Android : Using GPS on Services

On this code i want to get the gps location every 3 seconds. but when i run this program on my device it tells me that latitude and longitude are both 0 every time. how should i handle this problem? and what is the looper task ?? it gives me error when i donot use it

public class LocationService extends Service  {

final static String TAG = "MyService";
double latitude ;
double Longitude ;
LocationManager lm;
LocationListener ll;

@Override
public IBinder onBind(Intent intent) {
    return null;
}

@Override
public void onCreate() {

    Log.d(TAG, "onCreate");
    super.onCreate();
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
                    new Thread() {
                    public void run() {
                    Looper.prepare();
                    while(true){
                    lm = (LocationManager) getSystemService(LOCATION_SERVICE);
                    ll = new MyLocationListener();

                    lm.requestLocationUpdates(LocationManager.GPS_PROVIDER,
                    0, 0, ll);       
               //when i log here , it gives me wronganswer                          
               Log.d(TAG,Double.toString(latitude));
                    try {
                        Thread.sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                        }
                        }
                    }
                }.start();
                    return super.onStartCommand(intent, flags, startId);
}
@Override
public void onDestroy() {
    Log.d(TAG, "OnDestroy");
    super.onDestroy();
}

class MyLocationListener implements LocationListener{
        @Override
        public void onLocationChanged(Location location) {
            //when i log here , it gives me correct answer
            double lat = location.getLatitude();
            double lon = location.getLongitude();
            latitude = lat;
            Longitude = lon;
        }
        @Override
        public void onProviderDisabled(String arg0) {
        }

        @Override
        public void onProviderEnabled(String arg0) {
        }

        @Override
        public void onStatusChanged(String arg0, int arg1, Bundle arg2) {
        }
 };
}