一个日期类 Date，其功能包括： （1）能够以不同的格式输出日期，如： MM/DD/YYYY (String, String, String) June 14, 2014 (String, int, int) 2015 年 3 月6 日 (int, int, int) （2）定义三个重载的构造函数，在创建 Date 对象时，可用以上三种格式来进行初始化。

-A date class Date, which include: (1) can be in different formats to output the date, such as: MM/DD/YYYY (String, String, String) June 14, 2014 (String, int, int) 2015 on March 6, constructor day (int, int, int) (2) defines three overloaded, when you create a date object that can be used to initialize the above three formats.