Java · Question Set

OOP Deep Dive – Java interview questions

OOP Deep Dive interview questions for placements and exams.

Subject: JavaDifficulty: Mixed14 questions in this set

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Java – OOP Deep Dive questions (14)

Go through each question and its explanation. Use this set as a focused practice pack for Java.

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1. Name the four pillars of OOP in Java and give one-liner benefits for each.

Difficulty: EasyType: SubjectiveTopic: OOP Basics

Encapsulation (data safety), Abstraction (hide detail), Inheritance (reuse), Polymorphism (flexible behavior).

2. When would you choose an abstract class over an interface in modern Java?

Difficulty: MediumType: SubjectiveTopic: Interfaces

Abstract class for shared state/base implementation and ctor control; interface for capability types, multiple inheritance of behavior (default/static).

3. Which methods cannot be overridden?

Difficulty: MediumType: MCQTopic: Keywords

final forbids overriding; private isn’t visible to subclasses. static methods are hidden, not overridden.

4. Why are constructors not inherited? How does a subclass ensure proper initialization?

Difficulty: MediumType: SubjectiveTopic: Constructors

Constructors tie to class identity. Subclass chains initialization via super(...) call to construct the parent part first.

5. Pick the correct pairing:

Difficulty: EasyType: MCQTopic: Polymorphism

Overloading resolved at compile-time; overriding at runtime via dynamic dispatch.

6. What do sealed classes primarily control?

Difficulty: MediumType: MCQTopic: Sealed Types

sealed ... permits ... restricts the subclassing hierarchy for better design and exhaustiveness.

7. Give one scenario where composition is preferable to inheritance and explain why.

Difficulty: MediumType: SubjectiveTopic: OOP Design

Prefer composition to avoid tight coupling and fragile base class—e.g., reuse behavior by delegating to a helper instead of extending.

8. LSP implies a subtype should:

Difficulty: MediumType: MCQTopic: LSP

Clients coded to the base shouldn’t observe incorrect behavior when given the subtype.

9. Why is it dangerous to base equals/hashCode on mutable fields in a polymorphic class hierarchy?

Difficulty: MediumType: SubjectiveTopic: Equality

Mutations can break set/map invariants and lookup; cross-type symmetry/consistency can also be violated.

10. Dynamic method dispatch in Java selects the implementation based on:

Difficulty: MediumType: MCQTopic: Polymorphism

Overridden instance methods are chosen by the actual object type at runtime.

11. Differentiate Template Method and Strategy patterns in OOP terms.

Difficulty: MediumType: SubjectiveTopic: Patterns

Template Method fixes algorithm skeleton in a base class with overridable steps; Strategy composes behavior by swapping implementations at runtime.

12. Pick the correct statement:

Difficulty: EasyType: MCQTopic: OOP Keywords

this → current instance; super → immediate parent’s members/ctor.

13. Which is TRUE about method overriding?

Difficulty: EasyType: MCQTopic: Overriding

Overriding allows covariant return; access cannot be narrowed; static methods are hidden, not overridden.

14. A class implements two interfaces that define the same default method. How do you resolve the conflict?

Difficulty: MediumType: MCQTopic: Interfaces

Class must override and can delegate to a specific interface’s default via Interface.super.method().

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Java · Question Set

OOP Deep Dive – Java interview questions

OOP Deep Dive interview questions for placements and exams.

Subject: JavaDifficulty: Mixed14 questions in this set

Set overview

Questions

Included in this set

Subject

Java

Explore more sets

Difficulty

Mixed

Level of this set

Java – OOP Deep Dive questions (14)

Go through each question and its explanation. Use this set as a focused practice pack for Java.

Back to Java subject page

1. Name the four pillars of OOP in Java and give one-liner benefits for each.

Difficulty: EasyType: SubjectiveTopic: OOP Basics

Encapsulation (data safety), Abstraction (hide detail), Inheritance (reuse), Polymorphism (flexible behavior).

2. When would you choose an abstract class over an interface in modern Java?

Difficulty: MediumType: SubjectiveTopic: Interfaces

Abstract class for shared state/base implementation and ctor control; interface for capability types, multiple inheritance of behavior (default/static).

3. Which methods cannot be overridden?

Difficulty: MediumType: MCQTopic: Keywords

final forbids overriding; private isn’t visible to subclasses. static methods are hidden, not overridden.

4. Why are constructors not inherited? How does a subclass ensure proper initialization?

Difficulty: MediumType: SubjectiveTopic: Constructors

Constructors tie to class identity. Subclass chains initialization via super(...) call to construct the parent part first.

