编写一个Application程序MyDate.java，建立日期类，接受用户输入的年、月、日，完成日期增加若干天得到新的日期，日期推前若干天得到新的日期，日期与日期间相差多少天的计算。(Write a Application program MyDate.java, establish the date class, accept the user input year, month, day, completion date increase several days to get the new date, the date before the date to get a new date, the date and date difference between the number of days calculation.)