code: public int getHighestReferenceNumber() {
  		int max = -1;
          for (Object o : m_tunes.keySet()) {
              Integer i = (Integer) o;
              if (i > max)
                  max = i;
          }
  		return max;
  	}
docs: Returns the highest reference number from all the reference numbers this
  tunebook contains.
  
  @return The highest reference number from all the reference numbers this
  tunebook contains. -1 is returned if no tune is stored in this
  tunebook