Preparing for object oriented interview questions can feel daunting, but the payoff is huge. These questions show up in virtually every software-engineering, QA, or architecture interview because object-oriented skills sit at the heart of modern development. Mastering them not only boosts technical credibility but also signals to hiring managers that you can design maintainable, scalable systems. Before we dive in, remember: practice makes perfect. Verve AI’s Interview Copilot is your smartest prep partner—offering mock interviews tailored to tech roles. Start for free at https://vervecopilot.com.
What are object oriented interview questions?
Object oriented interview questions assess how well you understand and apply concepts such as classes, objects, inheritance, polymorphism, encapsulation, abstraction, SOLID, design patterns, memory management, and real-world modeling. Employers rely on these questions to confirm that you can translate customer requirements into clean, extensible code bases and that you know when to apply advanced design principles or keep things simple.
Why do interviewers ask object oriented interview questions?
Interviewers ask object oriented interview questions to gauge three things: conceptual depth, practical application, and communication clarity. They want evidence that you can reason about complex relationships, reduce coupling, enhance cohesion, and foresee maintenance challenges. Your answers reveal whether you have merely memorized definitions or truly internalized object-oriented thinking and can articulate trade-offs under pressure.
Preview List of the 30 Object Oriented Interview Questions
What does OOPS stand for?
What are the four basic concepts of OOPs?
What is Encapsulation?
What is Abstraction?
What is Inheritance?
What is Polymorphism?
What is a Class?
What is an Object?
What is the difference between a Class and an Object?
What is Multiple Inheritance?
What are the two subcategories of Inheritance?
What is Method Overloading?
What is Method Overriding?
What is the difference between Method Overloading and Method Overriding?
What is an Interface?
What is an Abstract Class?
What is the difference between an Abstract Class and an Interface?
What is Coupling?
What is Cohesion?
How would you differentiate between Cohesion and Coupling?
What are the SOLID Principles?
Why is it important to program to an Interface?
How is Memory Management handled in Java?
What is a Destructor?
How would you design an Inventory System using OOP principles?
How would you optimize an OOP-based e-commerce platform for high performance?
What is Dynamic Method Dispatch?
What are Delegates in C#? How are they used?
What is a Friend Function?
What is the difference between a Friend Function and a Virtual Function?
1. What does OOPS stand for?
Why you might get asked this:
Interviewers sometimes open with a straightforward definition to break the ice and verify that the candidate possesses baseline literacy in object oriented interview questions. By confirming you know that OOPS stands for Object-Oriented Programming System, they test whether you can anchor deeper concepts on a solid foundation and communicate clearly from the outset.
How to answer:
State the acronym confidently, then link it to its broader purpose—organizing software around objects rather than functions. Briefly mention key pillars such as encapsulation and abstraction, reinforcing that you’re ready for more advanced object oriented interview questions. Keep it crisp, direct, and jargon-free.
Example answer:
Sure. OOPS stands for Object-Oriented Programming System. The idea is that instead of structuring software purely around procedures, we model real-world entities as objects that carry both data and behavior. That approach improves modularity, eases maintenance, and makes it simpler to map features back to business concepts. Knowing the expansion shows I’m comfortable with the vocabulary, and it frames all the object oriented interview questions we’ll likely cover next.
2. What are the four basic concepts of OOPs?
Why you might get asked this:
This classic appears in many object oriented interview questions because it validates conceptual breadth. Interviewers want to see whether you can name and elaborate on encapsulation, abstraction, inheritance, and polymorphism without mixing them up, proving you grasp the pillars that everything else rests on.
How to answer:
List each concept, define it briefly, and offer a quick real-world analogy so the explanation sticks. Showing that you can translate theory into intuitive language hints at strong communication skills—crucial for team collaboration and mentoring.
Example answer:
The four pillars are encapsulation, abstraction, inheritance, and polymorphism. Encapsulation keeps an object’s state private, exposing only what callers need. Abstraction hides unnecessary detail so we interact at the right level, like driving a car without knowing every piston stroke. Inheritance lets us reuse and extend behavior—for example, a Truck class inheriting from Vehicle. Polymorphism allows one interface to trigger different behaviors, say drawing multiple shapes via a single draw() call. Understanding these principles is foundational for solving any advanced object oriented interview questions.
3. What is Encapsulation?
Why you might get asked this:
Hiring managers use this question to ensure you value information hiding, a technique that curbs unexpected side effects and streamlines maintenance. If you can articulate encapsulation well, they infer you’re less likely to create brittle, tightly coupled systems.
