class DownloadListenerBunch implements DownloadListener {

    public int indexOf(DownloadListener targetListener) {
        for (int index = 0; index < listenerList.length; index++) {
            final DownloadListener listener = listenerList[index];
            if (listener == targetListener) return index;
        }

        return -1;
    }

      DownloadListenerBunch(@NonNull DownloadListener[] listenerList);

}