Java 8 DateFormatter week of month and year key symbols difference

Question

I am new to java.time. Please, be patient. What is the difference between

  Symbol  Meaning                     Presentation      Examples
  ------  -------                     ------------      -------
    F       week-of-month               number            3
    W       week-of-month               number            4

isn't it just

  Symbol  Meaning                     Presentation      Examples
  ------  -------                     ------------      -------
    F/W       week-of-month               number            3

and

  Symbol  Meaning                     Presentation      Examples
  ------  -------                     ------------      -------
   Y       week-based-year             year              1996; 96
   u       year                        year              2004; 04
   y       year-of-era                 year              2004; 04

https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html

You ~never want to use `Y` instead of `y`, or you'll probably suffer the same outage that took down Twitter: http://www.juandebravo.com/2015/04/10/java-yyyy-date-format/ — Louis Wasserman, Nov 02 '16 at 21:35

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

2

The difference between u and y has already been addressed: What is the difference between year and year-of-era?

Difference between `W` and `F`

There is a bug in the javadoc for F.

W is the week of month, as represented by Weekfields::weekOfMonth:

This represents the concept of the count of weeks within the month where weeks start on a fixed day-of-week, such as Monday.

F is the aligned day of week in month, as represented by ChronoField.ALIGNED_DAY_OF_WEEK_IN_MONTH:

This represents the concept of the count of days within the period of a week where the weeks are aligned to the start of the month.

F behaves similarly in DateTimeFormatter and SimpleDateFormat.

Example: if you use 2016-11-07 as an input, W will return 2 (2nd week of the month) but F will return 7 (7th day of the first aligned week, which starts on the 1st of the month).

edited Jun 20 '20 at 09:12

Community

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answered Nov 04 '16 at 12:45

assylias

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so, `2016-11-08` yields 1 for `F`? is there also smth like `aligned_week_number`? – Antonio Nov 06 '16 at 16:06
Yes. I don't think so. – assylias Nov 06 '16 at 22:04
There is no letter for ChronoField.ALIGNED_WEEK_OF_MONTH or ALIGNED_WEEK_OF_YEAR, but the value can be output via `DateTimeFormatterBuilder` – JodaStephen Nov 07 '16 at 17:04
If it doesn't turn up in the public system in the next month, ping me – JodaStephen Nov 08 '16 at 10:35

Java 8 DateFormatter week of month and year key symbols difference

1 Answers1

Difference between W and F

Difference between `W` and `F`