Calculating distance between two points, using latitude and longitude

Distance Calculator

/**
 * Created by hani on 12/6/16.
 */

public class DistanceCalculator {
    public String distance(double lat1, double lon1, double lat2, double lon2) {
        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;
        dist = dist * 1.609344;

        if (dist == 0)
            return "";
        else if (dist < 1)
            return String.format("%s m", (int) (dist * 1000));
        else return String.format("%s km", round(dist, 1));
    }

    private double round(double value, int precision) {
        int scale = (int) Math.pow(10, precision);
        return (double) Math.round(value * scale) / scale;
    }

    private double deg2rad(double deg) {
        return (deg * Math.PI / 180.0);
    }

    private double rad2deg(double rad) {
        return (rad * 180 / Math.PI);
    }
}

============================================
==========Distance Calculator Test==========
============================================

/**
 * Created by hani on 12/6/16.
 */

public class DistanceCalculatorTest {
    @Test
    public void distance_kilometer() {
        DistanceCalculator distanceCalculator = new DistanceCalculator();
        String distance = distanceCalculator.distance(35.689197, 51.388974, 34.639944, 50.875942);

        Assert.assertEquals("125.6 km", distance);
    }

    @Test
    public void distance_kilometer_meter() {
        DistanceCalculator distanceCalculator = new DistanceCalculator();
        String distance = distanceCalculator.distance(38.898556, 77.037852, 38.897147, 77.043934);

        Assert.assertEquals("549 m", distance);
    }

    @Test
    public void distance_equal() {
        DistanceCalculator distanceCalculator = new DistanceCalculator();
        String distance = distanceCalculator.distance(35.689197, 51.388974, 35.689197, 51.388974);

        Assert.assertEquals("", distance);
    }
}