5. Pick the correct pairing:

Difficulty: EasyType: MCQTopic: Polymorphism

Overloading resolved at compile-time; overriding at runtime via dynamic dispatch.

6. What do sealed classes primarily control?

Difficulty: MediumType: MCQTopic: Sealed Types

sealed ... permits ... restricts the subclassing hierarchy for better design and exhaustiveness.

7. Give one scenario where composition is preferable to inheritance and explain why.

Difficulty: MediumType: SubjectiveTopic: OOP Design

Prefer composition to avoid tight coupling and fragile base class—e.g., reuse behavior by delegating to a helper instead of extending.

8. LSP implies a subtype should:

Difficulty: MediumType: MCQTopic: LSP

Clients coded to the base shouldn’t observe incorrect behavior when given the subtype.

9. Why is it dangerous to base equals/hashCode on mutable fields in a polymorphic class hierarchy?

Difficulty: MediumType: SubjectiveTopic: Equality

Mutations can break set/map invariants and lookup; cross-type symmetry/consistency can also be violated.

10. Dynamic method dispatch in Java selects the implementation based on:

Difficulty: MediumType: MCQTopic: Polymorphism

Overridden instance methods are chosen by the actual object type at runtime.

11. Differentiate Template Method and Strategy patterns in OOP terms.

Difficulty: MediumType: SubjectiveTopic: Patterns

Template Method fixes algorithm skeleton in a base class with overridable steps; Strategy composes behavior by swapping implementations at runtime.

12. Pick the correct statement:

Difficulty: EasyType: MCQTopic: OOP Keywords

this → current instance; super → immediate parent’s members/ctor.

13. Which is TRUE about method overriding?

Difficulty: EasyType: MCQTopic: Overriding

Overriding allows covariant return; access cannot be narrowed; static methods are hidden, not overridden.

14. A class implements two interfaces that define the same default method. How do you resolve the conflict?

Difficulty: MediumType: MCQTopic: Interfaces

Class must override and can delegate to a specific interface’s default via Interface.super.method().

More sets in Java

Core Java & JVM Basics(14+ Questions)
OOP Pillars(14+ Questions)
Strings & Core Collections Essentials(14+ Questions)
Exceptions & Error Handling in Java(14+ Questions)
Collections & Generics (Advanced)(14+ Questions)
Concurrency, Executors & Locks (Advanced)(14+ Questions)
Java Memory Model, GC & Performance Tuning(14+ Questions)
Java Streams & Functional Programming(15+ Questions)
Java Concurrency & Executors(13+ Questions)
Java I/O, NIO.2 & Serialization(14+ Questions)

Explore related subjects

HTML CSS Javascript Typescript SQL & Databases React

Continue your preparation

For complete preparation, combine this set with full subject-wise practice for Java. You can also explore other subjects and sets from the links below.

Quick navigation:Java subject page•All subjects

OOP Deep Dive – Java interview questions

Set overview

1. Name the four pillars of OOP in Java and give one-liner benefits for each.

2. When would you choose an abstract class over an interface in modern Java?

3. Which methods cannot be overridden?

4. Why are constructors not inherited? How does a subclass ensure proper initialization?

5. Pick the correct pairing:

6. What do sealed classes primarily control?

7. Give one scenario where composition is preferable to inheritance and explain why.

8. LSP implies a subtype should:

9. Why is it dangerous to base equals/hashCode on mutable fields in a polymorphic class hierarchy?

10. Dynamic method dispatch in Java selects the implementation based on:

11. Differentiate Template Method and Strategy patterns in OOP terms.

12. Pick the correct statement:

13. Which is TRUE about method overriding?

14. A class implements two interfaces that define the same default method. How do you resolve the conflict?

More sets in Java

Explore related subjects

Continue your preparation

Master Interviews Anywhere, Anytime

OOP Deep Dive – Java interview questions

Set overview

1. Name the four pillars of OOP in Java and give one-liner benefits for each.

2. When would you choose an abstract class over an interface in modern Java?

3. Which methods cannot be overridden?

4. Why are constructors not inherited? How does a subclass ensure proper initialization?

5. Pick the correct pairing:

6. What do sealed classes primarily control?

7. Give one scenario where composition is preferable to inheritance and explain why.

8. LSP implies a subtype should:

9. Why is it dangerous to base equals/hashCode on mutable fields in a polymorphic class hierarchy?

10. Dynamic method dispatch in Java selects the implementation based on:

11. Differentiate Template Method and Strategy patterns in OOP terms.

12. Pick the correct statement:

13. Which is TRUE about method overriding?

14. A class implements two interfaces that define the same default method. How do you resolve the conflict?

More sets in Java

Explore related subjects

Continue your preparation

Master Interviews
Anywhere, Anytime