What is the purpose of the wait() method in Java?

The correct answer is A: To release the lock and make the thread wait until another thread calls notify(). wait() releases the monitor lock and causes the thread to wait until notify() or notifyAll() is called by another thread, enabling inter-thread communication.

What will happen when you compile and run this code? java List strings = Arrays.asList("a", "b", "c"); List raw = strings; raw.add(123); String s = strings.get(3);

The correct answer is C: Compiles with warning, throws ClassCastException at runtime. Assigning generic type to raw type suppresses type checking. The Integer added bypasses the type system, causing ClassCastException when retrieved as String.

Which of the following access modifiers allows a variable to be accessed only within the same class?

The correct answer is A: private. The 'private' access modifier restricts access to only within the same class. It provides the highest level of encapsulation.

Can you instantiate an interface in Java?

The correct answer is B: No, interfaces cannot be instantiated. Interfaces cannot be instantiated directly. You can only create objects of classes that implement interfaces.

Consider code that implements auto-closeable resources. What is the advantage of try-with-resources statement?

The correct answer is D: All of the above. Try-with-resources (Java 7+) automatically closes resources, handles suppressed exceptions, and closes in LIFO order without explicit close() calls.

Home

Home › Subjects › Java Programming

Java Programming

Java OOP, collections, multithreading

212 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–80 of 212

Topics in Java Programming

All Basics & Syntax 100 OOP in Java 100 Collections Framework 100 Multithreading 100 Exception Handling 100 I/O Streams 100 JDBC 100 Generics 100 Lambda Expressions 100 Spring Framework Basics 58

Q.71 Hard JDBC

A batch update operation fails partially. How can you identify which statements failed in the batch?

A Check the exception message

B Use the int array returned by executeBatch() to check individual update counts

C Re-execute the batch statement by statement

D Use savepoints for each batch statement

Correct Answer: B. Use the int array returned by executeBatch() to check individual update counts

EXPLANATION

executeBatch() returns an int array where each element represents the update count for the corresponding statement. A value of -3 (Statement.EXECUTE_FAILED) indicates failure for that statement.

Test

Q.72 Hard JDBC

Which method is used to check if a CallableStatement has a return value from a stored procedure?

A hasResult()

B wasNull()

C getReturnValue()

D getObject(int parameterIndex)

Correct Answer: B. wasNull()

EXPLANATION

The wasNull() method checks if the last value retrieved from a CallableStatement was NULL. To get the return value, you typically use getInt(), getString(), etc., and then check wasNull().

Test

Q.73 Hard JDBC

What is the default transaction isolation level in JDBC when autocommit is disabled?

A TRANSACTION_READ_UNCOMMITTED

B TRANSACTION_READ_COMMITTED

C TRANSACTION_REPEATABLE_READ

D Depends on the database driver

Correct Answer: D. Depends on the database driver

EXPLANATION

The default isolation level depends on the specific database and JDBC driver configuration. Different databases have different defaults (MySQL is REPEATABLE_READ, Oracle is READ_COMMITTED).

Test

Q.74 Hard JDBC

A developer wants to prevent SQL injection attacks while executing dynamic queries. Which approach is most secure?

A Use String concatenation with input validation

B Use PreparedStatement with setString() methods

C Use regular expressions to filter input

D Use encrypted password fields in queries

Correct Answer: B. Use PreparedStatement with setString() methods

EXPLANATION

PreparedStatement with parameterized queries is the most secure approach as it separates SQL logic from data. The database treats parameters as data, not executable code, preventing SQL injection.

Test

Q.75 Hard JDBC

What is the difference between update() and updateRow() methods in ResultSet?

A update() modifies a single column, updateRow() commits all column changes

B update() is for SELECT queries, updateRow() is for UPDATE queries

C update() is for integers, updateRow() is for all data types

D There is no difference; they are synonymous

Correct Answer: A. update() modifies a single column, updateRow() commits all column changes

EXPLANATION

update*() methods (like updateInt(), updateString()) modify individual column values in the current row, while updateRow() commits all these changes to the database.

Test

Q.76 Hard JDBC

In JDBC, what does the ResultSet.TYPE_SCROLL_INSENSITIVE constant represent?

A Non-scrollable result set

B Scrollable result set that doesn't reflect database changes

C Forward-only result set

D Bidirectional result set

Correct Answer: B. Scrollable result set that doesn't reflect database changes

EXPLANATION

TYPE_SCROLL_INSENSITIVE creates scrollable ResultSet (can move forward/backward) but changes made to database after ResultSet creation are not reflected.

Test

Q.77 Hard JDBC

Which JDBC feature allows you to call stored procedures?

A Statement

B PreparedStatement

C CallableStatement

D ExecutableStatement

Correct Answer: C. CallableStatement

EXPLANATION

CallableStatement is used to invoke stored procedures and functions. It extends PreparedStatement and supports IN, OUT, and INOUT parameters.

Test

Q.78 Hard JDBC

What is the difference between execute(), executeQuery(), and executeUpdate()?

A execute() returns boolean, executeQuery() returns ResultSet, executeUpdate() returns int

B All three are identical

C execute() is fastest, others are slower

D executeQuery() updates database, executeUpdate() retrieves data

Correct Answer: A. execute() returns boolean, executeQuery() returns ResultSet, executeUpdate() returns int

EXPLANATION

execute() returns boolean (true if ResultSet available), executeQuery() returns ResultSet for SELECT, executeUpdate() returns row count for INSERT/UPDATE/DELETE.

Test

Q.79 Hard JDBC

How would you implement batch processing in JDBC for multiple INSERT operations?

A Use addBatch() and executeBatch() methods

B Execute each insert in a loop separately

C Use multiple connections

D Create multiple statements

Correct Answer: A. Use addBatch() and executeBatch() methods

EXPLANATION

addBatch() adds SQL command to batch, executeBatch() executes all batched commands at once, improving performance significantly for multiple operations.

Test

Q.80 Hard JDBC

Consider code: String query = "SELECT * FROM users WHERE id=" + userId; stmt.executeQuery(query); What security issue exists?

A Performance degradation

B SQL Injection vulnerability

C Memory leak

D Connection timeout

Correct Answer: B. SQL Injection vulnerability

EXPLANATION

This is vulnerable to SQL injection as user input is directly concatenated. Using PreparedStatement with parameters prevents this: "SELECT * FROM users WHERE id=?"

Test

1…6 7 8 9 10…22

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming