What will be printed for this code? public class ExceptionOrder { public static void main(String[] args) { try { try { throw new RuntimeException("Inner"); } catch (Exception e) { throw new IOException("Outer"); } } catch (IOException e) { System.out

The correct answer is C: Compilation error. IOException is a checked exception and must be declared in method signature or caught. The inner catch throws IOException which isn't caught immediately.

What is the type inference mechanism in lambda expressions?

The correct answer is A: Compiler infers parameter types from functional interface and context. Compiler uses target type (functional interface) to infer parameter types. If context is clear, explicit types not needed: list.forEach(x -> ...).

What is the output of multi-level exception chaining? public class ChainTest { public static void main(String[] args) { try { try { throw new IOException("IO Error"); } catch (IOException e) { throw new RuntimeException("Runtime Error", e); } } catch

The correct answer is B: IOException. getCause() returns the IOException that was wrapped. getClass().getSimpleName() returns 'IOException'.

What is the purpose of using @Bean method parameters in Spring @Configuration classes?

The correct answer is D: Both A and C are correct. Method parameters in @Bean methods allow Spring to inject dependent beans and establish bean relationships, enabling dependency injection at bean creation time.

Which of these operations is guaranteed to be atomic in ConcurrentHashMap?

The correct answer is B: map.putIfAbsent(key, value);. putIfAbsent() is an atomic operation. Options A and C-D are compound operations that are not atomic and can have race conditions between checks and modifications.

Home

Home › Subjects › Java Programming › OOP in Java

Java Programming
OOP in Java

Java OOP, collections, multithreading

27 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 27

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.1 Hard OOP in Java

In a banking system, Account is a parent class with method withdraw(). SavingsAccount and CurrentAccount both override it. A programmer writes: List accounts = new ArrayList(); accounts.add(new SavingsAccount()); accounts.add(new CurrentAccount()); for(Account a : accounts) a.withdraw(1000); Which concept is primarily demonstrated here?

A Encapsulation

B Abstraction only

C Polymorphism and Runtime Binding

D Inheritance only

Correct Answer: C. Polymorphism and Runtime Binding

EXPLANATION

The same withdraw() call behaves differently for SavingsAccount and CurrentAccount based on the actual object type at runtime. This is polymorphism with runtime (dynamic) binding.

Test

Q.2 Hard OOP in Java

Which of the following correctly implements the Factory Design Pattern principle in OOP?

A Creating objects directly using 'new' keyword everywhere

B Using a separate class with static methods to create and return objects of different types

C Using inheritance to create a base factory class

D Making all constructors private

Correct Answer: B. Using a separate class with static methods to create and return objects of different types

EXPLANATION

The Factory Pattern uses a separate class (factory) with methods to create and return objects. This decouples object creation from usage.

Test

Q.3 Hard OOP in Java

A system has classes: Vehicle -> Car -> ElectricCar. If Vehicle.start() is overridden in Car and again in ElectricCar, what is the output of: Vehicle v = new ElectricCar(); v.start();

A Vehicle's start() executes

B Car's start() executes

C ElectricCar's start() executes

D Compilation error

Correct Answer: C. ElectricCar's start() executes

EXPLANATION

This demonstrates dynamic (runtime) polymorphism. The actual object type (ElectricCar) determines which method is called, not the reference type (Vehicle).

Test

Q.4 Hard OOP in Java

In Java 16+, which sealed class feature allows you to restrict which classes can extend a class?

A Using 'final' keyword on all methods

B Using 'sealed' keyword with 'permits' clause

C Using 'protected' access modifier on constructor

D Using package-private access on the class

Correct Answer: B. Using 'sealed' keyword with 'permits' clause

EXPLANATION

Java 17 introduced 'sealed' classes with the 'permits' clause to explicitly specify which classes can extend a sealed class, providing better control over inheritance.

Test

Q.5 Hard OOP in Java

You need to create a class that provides common functionality for all database operations (insert, update, delete). What is the best approach?

A Create an interface DatabaseOperations

B Create an abstract class with abstract methods

C Create a concrete class with final methods

D Create an abstract class with some concrete methods for common logic

Correct Answer: D. Create an abstract class with some concrete methods for common logic

EXPLANATION

An abstract class allows you to define both abstract methods (to be overridden) and concrete methods (shared implementation), which is ideal for this scenario.

Test

Q.6 Hard OOP in Java

What is the key difference between composition and inheritance in object design?

A Composition is always better than inheritance

B Inheritance represents 'is-a' relationship; composition represents 'has-a' relationship

C Composition cannot access private members

D Inheritance is only for abstract classes

Correct Answer: B. Inheritance represents 'is-a' relationship; composition represents 'has-a' relationship

EXPLANATION

Inheritance models an 'is-a' relationship (Dog is-an Animal), while composition models a 'has-a' relationship (Car has-an Engine). Composition is often preferred for flexibility.

Test

Q.7 Hard OOP in Java

Which feature of Java ensures that a child class can have a method with a wider return type than the parent class?

A Method Overloading

B Method Overriding with Covariant Return Types

C Runtime Polymorphism

D Method Hiding

Correct Answer: B. Method Overriding with Covariant Return Types

EXPLANATION

Covariant return types (Java 5+) allow a method to return a subtype of the parent class method's return type. For example, if parent returns Animal, child can return Dog (subclass of Animal).

Test

Q.8 Hard OOP in Java

What is the correct order of execution when you create an object in a multi-level inheritance hierarchy?

A Child constructor -> Parent constructor -> Grandparent constructor

B Grandparent constructor -> Parent constructor -> Child constructor

C All constructors execute simultaneously

D Only the child constructor executes

Correct Answer: B. Grandparent constructor -> Parent constructor -> Child constructor

EXPLANATION

Constructor execution follows the inheritance chain from top to bottom. super() is implicitly called, executing parent constructors first.

Test

Q.9 Hard OOP in Java

In a real-world e-commerce system, you want to prevent direct instantiation of a base Product class but allow creation of Laptop, Mobile, and Tablet. Which approach is best?

A Make Product class final

B Make Product class abstract with abstract methods for subclasses to implement

C Make Product class private

D Use an interface for Product

Correct Answer: B. Make Product class abstract with abstract methods for subclasses to implement

EXPLANATION

An abstract class with abstract methods enforces that subclasses must implement required behaviors while preventing direct instantiation of the base class.

Test

Q.10 Hard OOP in Java

What will be the compilation result of this code?
interface A { void method(); }
interface B { void method(); }
class C implements A, B {
public void method() { }
}

A Compilation error: ambiguous method

B Compiles successfully

C Runtime error

D Compilation error: method signature mismatch

Correct Answer: B. Compiles successfully

EXPLANATION

Java allows implementing multiple interfaces even if they have the same method signature. The class provides a single implementation that satisfies both interfaces. This compiles successfully.

Test

1 2 3

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming OOP in Java

Java Programming
OOP in Java