What are detached, persistent and transient objects in hibernate?

Question

What are detached, persistent and transient objects in hibernate? Please explain with an example.

Answer 1

A new instance of a persistent class which is not associated with a Session, has no representation in the database and no identifier value is considered transient by Hibernate:

Person person = new Person(); person.setName("Foobar"); // person is in a transient state 

A persistent instance has a representation in the database, an identifier value and is associated with a Session. You can make a transient instance persistent by associating it with a Session:

Long id = (Long) session.save(person); // person is now in a persistent state 

Now, if we close the Hibernate Session, the persistent instance will become a detached instance: it isn't attached to a Session anymore (but can still be modified and reattached to a new Session later though).

All this is clearly explained in the whole Chapter 10. Working with objects of the Hibernate documentation that I'm only paraphrasing above. Definitely, a must-read.