code: public synchronized Set<String> keySet() {
  		if(size == 0) {
  			return new HashSet<String>(0);
  		} else {
  			try {
  				XAttributeMap map = deserialize();
  				return map.keySet();
  			} catch (IOException e) {
  				e.printStackTrace();
  				return null;
  			}
  		}
  	}
docs: /* (non-Javadoc)
  @see java.util.Map#keySet()