docs: public static final synchronized void useValueFormat(String pattern)
  	{
  		if (pattern == null)
  			sdf = null;
  		else if (sdf == null) {
  			sdf = new SimpleDateFormat(pattern);
  			sdf.setCalendar(getCalendar());
  		}
  		else
  			sdf.applyPattern(pattern);
  	}