Interview Point of view Mostly Asked Questions in Hibernate:
In Interview point view most important questions are given bellow.These are all questions in Hibernate. In real time hibernate place a very important role in applications.By using Hibernate we can connect the application with database better than the jdbc and more features are available in hibernate.
1.what is the nee d of the Dialect in Configuration file of the Hibernate?
ans: To generate the database related sql queries internally Dialect is used.
2.what is the benefit of Configuration file name as hibernate.cfg.xml?
ans:--> if the file name is hibernate.cfg.xml then it is optional to pass the file name as parameter to Configure().
-->if the file name is some other say krishna.cfg.xml the we need to pass the configuration file name to Configure() as mandatory.
for example:
i) if the file name is hibernate.cfg.xml
conf.configure( ); ----->correct
conf.configure("hibernate.cfg.xml");---->correct
ii)if the file name is krishna.cfg.xml then
conf.configure( ); ----->wrong
conf.configure("krishna.cfg.xml");----->correct
3.what is the difference between load( ) method and get( ) method?
ans: load( ) method
--> if the given id is doesn't exits in the database then load( ) method throws
Object NotFoundException.
--->load( ) method reads an object from the database when is accessed in the code ,but not immediately load( ) method called.This is called
"lazy loading"
get( )method
---> if the given id is doesn't exists in the hibernate then get( )method simply returns
null.
--->get( ) method reads an object from the database when accessed in the code,immediately get( ) method called .This is called
"early loading".
4.In hibernate application how many states are contain a pojo class object?
ans: In hibernate application a pojo class can contain 3 states.They are
1.Transient State
2.Persist State
3.Detached State
Transient State:
--->if the object is not entered into the session then the object is in Transient State.So it is not associated with database.
---->if any changes are done on a Transient state object it is not effected on the database.
Persistent State:
---> if the object is entered into the session then the object is in Persistent State.So it is associated with database.
---->if any changes are done on a Persist state object is effected on the database.
Detached State:
---->if the object is come out of the session then the object is in Detached State.So it is not associated with database.
---->if any changes are done on the database object is not effected on the database.
5.what is the difference between update() method and merge( )method?
ans:-->update( )method and merge( )method both are used to convert the object from detached state to persist state
update( ) method:
-->we can call the update( ) method to convert a detached state object into persist state.while converting if already an object exits in a cash with the same id then update( ) method throws
org.hibernate.NonUniqueObjectException it means update( ) method fails.
merge( )method:
---->we can call the merge( )method to convert a detached state object to persist state.while converting if already an object with same id exists in the cash then merge( ) just copies the changes from detached state to object which is already exists in the cash.But it
does not throw any Exception.
