1. when I associate user with bank and the case where user have many bank object so when I try to insert bank should we need to load the user object inside of bank or is not required?
ANS-:
You should initialise user and then add bank object to it. If bank can not be without user put not null constraint on the user in bank object.
in add bank method of user use bank.setUser(this) to maintain relation.
2. about point one in the case of many to many relation ship how to handle?
I am not able to get the scenario can you please specify more? but if your question is about how to map then you will require a mapping table in middles something like user_bank_group where one column is user id and other is bank.
3. what is the advantage of implement association in hibernate instead of develop project without hibernate association?
Well there are many ORM advantages while writing queries, managing data and association.
Few are it will be lot quicker to develop as you can concentrate on business logic rather than stuff like writing logic to retrieve and convent to objects, you can manage whether every time user object is created whether to fetch all banks with it always or bring from db only when needed.
Hope this helps