Sun warns you about this in a rather odd statement in the Java API.
"[I]t is recommended that code not view
Timestampvalues generically as an instance of
java.util.Date. The inheritance relationship between
java.util.Datereally denotes implementation inheritance, and not type inheritance."
does not mean
So, what? Gavin King says:
"Note that no self-respecting code should EVER call equals on a Timestamp."
But when you start putting objects into java.util.Collections, you no longer directly control if or when an equals method is called on your objects.
This lead me to post a bug report (and proposed fix) since what I saw in our project was that upon each transaction, either our POJO had all its Dates or non at all, alternating with each call. Clearly not good! The call was supposed to be idempotent.
Sadly, there has been no interest in my bug report. And although my fix works (albeit somewhat inefficiently), it would be nice to see Hibernate keep java.util.Dates as java.util.Dates.