@Override public boolean hasNext() throws IOException, CollectionException {
  if (nodes.isEmpty()) {
    if (fileIterator.hasNext()) {
      processNextFile();
    }
 else {
      return false;
    }
  }
  return true;
}

@ Override public boolean hasNext ( ) throws IOException , CollectionException { if ( nodes . isEmpty ( ) ) { if ( fileIterator . hasNext ( ) ) { processNextFile ( ) ; } else { return false ; } } return true ; }
check whether there is still nodes to be processed . < p > after all nodes from current file get processed , read in nodes from the next file
