code: public int getDocFreq(int term) {
  		int[] docfreq = (int[]) this.index2docfreq.get(Integer.valueOf(term));
  		if (docfreq == null)
  			return 0;
  		return docfreq[0];
  	}
docs: *************************************************************************
  Returns the document frequency of a term in the collection or 0 if the
  term is unknown or has been filtered
  ************************************************************************