1. The Javajava.util.Dateandjava.util.CalendarClasses are not easy to use, do not support time zones, and they are not thread-safe;
  2. A class for formatting datesDateFormatIs placed onjava.textPackage, it is an abstract class, so we need to instantiate oneSimpleDateFormatObject to handle date formatting, andDateFormatIt’s also not thread-safe, which means if you’re calling the same thing in a multithreaded programDateFormatObject, will get unexpected results.
  3. The calculation of dates is tedious and error prone, because the months start at zero, fromCalendarYou need to add one to indicate the current month.