public long between(DateUnit unit) {
		long diff = end.getTime() - begin.getTime();
		return diff / unit.getMillis();
	}
public long between ( DateUnit unit ) { long diff = end . getTime ( ) - begin . getTime ( ) ; return diff / unit . getMillis ( ) ; }
判断两个日期相差的时长<br>
返回 给定单位的时长差

@param unit 相差的单位：相差 天{@link DateUnit#DAY}、小时{@link DateUnit#HOUR} 等
@return 时长差