public int compareTo(Object date) {
		if (date == null) {
			throw new NullPointerException("用于比较的指定日期对象不能为null。");
		} else if (this == date) {
			return 0;
		}
		long diff = calendar.getTimeInMillis() - getTimeOfDate(date);
		if (diff == 0)
			return 0;
		return diff > 0 ? 1 : -1;
	}