How to answer:
Explain that encapsulation bundles data and methods, restricts direct state access, and typically leverages access modifiers. Illustrate with a scenario—perhaps a BankAccount class safeguarding balance via getters and setters. Emphasize reduced risk and easier refactoring.
Example answer:
Encapsulation means wrapping an object’s state and the operations that modify that state inside a protective barrier. Take a BankAccount: we keep balance private and expose deposit or withdraw methods. No external class can set balance to a negative number directly; business rules live in one place. That discipline prevents rogue updates, simplifies debugging, and supports future changes such as currency conversion without breaking callers. It’s a practical technique I apply daily, and it regularly surfaces in object oriented interview questions because it’s the backbone of robust design.
4. What is Abstraction?
Why you might get asked this:
Abstraction reveals whether you understand layering—showing only what’s necessary and omitting clutter. Interviewers rely on this query to gauge if you can design APIs that clients find clear while still hiding messy internals.
How to answer:
Stress that abstraction focuses on the what, not the how. Provide an example like using a payment interface that processes cards, ACH, or PayPal without exposing cryptography details. Link to improved readability and maintainability.
Example answer:
Abstraction is about modeling the essence and ignoring extraneous mechanics. When users tap an e-commerce checkout button, they don’t care how tokenization works; they just need a charge() method. Internally we may hit different gateways, but the abstraction spares them the noise. I often create interface layers for this reason, and the principle shows up a lot in object oriented interview questions because it separates design excellence from verbose tangle.
5. What is Inheritance?
Why you might get asked this:
Inheritance remains pivotal yet risky if misused. By probing this, interviewers see if you understand code reuse, hierarchy design, and the pitfalls of deep inheritance trees.
How to answer:
Define inheritance, emphasize is-a relationships, note that composition can be favored, and illustrate with base and derived classes. Mention single, multilevel, and multiple inheritance variations where relevant.
Example answer:
Inheritance lets one class absorb properties and behaviors of another. For example, Dog inherits from Animal, automatically gaining breathing and movement traits while letting us override bark behaviors. It speeds up development but can lead to brittle chains if applied indiscriminately, so I weigh composition before extending hierarchies. Because design trade-offs matter, this topic pops up frequently in object oriented interview questions.
6. What is Polymorphism?
Why you might get asked this:
Polymorphism demonstrates dynamic flexibility—one interface, many implementations. Interviewers ask it to probe whether you can design extensible code that doesn’t require conditional explosions.
How to answer:
Explain compile-time (overloading) versus runtime (overriding). Offer a real scenario, like different Shape subclasses implementing draw(). Highlight reduced coupling.
Example answer:
Polymorphism lets the same call adapt to the actual object at runtime. Suppose you loop through a list of Shape objects and call draw(); each subclass renders appropriately—Circle adds arcs, Rectangle adds lines—without if-else chaos. That extensibility is why polymorphism is a staple among object oriented interview questions and why I rely on it for feature toggles without changing existing client code.
7. What is a Class?
Why you might get asked this:
Understanding what a class is seems trivial, yet slipping here signals shallow knowledge. Interviewers quickly verify that you see a class as a blueprint, not an object itself.
How to answer:
Define class as a template containing attributes and methods. Mention that it doesn’t occupy memory until instantiated. Link to how it enables modular design.
Example answer:
A class is a blueprint—think of architectural drawings for a house. The drawing lists dimensions and materials, but no real house exists until construction. Similarly, a class describes attributes and behaviors, like employeeName and calculatePay(). Only when I instantiate it does memory allocate for an actual object. Getting that nuance right is key for deeper object oriented interview questions where memory footprint matters.
8. What is an Object?
Why you might get asked this:
This pairs with the preceding class question. Interviewers ensure you grasp instantiation and runtime identity.
How to answer:
Define an object as a concrete instance with state and behavior that occupies memory during execution. Provide a quick example.
Example answer:
An object is the living embodiment of its class. If Class is the cookie cutter, an object is the cookie—actual dough with chocolate chips in a specific location. During runtime the object owns its own state, like balance = 200. Because interviews build up through layers, distinguishing class from object early prevents confusion in later object oriented interview questions.
9. What is the difference between a Class and an Object?
Why you might get asked this:
Even experienced devs occasionally mix terminology. Interviewers use this to test clarity in foundational vocabulary.
How to answer:
Contrast blueprint vs. instance, compile-time vs. runtime existence, and memory implications.
Example answer:
A class is the design spec; an object is the live entity. Think of a car factory. The engineering plans (class) describe wheel count, engine type, and features. When the assembly line finishes a vehicle, that specific car with VIN 12345 becomes an object. The plans exist once, but unlimited cars can be produced. Making this distinction crystal clear sets the stage for more advanced object oriented interview questions about instantiation costs or memory leaks.
