android – How can I get the distance between two point by latlng?-ThrowExceptions

Exception or error:

I want to get the distance from A to B by latlng.When i run my app with the following code,it return a wrong result.
Fx i tryed A( 31.172740,115.0081630) ,then B(30.6055980,114.3603140),the result is about 3111km.but the right distance is about 134km.
My code is:

    class btnListener implements OnClickListener{

    public void onClick(View v) {
         lat_a=lat_A.getText().toString();
         lng_a=lng_A.getText().toString();
         lat_b=lat_B.getText().toString();
         lng_b=lng_B.getText().toString();
         double a1,n1,a2,n2;
         a1=30.6055980;
         a2=Double.parseDouble(lat_b);
         n2=Double.parseDouble(lng_b);
         double R=6371;
         double D=Math.acos(Math.sin(a1)*Math.sin(a2)+Math.cos(a1)*Math.cos(a2)*Math.cos(n2-n1));
         Toast.makeText(getApplication(), "the distance is"+String.valueOf(D*R)+"km from A to B", Toast.LENGTH_SHORT).show();
    }

}
How to solve:

Try below code.

public float distance (float lat_a, float lng_a, float lat_b, float lng_b ) 
{
    double earthRadius = 3958.75;
    double latDiff = Math.toRadians(lat_b-lat_a);
    double lngDiff = Math.toRadians(lng_b-lng_a);
    double a = Math.sin(latDiff /2) * Math.sin(latDiff /2) +
    Math.cos(Math.toRadians(lat_a)) * Math.cos(Math.toRadians(lat_b)) *
    Math.sin(lngDiff /2) * Math.sin(lngDiff /2);
    double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    double distance = earthRadius * c;

    int meterConversion = 1609;

    return new Float(distance * meterConversion).floatValue();
}

If you didn’t understood, please check this link, same code available here.

###

There is an api provided by android itself to get distance between two points. Use:

Location.distanceBetween(
    startLatitude,
    startLongitude,
    endLatitude,
    endLongitude,
    results);

which returns distance in meters.

###

LatLng startLatLng = new LatLng(startLatitude, startLongitude);
LatLng endLatLng = new LatLng(endLatitude, endLongitude)
double distance = SphericalUtil.computeDistanceBetween(startLatLng, endLatLng);

also add

compile 'com.google.android.gms:play-services-maps:15.0.1'
compile 'com.google.maps.android:android-maps-utils:0.5+'

to your gradle dependencies

Distance in meters

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