I have read the article from wiki and ,
the this way of implementing equals and hashcode() is
really weird.
Can't hibernate enhance equals/hashcode() too?
say , when add 2 new instance in session,
hibernate compare them with instance equality,
when 2 detached compared,or 1 detached instance with
1 instance loaded in session,
hibernate can compare them with orig ID(
hibernate may enhance out a new field ,say ,$origID,
and when instance detached, save origID in it).

Is that too hard or do i miss something?

Hibernate has nothing to do with equals() and hashCode().

Also, you *do* miss something, namely: it doesn't work to change the rules you use for equals(). Because the contract is that two things that are equals() must also have the same hashCode(). So if you change the behavior of equals(), you must also change the behavior of hashCode().

But if you are changing your equals() rules based on BOTH objects that you are comparing, then there is no way to know what your rules for hashCode() should be!

Basically, you can't do the kind of situational comparison you want, since most of the time you aren't actually comparing anything -- you're just generating a hashcode based on one individual object.

Cheers,
Rob

oh,I get it.
Then i'm thinking another way of solving this problem,
to those entities who need be used in set, can use dual id
to solve this problem.
private long dualID;
// generate at new() using uuid.hex, and save it in database.
then use this dualID for identity comparing in Set.