I used to be pulled into various issue troubleshooting. Several occurrences are related to SimpleDateFormat & java.util.Date from various different developers and teams.
It’s not rocket science for most of experienced developers. But for some new programmer, it is one of the most messed up places.
Now Java 8 is moving these to immutable. Java 8 java.time core date related classes are immutable:
(I guess Scala’s popularity nowadays should not be a surprise.)