10. What is Multiple Inheritance?
Why you might get asked this:
Multiple inheritance spurs debate about diamond problems and interface vs. implementation sharing. Interviewers use it to evaluate language-specific awareness.
How to answer:
Define multiple inheritance and specify how languages handle it—unsupported in Java for classes but emulated via interfaces, supported in C++. Discuss pros, cons, and conflict resolution.
Example answer:
Multiple inheritance allows a subclass to extend two or more parent classes, gaining behaviors from each. C++ supports it directly, but Java forbids class-level multiple inheritance to sidestep ambiguity—think two parents defining the same method. Instead, Java offers interfaces for type inheritance without implementation clash. Understanding when and how to employ multiple inheritance safely is crucial, which is why it features in many object oriented interview questions.
11. What are the two subcategories of Inheritance?
Why you might get asked this:
Differentiating single vs. multilevel inheritance reveals your command of class hierarchies. Interviewers look for tidy mental models rather than random memorization.
How to answer:
Explain single inheritance as one parent-one child, multilevel as grandparent-parent-child chains, and optionally touch on hierarchical or hybrid as bonus.
Example answer:
Two primary subcategories are single inheritance—where a class extends exactly one superclass—and multilevel inheritance, where Class C extends B, which in turn extends A, forming a chain. These distinctions impact complexity and method resolution order, so spotting them quickly helps me architect cleaner hierarchies and answer subsequent object oriented interview questions more accurately.
12. What is Method Overloading?
Why you might get asked this:
Overloading is compile-time polymorphism. Interviewers test if you understand signature rules and practical benefits like readability.
How to answer:
Define overloading, note that method names stay the same but parameter lists differ, and mention how the compiler picks the correct version.
Example answer:
Method overloading means defining several methods with identical names but different parameter types or counts—withdraw(int amount) vs. withdraw(float amount, String currency). At compile time the compiler resolves which version to call based on argument types. It clarifies intent, reducing mental overhead, which is why overloading surfaces often in object oriented interview questions about API design.
13. What is Method Overriding?
Why you might get asked this:
Overriding checks if you grasp runtime polymorphism, annotations like @Override, and Liskov compliance.
How to answer:
Explain that a subclass redefines a method with the same signature from its superclass to alter behavior. Reference dynamic dispatch.
Example answer:
When a subclass overrides, it supplies a new body for an inherited method, say calculateInterest(). The JVM decides at runtime which version to invoke based on actual object type. This lets SavingsAccount and CheckingAccount implement distinct interest rules. Mastering overriding is essential for open/closed adherence, so expect it in object oriented interview questions.
14. What is the difference between Method Overloading and Method Overriding?
Why you might get asked this:
Contrasting compile-time vs. runtime polymorphism shows depth. Interviewers want precise articulation under pressure.
How to answer:
Highlight signature variation, binding time, inheritance requirement, and purpose. Provide a quick table in words.
Example answer:
Overloading is within one class, differing by parameter signature, resolved at compile time, used for convenience. Overriding requires inheritance, same signature, resolved at runtime, used to customize behavior. Being able to compare them succinctly is common among object oriented interview questions because it validates full polymorphic understanding.
15. What is an Interface?
Why you might get asked this:
Interfaces embody abstraction and loose coupling. Interviewers want proof you can design for substitution and testability.
How to answer:
Define interface as a contract of abstract methods without implementation (until default methods in modern languages). Discuss multiple implementation benefit.
Example answer:
An interface is a contract that lists method signatures like connect(), send(), disconnect() for a MessagingClient. Any class—SMTP, SMS, Slack—can implement it. Callers depend on the interface, not the concrete class, which eases swapping. That’s why interfaces headline so many object oriented interview questions, especially when examining SOLID.
16. What is an Abstract Class?
Why you might get asked this:
Abstract classes blend partial implementation with enforced methods. Interviewers verify that you understand the mix and why you might prefer it to an interface.
How to answer:
Define, mention that abstract classes can have state and non-abstract methods, can’t instantiate directly, and commonly serve base template roles.
Example answer:
An abstract class is a partially complete blueprint. Consider an AbstractLogger that stores logLevel and provides a concrete timestamp() method while leaving writeMessage() abstract. Subclasses like FileLogger or CloudLogger fill in specifics. This structure balances reuse with flexibility, a nuance often tested via object oriented interview questions.
17. What is the difference between an Abstract Class and an Interface?
Why you might get asked this:
Differentiating these two is crucial. Interviewers judge whether you can choose the right tool and explain evolving language features.
