Java 从截取响应后，无法在arraylist中设置值

//这是我计算指定位置和当前位置之间距离的截取方法，在这里我得到了适当的距离。但我不知道为什么距离的值没有在ArrayList中设置

   public void vollyRequest_Fetch_distance(double lat11, double lon11,  double lat22, double lon22,final VolleyCallback callback)

     {
    String url = "https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins="+lat11+","+lon11+"&"+"destinations="+lat22+","+lon22;

    RequestQueue queue = Volley.newRequestQueue(getActivity());

    StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>()
    {
        @Override
        public void onResponse(String response)
        {
            callback.onSuccess(response);

        }
    },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {

                }
            }) {
        @Override
        protected Map<String, String> getParams() {
            Map<String, String> params = new HashMap<String, String>();

            return params;
        }

        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String, String> params = new HashMap<String, String>();
            params.put("key", "KEY");
            return params;
        }
    };
    queue.add(request);

}

salesmanlocation是我的POJO类，我试图在其中设置距离

salesmanlocationArrayList是我的arraylist

 vollyRequest_Fetch_distance(latt, lng1g, lat, lng, new VolleyCallback()
                    {
                        @Override
                        public void onSuccess(String result)
                        {
                             distance=Jsonresponse_Distance(result);
                             Log.d("distance_vol=","val---== "+distance);
                             salesmanlocation.setDistance(distance);
                        }
                    });

//为了调试的目的，我在日志中为空

salesmanlocationArrayList.get（j）.getDistance

for（int j=0；j
salesmanlocation.setDistance();


salesmanlocationArrayList.add(salesmanlocation);

 vollyRequest_Fetch_distance(latt, lng1g, lat, lng, new VolleyCallback()
                    {
                        @Override
                        public void onSuccess(String result)
                        {
                             distance=Jsonresponse_Distance(result);
                             Log.d("distance_vol=","val---== "+distance);
                             salesmanlocation.setDistance(distance);
                        }
                    });

for(int j=0;j<salesmanlocationArrayList.size();j++)
                {
                    Log.d("salesmanarray_list",""+salesmanlocationArrayList.get(j).getDistanc);

                }