onResponse凌空范围之外的空列表

Question

我有一个静态列表列表，当尝试在onResponse排球方法中从服务器填充此列表时，它可以工作，但在Response.Listener范围之外，列表变为空

public class MapsFragment extends Fragment implements OnMapReadyCallback {

static List<Train> trainsListe = new ArrayList<>();

@Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        MapFragment fragment = (MapFragment) getChildFragmentManager().findFragmentById(R.id.map);
        fragment.getMapAsync(this);

public void parseRedis() {
            StringRequest stringRequest = new StringRequest(uri2,
                    new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {


                        List<Train> listeTemporaire = TrainRedisJsonParser.parseData(response);
                        for (Train t : listeTemporaire)
                        MapsFragment.trainsListe.add(t);
                        System.out.println(trainsListe.size()); // size is 4 here (it works)

                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // Toast.makeText(getActivity(),error.getMessage(),Toast.LENGTH_LONG).show();

                    }
                });

        RequestQueue requestQueue = Volley.newRequestQueue(getActivity());
        requestQueue.add(stringRequest);
    }

parseRedis();
System.out.println(MapsFragment.trainsListe.size()) // 0
}

但是在方法之外，例如在onViewCreated的某处，当我尝试打印trainListe的大小时：0