จะหาผลรวมของราคา ใน andriod Listview json ต้องทำอย่างไรบ้างครับ

 try {

            JSONArray data = new JSONArray(getJSONUrl(url,params));

            MyArrList = new ArrayList<HashMap<String, String>>();
            HashMap<String, String> map;
            int SumAmount=0;
            int SumQty=0;
            for(int i = 0; i < data.length(); i++){
                JSONObject c = data.getJSONObject(i);

                map = new HashMap<String, String>();
                map.put("MemberID", c.getString("MemberID"));
                map.put("Username", c.getString("Username2"));
                map.put("Password", c.getString("Password"));
                map.put("Name", c.getString("Name"));
                map.put("Amount", c.getString("Amount"));
                map.put("Qty", c.getString("Qty"));
                SumQty += Integer.parseInt(c.getString("Qty"));
                SumAmount += Integer.parseInt(c.getString("Amount"));
                MyArrList.add(map);



            }

            // แสดงยอดรวม.
            textView.setText(String.valueOf(SumQty));
            textView2.setText(String.valueOf(SumAmount));
            lisView1.setAdapter(new ImageAdapter(this));

        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }