A Mock Aboute EntityManager

[Fu Dong Jia]

Given:
11. @PersistenceContext EntityManager em;
12. public boolean test(Order o) {
13. boolean b = false;
14. o = em.merge(o);
15 em.remove(o);
16. o = em.merge(o);
17. b = em.contains(o);
18. return b;
19. }
Pass4Side SUN 310-091
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Which statement is correct?
A. The method will return TRUE.
B. The method will return FALSE.
C. The method will throw an exception.
D. The Order instance will be removed from the database.
Answer: C

Why the answer is c?

[Chaminda Amarasinghe]

javadocs of EM for merge


/**
* Merge the state of the given entity into the
* current persistence context.
* @param entity
* @return the instance that the state was merged to
* @throws IllegalArgumentException if instance is not an
* entity or is a removed entity
* @throws TransactionRequiredException if invoked on a
* container-managed entity manager of type
* PersistenceContextType.TRANSACTION and there is
* no transaction.
*/
public <T> T merge(T entity);