A Java date‑formatting bug occurs when the week‑based year pattern 'YYYY' is used instead of the calendar year 'yyyy', causing dates near year‑end to display the next year, and this article explains the cause, demonstrates it with code, and shows how to avoid it.
The article explains a subtle Java date‑formatting bug where using the week‑based year pattern (YYYY) can incorrectly display the next calendar year for dates at year‑end, demonstrates the issue with sample code, and clarifies why yyyy should be used for ordinary year representation.
This article explains why using uppercase YYYY or DD in Java date‑format patterns can produce incorrect results around year boundaries, demonstrates the bugs with concrete code examples, and clarifies the correct usage of lowercase yyyy and dd for calendar dates.
A Java developer discovers that formatting dates with the pattern “YYYY‑MM‑dd” causes a year‑off bug on New Year's Day, learns that “YYYY” denotes a week‑based year, and is advised to always use “yyyy‑MM‑dd” for reliable calendar dates.
Around the 2020 New Year many Java applications displayed dates like 2020/12/31 due to a subtle bug in SimpleDateFormat when using the pattern "YYYY" instead of "yyyy", which can be reproduced, explained, and resolved with a simple pattern change.
