Will the database automatically change if object fields are modified within a transaction without explicit save?

In Java, if you use ORM (such as Hibernate) and work with objects within a transaction, changes to the object's fields can be automatically committed to the database upon transaction commit, even without explicitly calling a save method.

This is due to the change tracking mechanism (dirty checking) that ORM performs for managed entities.

However, if the object is not managed (detached or transient), or if you do not use ORM with such a mechanism, changes will not be automatically saved.

Example with Hibernate:

session.beginTransaction();
User user = session.get(User.class, userId);
user.setName("New Name"); // change field
session.getTransaction().commit(); // changes will be saved automatically

Thus, automatic database modification depends on the context and the technologies used.