code: public int[] getReferenceNumbers() {
  		Iterator it = m_tunes.keySet().iterator();
  		int[] refNb = new int[m_tunes.size()];
  		int index = 0;
  		while (it.hasNext()) {
  			refNb[index] = (Integer) it.next();
  			index++;
  		}
  		return refNb;
  	}
docs: Returns the reference numbers of tunes contained in this tunebook.
  
  @return An array containing the reference numbers of tunes contained in
  this tunebook, ordered in the way they were added in this
  tunebook.