Interview Bite

Introduction to JDBC Interview Questions

JDBC (Java Database Connectivity) is a Java API used to connect and execute queries with databases. It is a crucial topic for Java developers, database engineers, and backend developers.

This guide covers 30+ JDBC interview questions ranging from basic concepts to advanced topics like connection pooling, transactions, and batch processing.

---

Section 1: JDBC Basics (10 Questions)

1. What is JDBC?

JDBC (Java Database Connectivity) is a Java API that enables Java applications to interact with relational databases using SQL queries.

2. What are the main components of JDBC?

• DriverManager – Manages database drivers
• Connection – Establishes a session with the database
• Statement – Executes SQL queries
• ResultSet – Stores query results

3. What are the different types of JDBC drivers?

Type	Description
Type 1	JDBC-ODBC Bridge (Deprecated)
Type 2	Native API (Part Java, Part Native)
Type 3	Network Protocol (Middleware-based)
Type 4	Pure Java (Direct-to-DB)

4. How do you load a JDBC driver?

Class.forName("com.mysql.jdbc.Driver"); // Older way (JDBC 3.0)

In JDBC 4.0+, drivers are auto-loaded via ServiceLoader.

5. How to establish a JDBC connection?

String url = "jdbc:mysql://localhost:3306/mydb";
String user = "root";
String password = "password";
Connection conn = DriverManager.getConnection(url, user, password);

6. What is the difference between Statement, PreparedStatement, and CallableStatement?

Type	Use Case
Statement	Simple SQL (no parameters)
PreparedStatement	Parameterized SQL (prevents SQL injection)
CallableStatement	Executes stored procedures

7. How to execute a SELECT query in JDBC?

Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM employees");
while (rs.next()) {
    System.out.println(rs.getString("name"));
}

8. What is a ResultSet in JDBC?

A ResultSet is a table-like object that stores the results of a SQL query.

9. How to handle transactions in JDBC?

conn.setAutoCommit(false); // Disable auto-commit
try {
    stmt.executeUpdate("INSERT INTO users VALUES (1, 'John')");
    conn.commit(); // Commit on success
} catch (SQLException e) {
    conn.rollback(); // Rollback on failure
}

10. How to close JDBC resources properly?

Use try-with-resources (Java 7+) to auto-close connections:

try (Connection conn = DriverManager.getConnection(url, user, password);
     Statement stmt = conn.createStatement()) {
    // JDBC operations
} catch (SQLException e) {
    e.printStackTrace();
}

---

Section 2: Advanced JDBC (10 Questions)

11. What is JDBC Connection Pooling?

Connection pooling reuses database connections to improve performance (e.g., HikariCP, Apache DBCP).

12. What is a DataSource in JDBC?

A DataSource is an alternative to DriverManager and supports connection pooling.

13. How to prevent SQL Injection in JDBC?

Use PreparedStatement instead of Statement:

PreparedStatement pstmt = conn.prepareStatement("SELECT * FROM users WHERE id = ?");
pstmt.setInt(1, userId);

14. What is Batch Processing in JDBC?

Batch processing groups multiple SQL queries into a single execution:

PreparedStatement pstmt = conn.prepareStatement("INSERT INTO employees VALUES (?, ?)");
pstmt.setInt(1, 101);
pstmt.setString(2, "Alice");
pstmt.addBatch(); // Add to batch
pstmt.executeBatch(); // Execute all at once

15. What are Scrollable and Updatable ResultSets?

• Scrollable ResultSet → Can move forward/backward (TYPE_SCROLL_INSENSITIVE)
• Updatable ResultSet → Can modify data (CONCUR_UPDATABLE)

16. What is JDBC RowSet?

A RowSet is a wrapper for ResultSet with additional features (disconnected mode, JavaBean support).

17. How to call a stored procedure in JDBC?

CallableStatement cstmt = conn.prepareCall("{call get_employee(?)}");
cstmt.setInt(1, empId);
ResultSet rs = cstmt.executeQuery();

18. What is Metadata in JDBC?

• DatabaseMetaData → Database info (tables, schemas)
• ResultSetMetaData → ResultSet structure (columns, types)

19. What are the common JDBC Exceptions?

• SQLException – General database error
• SQLTimeoutException – Query timeout
• BatchUpdateException – Batch execution failure

20. How to improve JDBC performance?

• Use connection pooling
• Optimize SQL queries
• Use batch processing
• Fetch only required columns

---

People Also Ask (10 Additional Questions)

JDBC Best Practices

21. Should we use Class.forName() in JDBC 4.0+?
    No, auto-loading is supported in JDBC 4.0+.
22. How to handle large data in JDBC?
    Use setFetchSize() to control row retrieval.
23. What is the difference between execute(), executeQuery(), and executeUpdate()?

• executeQuery() → SELECT
• executeUpdate() → INSERT, UPDATE, DELETE
• execute() → Any SQL

JDBC vs. Other Technologies

24. JDBC vs. Hibernate?

• JDBC → Low-level SQL control
• Hibernate → ORM (Object-Relational Mapping)

25. JDBC vs. JPA?

• JDBC → Manual SQL handling
• JPA → Higher-level abstraction (Hibernate, EclipseLink)

Troubleshooting JDBC

26. How to debug JDBC connection issues?
    Check:

• URL, username, password
• Firewall/network access
• Driver compatibility

27. What causes “No suitable driver found” error?

• Missing JDBC driver in classpath
• Incorrect JDBC URL

Advanced JDBC Features

28. Does JDBC support NoSQL databases?
    Some NoSQL databases (MongoDB, Cassandra) provide JDBC-like drivers.
29. What is XA Datasource in JDBC?
    Used in distributed transactions (JTA).
30. How to use JDBC with Spring Framework?

• JdbcTemplate (Simplifies JDBC operations)
• Spring Data JDBC (ORM alternative)

---

Conclusion

This comprehensive JDBC interview guide covers 30+ essential questions on:
✔ JDBC Basics (Connection, Statements, ResultSet)
✔ Advanced JDBC (Connection Pooling, Batch Processing)
✔ Best Practices & Troubleshooting

Next Steps:

• Practice JDBC coding examples
• Explore HikariCP for connection pooling
• Learn Spring JDBC for enterprise apps