JSON array get length

I can't get the array length of the JSON array. when I using length(); method it is not working, it show as red underline in Netbeans

this is the source code

 try {

        JSONObject myjson = JSONObject.fromObject(practiceInfoByUsername);

        //JSONArray nameArray = myjson.names();
        final JSONArray jar = myjson.getJSONArray("_types");
        for(int i=0; i<jar.length(); i++)
        {
            String p = jar.getString(i);
            Log.i("p",p);


        }

    } catch (JSONException e) {
            e.printStackTrace();
    }