说明：  编写一个Java应用程序，当用户在输入对话框中输入两个日期后（日期格式为YYYYMMDD，如1999年1月12日应输入为19990112），程序将判断两个日期的先后顺序，以及两个日期之间的间隔天数（例如1999年1月1日和1999年1月2日之间的间隔是1天）
(Write a Java application, when a user in the input dialog box, enter the two after the date (the date format YYYYMMDD, such as the January 12, 1999 should be entered as 19,990,112), the program will determine the order in two dates, as well as two the interval between the date of the number of days (for example, January 1, 1999 and January 2, 1999 is the interval between 1 day))