How to answer:
Contrast implementation allowance, multiple inheritance capability, default visibility, and purpose.
Example answer:
An interface is pure behavior specification—historically no fields, just abstract methods, allowing a class to implement many interfaces. An abstract class can hold state, constructors, and partial implementation but supports only single inheritance in languages like Java. I pick an interface when I need role-based contracts; I choose an abstract class when shared code is considerable. Clarifying that distinction is central to many object oriented interview questions.
18. What is Coupling?
Why you might get asked this:
Coupling influences maintainability. Interviewers probe your design intuition.
How to answer:
Define coupling as dependency level between modules, explain tight vs. loose, and show why loose is better.
Example answer:
Coupling reflects how strongly one class relies on another. Tight coupling means changes ripple, like hard-coding concrete classes. Loose coupling employs interfaces or dependency injection so modules evolve independently. I constantly aim for low coupling to support future pivots, a theme that recurs in object oriented interview questions and real projects alike.
19. What is Cohesion?
Why you might get asked this:
Cohesion complements coupling. Interviewers gauge if you appreciate intra-class focus.
How to answer:
Define cohesion as how closely related responsibilities are within a unit. High cohesion is desirable.
Example answer:
Cohesion measures whether a class’s methods all revolve around a single purpose. A UserRepository that both queries DB and sends welcome emails has low cohesion. Splitting responsibilities improves readability. Because high cohesion simplifies maintenance, it remains a favorite among object oriented interview questions on design quality.
20. How would you differentiate between Cohesion and Coupling?
Why you might get asked this:
Comparative questions test clarity. Interviewers see if you can contrast inter- versus intra-module focus.
How to answer:
Describe cohesion as internal unity, coupling as external dependency, aim for high cohesion and low coupling, and give an analogy.
Example answer:
Cohesion is about how tightly a class’s own parts collaborate, whereas coupling is about how much one class leans on others. Imagine a well-organized toolbox: each drawer (class) holds related tools (high cohesion) and drawers don’t require opening other drawers to function (low coupling). Balancing both concepts guides my architecture choices and shows up often in object oriented interview questions.
21. What are the SOLID Principles?
Why you might get asked this:
SOLID acts as a universal design litmus test. Interviewers evaluate your commitment to maintainable code.
How to answer:
List all five: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion. Provide quick rationale.
Example answer:
SOLID stands for Single Responsibility (one reason to change), Open/Closed (open for extension, closed for modification), Liskov Substitution (subtypes maintain contract), Interface Segregation (prefer small focused interfaces), and Dependency Inversion (depend on abstractions). I apply SOLID to every feature; that’s why these principles dominate object oriented interview questions worldwide.
22. Why is it important to program to an Interface?
Why you might get asked this:
This question gauges your ability to create flexible, testable systems.
How to answer:
Explain decoupling, mockability, substitution, and future scalability.
Example answer:
Programming to an interface means clients rely on abstractions not implementations. I might code an OrderService to depend on PaymentGateway so I can plug Stripe or PayPal without altering business logic. Unit tests can inject a FakeGateway. This practice future-proofs code, hence its prominence in object oriented interview questions.
23. How is Memory Management handled in Java?
Why you might get asked this:
Memory safety impacts performance. Interviewers check if you understand garbage collection basics.
How to answer:
Describe automatic garbage collection, heap vs. stack, JVM tuning, and developer best practices like nulling references only when needed.
Example answer:
Java abstracts malloc/free via automatic garbage collection. Objects live on the heap, references on the stack. The JVM’s mark-and-sweep or generational collectors reclaim unreachable objects. I monitor GC logs and use tools like VisualVM to catch leaks. Knowing this lifecycle readies me for performance-centric object oriented interview questions.
24. What is a Destructor?
Why you might get asked this:
Languages differ in cleanup semantics. Interviewers check cross-language versatility.
How to answer:
Define destructor as a special method invoked when an object is about to be destroyed, usually to release resources. Mention C++, finalizers in .NET, and Java’s lack.
Example answer:
In C++ a destructor, marked with a tilde, runs when an object leaves scope, freeing memory or closing files. Managed languages automate memory, but you still implement IDisposable in C# for deterministic disposal. Understanding destructors’ role is critical for resource safety, explaining their appearance in object oriented interview questions.
25. How would you design an Inventory System using OOP principles?
Why you might get asked this:
Scenario questions reveal holistic design skills.
How to answer:
Outline core classes—Item, Inventory, Supplier, Order—show encapsulation, inheritance for Product variants, polymorphic pricing, and SOLID adherence.
