What does Collections.unmodifiableList() return?

The correct answer is A: A list that cannot be modified. Collections.unmodifiableList() returns a read-only view of the list. Any modification attempts throw UnsupportedOperationException.

Consider this generic interface: interface Comparable { int compareTo(T o); } Which class definition correctly implements this?

The correct answer is A: class MyClass implements Comparable { public int compareTo(MyClass o) { return 0; } }. Option A correctly implements the generic interface by specifying the concrete type parameter as MyClass in the implements clause.

What is the difference between Consumer and Function functional interfaces?

The correct answer is B: Function returns a value, Consumer doesn't. Function takes parameter T and returns R. Consumer takes parameter T and returns void.

What does the volatile keyword guarantee in multithreading?

The correct answer is B: Visibility of changes across threads and prevents instruction reordering. volatile ensures that changes to a variable are immediately visible to all threads and prevents the JVM from reordering instructions. However, it doesn't make operations atomic.

What will be the output of the following code snippet? java class Test extends Thread { public void run() { System.out.print("T"); } } public class Main { public static void main(String[] args) { Test t = new Test(); t.run(); t.start(); } }

The correct answer is A: TT. First t.run() executes directly (prints T), then t.start() creates a new thread and calls run() again (prints T). So output is TT.

Home

Home › Subjects › Java Programming

Java Programming

Java OOP, collections, multithreading

270 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–80 of 270

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 Easy Generics

Which keyword is used to declare a generic class in Java?

B generic

C template

D type

Correct Answer: A.

EXPLANATION

<T> is the standard syntax for declaring a generic type parameter in Java classes.

Test

Q.72 Easy Generics

What is the primary purpose of Generics in Java?

A To provide type safety and eliminate type casting

B To increase memory allocation

C To reduce code compilation time

D To automatically manage garbage collection

Correct Answer: A. To provide type safety and eliminate type casting

EXPLANATION

Generics enable type safety at compile time and eliminate the need for explicit type casting, reducing runtime errors.

Test

Q.73 Easy JDBC

In a JDBC application, which interface is responsible for executing SQL queries and returning ResultSet objects?

A Statement

B Connection

C Driver

D DataSource

Correct Answer: A. Statement

EXPLANATION

The Statement interface is used to execute SQL queries. Connection creates the statement, Driver manages connections, and DataSource provides connection pooling, but Statement is the actual executor.

Test

Q.74 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.

Test

Q.75 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.

Test

Q.76 Easy JDBC

In JDBC, what does the BatchUpdate feature allow developers to do?

A Execute single queries faster

B Execute multiple queries in a single batch for improved performance

C Create backup of database

D Monitor database connections

Correct Answer: B. Execute multiple queries in a single batch for improved performance

EXPLANATION

addBatch() and executeBatch() methods allow multiple SQL statements to be grouped and executed together, reducing network traffic and improving performance.

Test

Q.77 Easy JDBC

Which method of Connection interface is used to start a transaction in JDBC?

A setAutoCommit(false)

B beginTransaction()

C startTransaction()

D createTransaction()

Correct Answer: A. setAutoCommit(false)

EXPLANATION

setAutoCommit(false) disables auto-commit mode, allowing manual control over transactions through commit() and rollback() methods.

Test

Q.78 Easy JDBC

What is the correct sequence to establish a JDBC connection in Java?

A Load Driver → Create Connection → Execute Query → Close Connection

B Create Connection → Load Driver → Execute Query → Close Connection

C Load Driver → Create Statement → Execute Query → Close Connection

D Create Statement → Load Driver → Create Connection → Execute Query

Correct Answer: A. Load Driver → Create Connection → Execute Query → Close Connection

EXPLANATION

The correct JDBC connection sequence is: Class.forName() → DriverManager.getConnection() → Create Statement → Execute Query → Close resources.

Test

Q.79 Easy JDBC

Which interface in JDBC is used to execute parameterized queries and prevent SQL injection attacks?

A Statement

B PreparedStatement

C CallableStatement

D Connection

Correct Answer: B. PreparedStatement

EXPLANATION

PreparedStatement is used for parameterized queries with placeholders (?), which prevents SQL injection by separating SQL logic from data.

Test

Q.80 Easy JDBC

In JDBC, what does the executeQuery() method return?

A int

B boolean

C ResultSet

D void

Correct Answer: C. ResultSet

EXPLANATION

executeQuery() returns a ResultSet containing the rows fetched from the database for SELECT queries.

Test

1…6 7 8 9 10…27

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming