Java Programming — JDBC Questions & Answers

Q.11 Medium JDBC

In JDBC 2024-25, which data type mapping is incorrect for Java to SQL?

A int → INTEGER

B String → VARCHAR

C boolean → BOOLEAN

D byte[] → CHAR

Correct Answer: D. byte[] → CHAR

EXPLANATION

byte[] should map to BLOB (Binary Large Object), not CHAR. CHAR is for single character types.

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Q.12 Easy JDBC

What is the difference between commit() and rollback() in JDBC transactions?

A commit() saves changes, rollback() undoes them

B Both perform the same function

C rollback() is faster than commit()

D commit() is used for SELECT queries, rollback() for UPDATE

Correct Answer: A. commit() saves changes, rollback() undoes them

EXPLANATION

commit() permanently saves all changes made during the transaction, while rollback() discards all changes and reverts to the previous state.

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Q.13 Hard JDBC

A developer wants to retrieve data from a stored procedure that returns multiple result sets and output parameters. Which approach is correct?

A Use Statement with executeQuery()

B Use PreparedStatement with execute()

C Use CallableStatement with registerOutParameter() and execute()

D Use PreparedStatement with setFetchSize()

Correct Answer: C. Use CallableStatement with registerOutParameter() and execute()

EXPLANATION

CallableStatement is specifically designed for stored procedures, supporting registerOutParameter() for output parameters and getMoreResults() for multiple result sets.

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Q.14 Medium JDBC

Which method in ResultSet is used to check if a column value is NULL?

A isNull()

B wasNull()

C checkNull()

D getNullValue()

Correct Answer: B. wasNull()

EXPLANATION

wasNull() returns true if the last retrieved value was NULL in the database, checked after calling a getter method like getString() or getInt().

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Q.15 Medium JDBC

In a multi-threaded JDBC application, what should be the approach for Connection object usage?

A Share single Connection object across all threads

B Each thread should use its own Connection from the pool

C Create new Connection for each database operation

D Use static Connection objects

Correct Answer: B. Each thread should use its own Connection from the pool

EXPLANATION

Connection objects are not thread-safe. Each thread should obtain its own Connection from a thread-safe connection pool to avoid race conditions.

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Q.16 Medium JDBC

What does the setMaxRows() method in Statement do?

A Limits the number of rows returned by a query

B Sets the maximum number of connections

C Defines batch size for updates

D Controls transaction timeout

Correct Answer: A. Limits the number of rows returned by a query

EXPLANATION

setMaxRows() limits the number of rows returned by executeQuery(), useful for memory management when dealing with large result sets.

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Q.17 Easy JDBC

Which exception is thrown when a JDBC driver is not found in the classpath?

A SQLException

B ClassNotFoundException

C DriverNotFoundException

D JDBCException

Correct Answer: B. ClassNotFoundException

EXPLANATION

When Class.forName() cannot locate the driver class, it throws ClassNotFoundException, indicating the driver JAR is not in the classpath.

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Q.18 Medium JDBC

Consider a scenario where a developer uses getConnection() without closing it. What is the potential impact?

A Database performance remains unaffected

B Connection leak occurs, exhausting available database connections

C Automatic rollback happens

D Query execution becomes slower temporarily

Correct Answer: B. Connection leak occurs, exhausting available database connections

EXPLANATION

Unclosed connections remain allocated and unavailable for other operations, eventually exhausting the connection pool and causing connection exhaustion errors.

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Q.19 Medium JDBC

What is the purpose of Connection pooling in JDBC applications?

A To store query results temporarily

B To reuse database connections instead of creating new ones each time

C To encrypt database connections

D To monitor database performance

Correct Answer: B. To reuse database connections instead of creating new ones each time

EXPLANATION

Connection pooling maintains a pool of reusable connections, reducing the overhead of creating new connections for each request, improving application performance.

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Q.20 Medium JDBC

A developer needs to execute a query that returns multiple result sets. Which Statement type should be used?

A Statement with executeQuery()

B PreparedStatement with setFetchSize()

C Statement with execute() or PreparedStatement with execute()

D CallableStatement only

Correct Answer: C. Statement with execute() or PreparedStatement with execute()

EXPLANATION

The execute() method returns a boolean and can handle multiple result sets via getResultSet(), getUpdateCount(), and getMoreResults() methods.

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