Consider a scenario where you have an interface Shape with a method calculateArea(). You implement this in classes Circle and Rectangle. Which OOP concept is being demonstrated?

The correct answer is D: Both Abstraction and Polymorphism. The interface provides abstraction by hiding implementation details. Multiple classes implementing the same interface method demonstrates polymorphism (many forms).

What will be the output? class Test { int x = 5; { x = 10; } Test() { x = 15; } public static void main(String[] args) { Test t = new Test(); System.out.println(t.x); } }

The correct answer is C: 15. Instance initializer block executes after variable initialization but before constructor. Constructor executes last, setting x = 15.

Which of these correctly demonstrates the Producer Extends Consumer Super (PECS) principle?

The correct answer is A: public void process(List. PECS principle: use 'extends' when reading from a collection (source), use 'super' when writing to it (dest). Option A reads from source and writes to dest correctly.

Consider: interface I1 { void method(); } interface I2 { void method(); } class C implements I1, I2 { public void method() { System.out.println("Method"); } } What will be the behavior?

The correct answer is B: The single method implementation satisfies both interfaces. When a class implements multiple interfaces with the same method signature, a single method implementation satisfies all interfaces. This is resolved at compile time.

What is the underlying data structure of HashMap in Java?

The correct answer is B: Hash Table with Buckets. HashMap uses a hash table with buckets (arrays of linked lists or red-black trees) to store key-value pairs for efficient O(1) average lookup time.

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Java Programming

Java OOP, collections, multithreading

270 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 81–90 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.81 Easy JDBC

What exception is thrown when a database connection fails in JDBC?

A IOException

B SQLException

C ClassNotFoundException

D NullPointerException

Correct Answer: B. SQLException

EXPLANATION

SQLException is thrown when database-related errors occur, including connection failures and SQL execution errors.

Test

Q.82 Easy JDBC

Which method is used to retrieve the next row from a ResultSet?

A getNext()

B next()

C moveToNext()

D fetchNext()

Correct Answer: B. next()

EXPLANATION

The next() method moves the cursor to the next row in the ResultSet and returns true if a row exists.

Test

Q.83 Easy JDBC

What is the correct syntax to load a JDBC driver in Java?

A DriverManager.loadDriver('com.mysql.jdbc.Driver');

B Class.forName('com.mysql.jdbc.Driver');

C Driver.load('com.mysql.jdbc.Driver');

D Connection.loadDriver('com.mysql.jdbc.Driver');

Correct Answer: B. Class.forName('com.mysql.jdbc.Driver');

EXPLANATION

Class.forName() is the standard way to load JDBC drivers. It dynamically loads the driver class.

Test

Q.84 Easy JDBC

Which JDBC API is used to execute parameterized queries safely?

A Statement

B PreparedStatement

C ResultSet

D MetaData

Correct Answer: B. PreparedStatement

EXPLANATION

PreparedStatement allows parameterized queries using placeholders (?) and prevents SQL injection attacks.

Test

Q.85 Easy JDBC

Which interface in JDBC is used to execute SQL queries and retrieve results?

A Statement

B Connection

C ResultSet

D Driver

Correct Answer: A. Statement

EXPLANATION

Statement interface is used to execute SQL queries. Connection creates statements, ResultSet holds results, and Driver manages connections.

Test

Q.86 Easy JDBC

What is the purpose of the Connection.commit() method in JDBC?

A To establish a new database connection

B To permanently save all changes made in the current transaction

C To execute the next SQL statement

D To close the database connection

Correct Answer: B. To permanently save all changes made in the current transaction

EXPLANATION

commit() finalizes the transaction and persists all changes made since the last commit or rollback.

Test

Q.87 Easy JDBC

In JDBC, which exception is thrown when the database driver class is not found?

A SQLException

B ClassNotFoundException

C DriverNotFoundException

D DatabaseException

Correct Answer: B. ClassNotFoundException

EXPLANATION

ClassNotFoundException is thrown when Class.forName() cannot locate the JDBC driver class.

Test

Q.88 Easy JDBC

What does the DriverManager.getConnection() method return?

A A Statement object

B A Connection object

C A ResultSet object

D A DatabaseMetaData object

Correct Answer: B. A Connection object

EXPLANATION

DriverManager.getConnection() establishes a connection to the database and returns a Connection object.

Test

Q.89 Easy JDBC

Which JDBC method is used to retrieve the number of rows affected by an INSERT, UPDATE, or DELETE statement?

A getRowCount()

B executeUpdate()

C getUpdateCount()

D fetchSize()

Correct Answer: B. executeUpdate()

EXPLANATION

executeUpdate() returns an int representing the number of rows affected by the SQL statement execution.

Test

Q.90 Easy JDBC

What is the primary advantage of using PreparedStatement over Statement in JDBC?

A Better performance and protection against SQL injection

B Ability to execute multiple queries simultaneously

C Automatic connection pooling

D Direct transaction management

Correct Answer: A. Better performance and protection against SQL injection

EXPLANATION

PreparedStatement pre-compiles SQL and uses parameterized queries, preventing SQL injection and improving performance.

Test

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