KITFORMA · EDITORIAL ANSWER
Why does a Java date formatter print next year for a late-December date?
KitForma editorial guide. Calendar years and week-based years diverge near some year boundaries. A pattern copied from another library may select the wrong concept.
Step-by-step answer
Calendar years and week-based years diverge near some year boundaries. A pattern copied from another library may select the wrong concept.
For an ordinary ISO-like calendar date, use an appropriate formatter such as DateTimeFormatter.ISO_LOCAL_DATE, or a documented
uuuu-MM-dd pattern when custom composition is needed. Reserve week-based year fields for a complete week-date format with matching week and weekday semantics. Avoid a visual replacement of every capital letter in a format string.
Verify dates at both ends of the year under the intended locale and compare parsed values, not just printed labels. Year-of-era and proleptic year are also distinct; historical or era-based dates need their own contract.Sources and verification
Sources checked:
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