Advanced Java Interview Questions and Answers

CHAPTER 2

JDBC Programming

2.1 The JDBC Connectivity Model

Question: What is the purpose of the setFetchSize() method in JDBC?
Answer: The setFetchSize() method specifies the number of rows to fetch from the database in a single round trip.

Question: How do you use savepoints in JDBC?
Answer: Use the setSavepoint() method to mark a point in a transaction and rollback(Savepoint savepoint) to

roll back to it.

Question: What is the purpose of DatabaseMetaData in JDBC?
Answer: DatabaseMetaData provides information about the database, such as its capabilities, tables, and drivers.

Question: What is the use of the getGeneratedKeys() method?
Answer: The getGeneratedKeys() method retrieves auto-generated keys (like primary keys) after an INSERT operation.

Question: What are row sets in JDBC?
Answer: Row sets are enhanced ResultSet objects that support features like disconnected operation and serialization.

Question: How do you perform a batch update in JDBC?
Answer: Add multiple SQL statements using addBatch() and execute them using executeBatch().

Question: What is the difference between commit() and rollback()?
Answer: commit() saves changes made in a transaction, while rollback() reverts changes.

Question: How do you check if a connection is valid in JDBC?
Answer: Use the isValid(int timeout) method of the Connection interface.

Question: What is the use of rowId in JDBC?
Answer: RowId represents a unique identifier for a row in the database and can be retrieved using getRowId().

Question: What is a Scrollable ResultSet?
Answer: A Scrollable ResultSet allows you to navigate forward and backward through the query results.

Question: How do you retrieve metadata about a ResultSet?
Answer: Use the getMetaData() method of the ResultSet object.

Question: What are the different types of statements in JDBC?
Answer: The types are Statement, PreparedStatement, and CallableStatement.

Question: How do you update data in a ResultSet?
Answer: Use ResultSet methods like updateString(), updateInt(), and updateRow() to modify data.

Question: What is connection pooling in JDBC?
Answer: Connection pooling is a technique to reuse database connections for better performance and resource management.

Question: How does JDBC support batch processing?
Answer: JDBC supports batch processing using the addBatch() and executeBatch() methods for bulk updates.

Question: How do you execute stored procedures in JDBC?
Answer: Use CallableStatement to execute stored procedures.

Question: What is the role of ParameterMetaData in JDBC?
Answer: ParameterMetaData provides information about parameters in a PreparedStatement.

Question: How can you retrieve database-specific keywords in JDBC?
Answer: Use the getSQLKeywords() method of the DatabaseMetaData object.

Question: How do you handle large binary data in JDBC?
Answer: Use Blob for binary data and Clob for large text data.

Question: What is JDBC 4.0's feature for auto-loading drivers?
Answer: In JDBC 4.0 and later, drivers are auto-loaded at runtime without explicitly calling Class.forName().

2.2 Creating a SQL Query

Question: How do you retrieve data from a SELECT query in JDBC?
Answer: Use ResultSet methods like next(), getString(), or getInt() to retrieve and process data row by row.

Question: How do you optimize performance when creating SQL queries in Java?
Answer: Use PreparedStatement for repeated queries, index database columns, and limit fetched rows.

Question: How do you handle null values in a SQL query?
Answer: Use IS NULL in the query or check for null in the application code before processing the data.

Question: What is the purpose of the setMaxRows() method in JDBC?
Answer: The setMaxRows() method limits the number of rows returned by a query.

Question: How do you use JOINs in a SQL query in JDBC?
Answer: Include JOIN clauses in the SQL query string and execute it using Statement or PreparedStatement.

Question: How do you perform a query with ORDER BY in JDBC?
Answer: Add an ORDER BY clause to the SQL query string before executing it.

Question: How do you perform a query with GROUP BY in JDBC?
Answer: Add a GROUP BY clause to the SQL query string and process the aggregated results using ResultSet.

Question: How do you perform a query with WHERE conditions in JDBC?
Answer: Add a WHERE clause to filter rows and use placeholders (?) for dynamic parameters.

Question: How do you use aggregate functions in a SQL query in JDBC?
Answer: Include aggregate functions like SUM(), COUNT(), AVG(), etc., in the query string.

Question: What is the significance of the LIMIT clause in a SQL query?
Answer: The LIMIT clause restricts the number of rows returned by a query, improving performance.

Question: How do you perform a query with a subquery in JDBC?
Answer: Include a subquery within the main SQL query string and execute it using Statement or PreparedStatement.

Question: What is the role of the LIKE operator in SQL queries?
Answer: The LIKE operator is used for pattern matching in WHERE conditions.

Question: How do you execute a query with a HAVING clause in JDBC?
Answer: Add a HAVING clause to filter aggregated results and execute the query as usual.

Question: How do you combine queries using UNION in JDBC?
Answer: Construct a query with the UNION operator and execute it using Statement or PreparedStatement.

Question: How do you handle special characters in SQL queries?
Answer: Escape special characters or use PreparedStatement to avoid issues like SQL injection.

Question: What is the purpose of the DISTINCT keyword in SQL queries?
Answer: The DISTINCT keyword removes duplicate rows from the query results.

Question: How do you update multiple rows in a SQL query?
Answer: Use an UPDATE query with a WHERE condition that matches multiple rows.

Question: How do you delete rows using a SQL query in JDBC?
Answer: Use a DELETE statement with a WHERE condition and execute it using executeUpdate().

Question: How do you insert multiple rows in a SQL query?
Answer: Use a single INSERT statement with multiple values or batch processing for better performance.

Question: How do you create a table using a SQL query in JDBC?
Answer: Use a CREATE TABLE statement and execute it using the execute() method.

2.3 Getting the Results

Question: What is the default cursor behavior of a ResultSet?
Answer: By default, a ResultSet is TYPE_FORWARD_ONLY and read-only.

Question: What is the difference between relative(int rows) and absolute(int row) in ResultSet?
Answer: relative() moves the cursor relative to its current position, while absolute() moves it to an absolute row number.

Question: How do you check the type of a ResultSet?
Answer: Use the getType() method to determine if the ResultSet is forward-only or scrollable.

Question: Can you navigate a ResultSet without rows?
Answer: No, attempting to navigate a ResultSet with no rows will cause the cursor methods to return false.

Question: How do you retrieve a timestamp from a ResultSet?
Answer: Use the getTimestamp() method to retrieve a SQL TIMESTAMP...