datetimeformatter: DateTimeFormatter cheat sheet module (pattern letters incl. the four hour letters, yyyy vs YYYY week-year bug and WeekFields, en_IN locales and the U+202F AM/PM trap with parseLenient fix, SMART/STRICT/LENIENT parsing, ISO constants, SimpleDateFormat thread safety), 18 contract tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_017ic4b3fvyFpxThdRxcozLx
2026-11-14 01:24:52 +05:30
parent c8588ae520
commit 5faa57bb2d
22 changed files with 944 additions and 0 deletions
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+== 31 February under three resolver styles (pattern dd-MM-uuuu) ==
+STRICT   DateTimeParseException: Text '31-02-2026' could not be parsed: Invalid date 'FEBRUARY 31'
+SMART    2026-02-28
+LENIENT  2026-03-03
+
+== 30 February and 32 January ==
+SMART 30-02-2026 2026-02-28
+SMART 32-01-2026 DateTimeParseException: Text '32-01-2026' could not be parsed: Invalid value for DayOfMonth (valid values 1 - 28/31): 32
+
+== STRICT with yyyy: year-of-era needs an era, so it cannot resolve ==
+yyyy  DateTimeParseException: Text '14-11-2026' could not be parsed: Unable to obtain LocalDate from TemporalAccessor: {MonthOfYear=11, DayOfMonth=14, YearOfEra=2026},ISO of type java.time.format.Parsed
+uuuu  2026-11-14
+
+== how many digits? MM wants two, M accepts one or two ==
+yyyy-MM-dd  2026-1-5   DateTimeParseException: Text '2026-1-5' could not be parsed at index 5
+yyyy-M-d    2026-1-5   2026-01-05
+yyyy-M-d    2026-01-05 2026-01-05
+
+== two-digit years are read as 2000-2099 ==
+01-01-30 -> 2030-01-01
+01-01-99 -> 2099-01-01
+
+== month names are case-sensitive unless you say otherwise ==
+14 Nov 2026 2026-11-14
+14 NOV 2026 DateTimeParseException: Text '14 NOV 2026' could not be parsed at index 3
+14 NOV 2026 (parseCaseInsensitive) 2026-11-14
+
+== the old SimpleDateFormat, same 31-02-2026 ==
+lenient (default): Tue Mar 03 00:00:00 IST 2026
+setLenient(false): ParseException: Unparseable date: "31-02-2026"