Explain what atomicity means in the ACID model and why it is important for transaction processing.

Atomicity in the ACID model means that a transaction is considered an indivisible unit of work: either all operations within the transaction are successfully completed, or none are applied (rollback). This is important to ensure data integrity in case of failures, errors, or concurrent access.

For example, when transferring money from one account to another, the transaction should:

1. Debit the amount from the first account.
2. Credit the amount to the second account.

If an error occurs after the debit but before the credit, atomicity guarantees that the debit will be rolled back, and the money will not be lost.

In Java, transactions are often managed using APIs, such as javax.transaction.UserTransaction or Spring Transaction Management, where you can explicitly start, commit, or rollback a transaction.