jpa-annotations

I am using the Netbeans IDE 8.0.2 and eclipselink 2.5.2. This occurring exception below when opening a connection, the problem is that this does not happen every time. The entity described in exception "Departmento" exactly follows the pattern of the other classes being that our system already contain approximately 500 entity classes and only in the new classes are taking place this exception. This entity was generated by that option "Entity Classes from Database" of Netbeans and added to the persistense XML ... Caused by: javax.persistence.PersistenceException: Exception [EclipseLink-28018]

How does @Version annotation work in JPA? I found various answers whose extract is as follows: JPA uses a version field in your entities to detect concurrent modifications to the same datastore record. When the JPA runtime detects an attempt to concurrently modify the same record, it throws an exception to the transaction attempting to commit last. But I am still not sure how it works. Also as from the following lines: You should consider version fields immutable. Changing the field value has undefined results. Does it mean that we should declare our version field as final ? But still I am not