As always, you need to make sure you have the required permissions.

public class MainActivity extends AppCompatActivity implements LocationListener{

    private LocationManager mLocationManager = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    }

    @Override
    protected void onResume() {
        super.onResume();

        try {
            mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
        }
        catch(SecurityException e){
            // The app doesn't have the correct permissions
        }
    }

    @Override
    protected void onPause() {
        try{
            mLocationManager.removeUpdates(this);
        }
        catch (SecurityException e){
            // The app doesn't have the correct permissions
        }

        super.onPause();
    }

    @Override
    public void onLocationChanged(Location location) {
        // We received a location update!
        Log.i("onLocationChanged", location.toString());
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }
}