用整数存储私有成员：年、月和日。为类提供构造函数，能够对各成员进行初始

化，但出现错误的初值时, 成员为2000-1-。也可以不在不提供任何初值的情况

下日期为2000-1-1。另外可以用一个Date 对象进行初始化，成员函数应实现以

下功能：

（1） 对所有成员一次性赋值，也能对某个成员单独赋值，能够一次返回所有成

员的值，也能单独返回某个成员的值

（2） 可以按照mm-dd-yyyy 格式输出日期。

（3） 有成员函数nextDay（），用于将日期增加一天-Integer stored the private Members: year, month, and day. Class provides a constructor to initialize the members, but the wrong initial value, members 2000-1-. The date can also be not the case does not provide any initial value 2000-1-1. Also available on a Date object is initialized, the member function should achieve the following functions: (1) all members of the one-time assignment, can also be a member of a separate assignment, to return once the value of all the members, but also separate return a The members of the value (2) according to the date of mm-dd-yyyy format output. (3) member function nextDay () for additional day date