JDBC Interview Questions and Answers for internship

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JDBC Internship 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 standard way to execute SQL statements, query data, and update databases.

  2. What are the core interfaces of JDBC?

    • Answer: The core interfaces include `Connection`, `Statement`, `PreparedStatement`, `CallableStatement`, `ResultSet`, and `DriverManager`.

  3. Explain the role of the `DriverManager` class.

    • Answer: `DriverManager` manages a list of registered JDBC drivers. It's used to establish a connection to a database using the `getConnection()` method, which takes a JDBC URL, username, and password as arguments.

  4. What is a JDBC driver? Name some common types.

    • Answer: A JDBC driver is a software component that allows Java applications to connect to and interact with a specific database system. Common types include Type 1 (JDBC-ODBC Bridge), Type 2 (Native-API), Type 3 (Network Protocol), and Type 4 (Thin Driver).

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

    • Answer: `Statement` executes simple SQL queries. `PreparedStatement` is used for parameterized queries, improving performance and security by preventing SQL injection. `CallableStatement` executes stored procedures.

  6. Explain the use of `ResultSet`.

    • Answer: `ResultSet` holds the data retrieved from a database query. It provides methods to navigate through the result set (e.g., `next()`, `getInt()`, `getString()`), accessing the data row by row.

  7. How do you handle database exceptions in JDBC?

    • Answer: Use `try-catch` blocks to handle `SQLExceptions`. Always close database resources (connections, statements, result sets) in a `finally` block to prevent resource leaks.

  8. What is a connection pool and why is it used?

    • Answer: A connection pool is a technique that pre-creates a set of database connections, which are reused by applications to reduce the overhead of establishing new connections each time.

  9. How do you prevent SQL injection?

    • Answer: Use parameterized queries (`PreparedStatement`) instead of directly concatenating user input into SQL strings. This prevents malicious code from being executed.

  10. What is the JDBC URL format? Give an example.

    • Answer: The general format is `jdbc::`. An example for MySQL is: `jdbc:mysql://localhost:3306/mydatabase`.

  11. Explain the different transaction isolation levels in JDBC.

    • Answer: JDBC supports various isolation levels (e.g., `TRANSACTION_READ_UNCOMMITTED`, `TRANSACTION_READ_COMMITTED`, `TRANSACTION_REPEATABLE_READ`, `TRANSACTION_SERIALIZABLE`) that control how transactions interact and see changes made by other transactions.

  12. How do you perform batch updates in JDBC?

    • Answer: Use the `addBatch()` method of `Statement` or `PreparedStatement` to add multiple SQL statements to a batch. Then, execute the batch using `executeBatch()`.

  13. What are stored procedures and how do you call them using JDBC?

    • Answer: Stored procedures are pre-compiled SQL code stored in the database. You call them using `CallableStatement`.

  14. How do you handle large result sets efficiently in JDBC?

    • Answer: Use techniques like fetching data in batches (`setFetchSize()`) or using cursors to process large result sets incrementally instead of loading everything into memory at once.

  15. What is the difference between `executeUpdate()` and `executeQuery()`?

    • Answer: `executeUpdate()` is used for SQL statements that modify data (INSERT, UPDATE, DELETE). `executeQuery()` is used for SQL statements that retrieve data (SELECT).

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