boolean add(DownloadRequest request){
  if (query(request.downloadId()) != DownloadState.INVALID || query(request.uri()) != DownloadState.INVALID) {
    Log.w(TAG,"the download requst is in downloading");
    return false;
  }
  request.setDownloadRequestQueue(this);
synchronized (currentRequests) {
    currentRequests.add(request);
  }
  downloadQueue.add(request);
  return true;
}

boolean add ( DownloadRequest request ) { if ( query ( request . downloadId ( ) ) != DownloadState . INVALID || query ( request . uri ( ) ) != DownloadState . INVALID ) { Log . w ( TAG , "the download requst is in downloading" ) ; return false ; } request . setDownloadRequestQueue ( this ) ; synchronized ( currentRequests ) { currentRequests . add ( request ) ; } downloadQueue . add ( request ) ; return true ; }
add download request to the download request queue .
