Have you worked with transactions? What isolation levels did you use?

Yes, I have worked with transactions in Java using JDBC and Spring Transaction Management. The main isolation levels I have encountered:

• READ UNCOMMITTED — the lowest level, allows dirty reads.
• READ COMMITTED — prevents dirty reads but allows non-repeatable reads.
• REPEATABLE READ — prevents dirty and non-repeatable reads but allows phantom reads.
• SERIALIZABLE — the strictest level, provides full transaction isolation.

In most cases, I used the READ COMMITTED level for a balance between performance and consistency. In critical operations where maximum data integrity is essential, I applied SERIALIZABLE.

Example of setting the isolation level in Spring:

@Transactional(isolation = Isolation.REPEATABLE_READ)
public void updateData() {
    // business logic
}