CodeQL documentation

Suspicious date format

ID: java/suspicious-date-format
Kind: problem
Severity: warning
Precision: high
   - correctness
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

The Java SimpleDateFormat class provides many placeholders so that you can define precisely the date format required. However, this also makes it easy to define a pattern that doesn’t behave exactly as you intended. The most common mistake is to use the Y placeholder (which represents the ISO 8601 week year), rather than y (which represents the actual year). In this case, the date reported will appear correct until the end of the year, when the “week year” may differ from the actual year.


Ensure the format pattern’s use of Y is correct, and if not replace it with y.


The following example uses the date format YYYY-MM-dd. On the 30th of December 2019, this code will output “2020-12-30”, rather than the intended “2019-12-30”.

System.out.println(new SimpleDateFormat("YYYY-MM-dd").format(new Date()));

The correct pattern in this case would be yyyy-MM-dd instead of YYYY-MM-dd.