Is it using some kind of byte codes modification to the original classes?

Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version?

I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem.

If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough.

So, the questions are:

1. How does Hibernate know if a property of an object is changed?

2. Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references?

   And, also,

3. Would hashCode()/equals() with only the id field be enough?