Example answer:
I’d start with an abstract Product class storing SKU and price, extended by PerishableProduct or DigitalProduct. Inventory holds a collection of StockEntries encapsulating quantity and location. Services implement interfaces like ReorderPolicy to automate restocking. By injecting dependencies, I keep coupling low. This structure scales and shows how I apply theory from object oriented interview questions to real problems.
26. How would you optimize an OOP-based e-commerce platform for high performance?
Why you might get asked this:
They want proof you can balance OOP elegance with runtime speed.
How to answer:
Highlight caching, lazy loading, microservice break-out, and profiling.
Example answer:
First I’d profile to spot hotspots, then implement caching layers for product catalog reads. I’d decouple checkout into its own service to scale independently, use connection pooling, and apply polymorphic payment handlers so adding wallets doesn’t bloat logic. By combining design insight with performance metrics, I satisfy tough object oriented interview questions on scalability.
27. What is Dynamic Method Dispatch?
Why you might get asked this:
This checks runtime polymorphism understanding.
How to answer:
Explain that call resolution happens at runtime based on the object’s actual type, not reference type.
Example answer:
Dynamic method dispatch, or late binding, selects the overridden method corresponding to the object’s runtime class. If an Animal reference holds a Dog object, barking comes from Dog’s implementation. The JVM’s v-table handles lookup. Grasping this mechanism is critical for advanced object oriented interview questions exploring performance or design patterns like Visitor.
28. What are Delegates in C#? How are they used?
Why you might get asked this:
Delegates mix OO and functional concepts. Interviewers measure versatility.
How to answer:
Define delegate as a type-safe method pointer, discuss events and callbacks, and maybe mention Action/Func.
Example answer:
In C#, a delegate is an object that references methods with a particular signature, enabling callback patterns. I often wire a delegate to handle ButtonClick, decoupling UI from logic. Multicast delegates let multiple handlers respond. Knowing delegates equips me to answer cross-language object oriented interview questions confidently.
29. What is a Friend Function?
Why you might get asked this:
Friend functions are C++-specific. Interviewers assess language breadth.
How to answer:
Explain that friend functions can access private members of a class even though they aren’t members themselves, typically for operator overloading.
Example answer:
A friend function in C++ bypasses encapsulation to perform operations needing intimate access, like overloading << for output. I limit friends because they break information hiding. Discussing such nuances often arises in object oriented interview questions when the role involves legacy C++ codebases.
30. What is the difference between a Friend Function and a Virtual Function?
Why you might get asked this:
Contrast demonstrates nuanced comprehension of access vs. polymorphism.
How to answer:
Highlight friend for access control, virtual for runtime binding, and that friend isn’t polymorphic.
Example answer:
A friend function gains access privileges but remains external; it cannot be overridden. A virtual function lives inside a class hierarchy, supports polymorphism via v-tables, and respects overridability. Conflating them shows misunderstanding, which is why this distinction appears in challenging object oriented interview questions.
Other tips to prepare for a object oriented interview questions
Conduct weekly mock interviews with peers or tools like Verve AI Interview Copilot for instant, objective feedback.
Build mini-projects that exercise inheritance and polymorphism; teaching by doing cements knowledge.
Study design patterns, then refactor old code to apply them—seeing improvements firsthand builds talking points.
Create flashcards for SOLID, GRASP, and GOF patterns; spaced repetition locks in terminology for rapid recall during object oriented interview questions.
Record yourself answering; refine filler words and pacing.
You’ve seen the top questions—now it’s time to practice them live. Verve AI gives you instant coaching based on real company formats. Start free: https://vervecopilot.com. As Napoleon Hill said, “Strength and growth come only through continuous effort and struggle.” Treat each practice session as a step toward mastery.
Thousands of job seekers use Verve AI to land their dream roles. With role-specific mock interviews, resume help, and smart coaching, your object oriented interview questions just got easier. Start now for free at https://vervecopilot.com.
Frequently Asked Questions
Q1: How long should I spend preparing for object oriented interview questions?
A: Allocate at least two focused weeks, devoting daily time to definitions, design exercises, and mock interviews.
Q2: Do all companies ask object oriented interview questions?
A: Most software roles include them, though emphasis varies. Even startups value clean design discussions.
Q3: Are design patterns mandatory to mention?
A: Not mandatory, but weaving patterns into answers shows maturity and often impresses interviewers.
Q4: How do I avoid rote learning?
A: Apply each concept in a small project, then explain it aloud. Real usage beats memorization every time.
Q5: Can Verve AI Interview Copilot help with live interviews?
A: Yes. It offers AI-driven practice sessions, company-specific question banks, and real-time support so you feel calm and prepared when real object oriented interview questions arrive.
