Connect Java to relational databases using prepared statements, pooling, transactions, and isolation levels.
Database · persistence
Use the strong answer as your reference, explain it aloud in your own words, then choose how soon you want to review it again.
Interview prompt
Strong answer
JDBC gives Java explicit control over connections, statements, results, and transactions. Use prepared statements for parameters, close resources deterministically, keep transaction boundaries intentional, and understand the database isolation level rather than assuming every transaction is serializable.
Key points
Interviewer looks for
Connect Java code to database behavior: connection lifecycle, transaction ownership, isolation, locks, and failure handling.
Java example
1try (Connection connection = dataSource.getConnection();
2 PreparedStatement statement = connection.prepareStatement("select id from users where email = ?")) {
3 statement.setString(1, email);
4 try (ResultSet result = statement.executeQuery()) {
5 return result.next() ? result.getLong(1) : null;
6 }
7}Topic interview questions
These questions are tied to this lesson. Read each question aloud, then compare your explanation with the strong answer.
Strong answer
PreparedStatement binds values separately from SQL text, preventing injection and often allowing the database to reuse a query plan. It also handles type conversion more safely.
Strong answer
It should surround a coherent business use case so all required database changes commit or roll back together. Putting it around arbitrary repository calls can create partial updates or unnecessarily long locks.
Strong answer
Isolation controls which effects of concurrent transactions are visible, trading anomalies such as dirty or non-repeatable reads against concurrency and performance. The database's actual behavior depends on its engine and configuration.
Strong answer
Creating database connections is expensive and database servers have finite connection capacity. A pool reuses connections and enforces limits, but callers still need timeouts, validation, and correct close behavior.
Strong answer
Resources can remain occupied, exhausting the pool or database server and causing unrelated requests to fail. Try-with-resources should own the lifecycle of statements, result sets, and connections.
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