JDBC Interview Questions and Answers for experienced

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100 JDBC Interview Questions and Answers

  1. What is JDBC?

    • Answer: JDBC (Java Database Connectivity) is an API that allows Java programs to interact with relational databases. It provides a set of classes and interfaces for establishing connections, executing queries, and processing results.

  2. Explain the different JDBC drivers.

    • Answer: There are four types of JDBC drivers: Type 1 (JDBC-ODBC Bridge), Type 2 (Native-API/partly Java), Type 3 (Net-protocol/all Java), and Type 4 (Native-protocol/all Java). Type 4 is generally preferred for its performance and portability.

  3. What are the steps involved in connecting to a database using JDBC?

    • Answer: 1. Load the JDBC driver. 2. Establish a connection using DriverManager.getConnection(). 3. Create a Statement, PreparedStatement, or CallableStatement object. 4. Execute SQL queries or stored procedures. 5. Process the results. 6. Close the connection.

  4. What is a PreparedStatement and why is it preferred over Statement?

    • Answer: PreparedStatement is a pre-compiled SQL statement. It improves performance by preventing SQL injection vulnerabilities and reusing the compiled statement for multiple executions with different parameters.

  5. Explain the concept of transactions in JDBC.

    • Answer: Transactions ensure atomicity, consistency, isolation, and durability (ACID) properties in database operations. JDBC provides methods like `setAutoCommit(false)` to begin a transaction, `commit()` to save changes, and `rollback()` to undo changes in case of errors.

  6. How do you handle exceptions in JDBC?

    • Answer: Use try-catch blocks to handle SQLExceptions and other exceptions that may occur during database operations. Always close resources (connections, statements, result sets) in finally blocks to prevent resource leaks.

  7. What is ResultSet and its different types?

    • Answer: ResultSet is a table of data retrieved from a database query. Types include TYPE_FORWARD_ONLY (default), TYPE_SCROLL_INSENSITIVE, and TYPE_SCROLL_SENSITIVE, determining the navigation capabilities.

  8. Explain the difference between `Statement`, `PreparedStatement`, and `CallableStatement`.

    • Answer: `Statement` executes simple SQL queries. `PreparedStatement` executes pre-compiled queries with parameters, preventing SQL injection. `CallableStatement` executes stored procedures.

  9. How do you handle database connection pooling in JDBC?

    • Answer: Connection pooling improves performance by reusing database connections instead of creating new ones for each request. Use connection pooling libraries like Apache Commons DBCP or HikariCP.

  10. What is the role of `DriverManager` in JDBC?

    • Answer: `DriverManager` manages a list of JDBC drivers and provides methods to establish database connections based on connection URLs.

  11. How do you handle BLOBs and CLOBs in JDBC?

    • Answer: BLOBs (Binary Large Objects) and CLOBs (Character Large Objects) are handled using `getBytes()` and `getCharacterStream()` methods of `ResultSet` for retrieval and `setBytes()` and `setCharacterStream()` for updates.

  12. Explain the concept of stored procedures and how to call them using JDBC.

    • Answer: Stored procedures are pre-compiled SQL code stored in the database. They are called using `CallableStatement` in JDBC, specifying the procedure name and parameters.

  13. How do you deal with concurrency issues in JDBC?

    • Answer: Use appropriate isolation levels in transactions to control how concurrent transactions interact with each other, preventing issues like dirty reads, phantom reads, etc. Utilize optimistic or pessimistic locking mechanisms as needed.

  14. What are the advantages of using JDBC?

    • Answer: Platform independence, database independence (with appropriate drivers), strong typing, and robust error handling are key advantages.

  15. What are some common JDBC performance issues and how to resolve them?

    • Answer: Inefficient queries, lack of connection pooling, improper use of transactions, and insufficient resource management are common issues. Solutions include optimizing SQL, using connection pooling, tuning transaction settings, and carefully managing resources.

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