“YYYY format” 是 “ISO week numbering system”
“yyyy format” 是 “Gregorian Calendar”
There are two things to note about this example:
yyyyto specify the year component. A common mistake is to use
yyyyspecifies the calendar year whereas
YYYYspecifies the year (of “Week of Year”), used in the ISO year-week calendar. In most cases,
YYYYyield the same number, however they may be different. Typically you should use the calendar year.
13:00. In iOS, however, if the user has switched 24-Hour Time to Off, the time may be