Android Studio notification on location changed Service

Question

I made an app that suggests nearest Hospitals and Police Stations using Google API.

Now I want to make a new feature: to get notifications when i enter a new city. I know i have to create a Service (my app should work in background) and implement the functionality there. I have found how to get location updates in background here(Get GPS location via a service in Android).

I don't know what to modify to get notifications when I change location too (Like: You are now in city B) and how to call this new feature in MainActivity class

this is my sendMessage() mehtod (for notifications):

//notifications
    public void sendMessage (String message , Intent  intent){

        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 , intent,
                PendingIntent.FLAG_ONE_SHOT);


        String channelId = "some_channel_id";
        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder notificationBuilder =
                new NotificationCompat.Builder(this, channelId)
                        .setSmallIcon(R.mipmap.ic_launcher_round)
                        .setContentTitle(getString(R.string.app_name))
                        .setContentText(message)
                        .setAutoCancel(true)
                        .setSound(defaultSoundUri)
                        .setBadgeIconType(NotificationCompat.BADGE_ICON_SMALL)
                        .setContentIntent(pendingIntent);

        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        // Since android Oreo notification channel is needed.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId,
                    "Channel human readable title",
                    NotificationManager.IMPORTANCE_DEFAULT);
            assert notificationManager != null;
            notificationManager.createNotificationChannel(channel);
        }

        assert notificationManager != null;
        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
    }

also this is the Service I want to modify:

public class LocationService extends Service {
    private static final String TAG = "MyLocationService";
    private LocationManager mLocationManager = null;
    private static final int LOCATION_INTERVAL = 1000;
    private static final float LOCATION_DISTANCE = 10f;

    private class LocationListener implements android.location.LocationListener {
        Location mLastLocation;

        public LocationListener(String provider) {
           // Log.e(TAG, "LocationListener " + provider);
            mLastLocation = new Location(provider);
        }

        @Override
        public void onLocationChanged(Location location) {
            Log.e(TAG, "onLocationChanged: " + location);
            mLastLocation.set(location);
        }

        @Override
        public void onProviderDisabled(String provider) {
          //  Log.e(TAG, "onProviderDisabled: " + provider);
        }

        @Override
        public void onProviderEnabled(String provider) {
           // Log.e(TAG, "onProviderEnabled: " + provider);
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
           // Log.e(TAG, "onStatusChanged: " + provider);
        }
    }

    /*
    LocationListener[] mLocationListeners = new LocationListener[]{
            new LocationListener(LocationManager.GPS_PROVIDER),
            new LocationListener(LocationManager.NETWORK_PROVIDER)
    };
    */

    LocationListener[] mLocationListeners = new LocationListener[]{
            new LocationListener(LocationManager.PASSIVE_PROVIDER)
    };

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        //Log.e(TAG, "onStartCommand");
        super.onStartCommand(intent, flags, startId);
        return START_STICKY;
    }

    @Override
    public void onCreate() {

       // Log.e(TAG, "onCreate");

        initializeLocationManager();

        try {
            mLocationManager.requestLocationUpdates(
                    LocationManager.PASSIVE_PROVIDER,
                    LOCATION_INTERVAL,
                    LOCATION_DISTANCE,
                    mLocationListeners[0]
            );
        } catch (java.lang.SecurityException ex) {
           // Log.i(TAG, "fail to request location update, ignore", ex);
        } catch (IllegalArgumentException ex) {
           // Log.d(TAG, "network provider does not exist, " + ex.getMessage());
        }

        /*try {
            mLocationManager.requestLocationUpdates(
                    LocationManager.GPS_PROVIDER,
                    LOCATION_INTERVAL,
                    LOCATION_DISTANCE,
                    mLocationListeners[1]
            );
        } catch (java.lang.SecurityException ex) {
            Log.i(TAG, "fail to request location update, ignore", ex);
        } catch (IllegalArgumentException ex) {
            Log.d(TAG, "gps provider does not exist " + ex.getMessage());
        }*/
    }

    @Override
    public void onDestroy() {
        //Log.e(TAG, "onDestroy");
        super.onDestroy();
        if (mLocationManager != null) {
            for (int i = 0; i < mLocationListeners.length; i++) {
                try {
                    if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                        return;
                    }
                    mLocationManager.removeUpdates(mLocationListeners[i]);
                } catch (Exception ex) {
                   // Log.i(TAG, "fail to remove location listener, ignore", ex);
                }
            }
        }
    }

    private void initializeLocationManager() {
        Log.e(TAG, "initializeLocationManager - LOCATION_INTERVAL: "+ LOCATION_INTERVAL + " LOCATION_DISTANCE: " + LOCATION_DISTANCE);
        if (mLocationManager == null) {
            mLocationManager = (LocationManager) getApplicationContext().getSystemService(Context.LOCATION_SERVICE);
        }
    }
}