计算二日期的间隔天数，计算某日期为星期几，打印对象当前数据的y年m月的月历，一次增加若干天，对两个日期进行其他比较运算等。-Second, the interval between the date of calculation of the number of days to calculate a date for the week, print the current data object y years m months of the calendar, the first incre