private static void refreshFriends(boolean firstStart) {
        GraphRequest request = GraphRequest.newMyFriendsRequest(accessToken, new GraphRequest.GraphJSONArrayCallback() {
            @Override
            public void onCompleted(JSONArray jsonArray, GraphResponse graphResponse) {
                // request successfully returned
                if (graphResponse.getError() == null) {
                    Log.d("response length: ", Integer.toString(jsonArray.length()));
                    Set<Friend> friends = new TreeSet<>(new Friend.NameComparator());
                    for(int i = 0; i < jsonArray.length(); i++) {
                        try {
                            JSONObject user = jsonArray.getJSONObject(i);
                            String name = user.getString("name");
                            String id = user.getString("id");
                            String imageUrl = user.getString("picture");
                            Friend friend = new Friend(Long.parseLong(id), name, imageUrl);
                            friends.add(friend);
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                    if (firstStart) {
                        friendListListener.onFirstAppStart(friends);
                    } else {
                        friendListListener.onAppStart(friends);
                    }
                }
            }
        });

        Bundle parameters = new Bundle();
        parameters.putString("fields", "id,name,picture");
        request.setParameters(parameters);
        request.executeAsync();
}