سوال در مورد ArrayList و خطا ؟

 image.setImageResource(imageIds.get(position).thumbnail);

 public class StructureImage {

    public String title;
    public String thumbnail;
    public String url;
}

 public class ActivityStartup extends Activity {

    public PagerAdapter adapter;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        getImageListFromServer();
        final PageIndicator indicator = (PageIndicator) findViewById(R.id.indicator);
        ArrayList<StructureImage> images = new ArrayList<StructureImage>();
        ArrayList<StructureImage> imageTitles = new ArrayList<StructureImage>();
        ViewPager pager = (ViewPager) findViewById(R.id.pager);
        ImagePagerAdapter adapter = new ImagePagerAdapter(images, imageTitles);
        pager.setAdapter(adapter);
        pager.setOnPageChangeListener(new OnPageChangeListener() {

            @Override
            public void onPageSelected(int index) {}


            @Override
            public void onPageScrolled(int startIndex, float percent, int pixel) {
                indicator.setPercent(percent);
                Log.i("LOG", "Percent: " + startIndex + ", " + percent);
                indicator.setCurrentPage(startIndex);
            }


            @Override
            public void onPageScrollStateChanged(int arg0) {

            }
        });

    }


    private void getImageListFromServer() {
        String result = Webservice.readUrl("http://id-setak.com/old/note_server/img.php/", null);
        if (result != null) {
            try {
                G.images.clear();
                JSONArray tasks = new JSONArray(result);
                for (int i = 0; i < tasks.length(); i++) {
                    JSONObject object = tasks.getJSONObject(i);
                    StructureImage image = new StructureImage();
                    image.title = object.getString("title");
                    image.thumbnail = object.getString("thumbnail");
                    image.url = object.getString("url");
                    Log.i("LOG", object.getString("thumbnail"));
                    Log.i("LOG", object.getString("title"));

                    //    DownloadManager.addToDownloadList(image.thumbnail);

                    G.images.add(image);
                }

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