you have method calculate distance? loop through establishments , check if within radius or not.

add of establishments list, , can use stream example:

public list<establishment> findestablishmentswithinradius(list<establishment> list, geoposition position, double radius) {     return list.stream().filter(e -> distancebetween(position, e.position()) <= radius).collect(collectors.tolist()); }