Top 30 Most Common Object Oriented Programming Questions You Should Prepare For
Written by
James Miller, Career Coach
Navigating technical interviews can feel daunting, especially when core concepts like object-oriented programming (OOP) are on the table. OOP is a fundamental paradigm in software development, and interviewers frequently probe candidates' understanding of its principles and application. Whether you're a junior developer or a seasoned engineer, a solid grasp of OOP concepts is essential. Preparing for common object oriented programming questions can significantly boost your confidence and performance. This guide covers the top 30 most frequently asked object oriented programming questions, offering concise, answer-ready explanations to help you ace your next interview.
What Are object oriented programming questions?
object oriented programming questions assess a candidate's knowledge of the OOP paradigm. This includes understanding core principles like encapsulation, abstraction, inheritance, and polymorphism, as well as related concepts such as classes, objects, interfaces, abstract classes, constructors, and design patterns. These questions aim to evaluate not just rote memorization but also the candidate's ability to apply OOP principles to design and structure code effectively. They are a standard part of technical interviews across various programming languages like Java, C++, Python, and C#, all of which heavily utilize OOP. Mastering these object oriented programming questions demonstrates a strong foundation in modern software design.
Why Do Interviewers Ask object oriented programming questions?
Interviewers ask object oriented programming questions for several key reasons. Firstly, they want to gauge your fundamental understanding of software design principles. OOP is widely used because it promotes code reusability, maintainability, and scalability. Assessing your knowledge of these concepts helps determine if you can write clean, organized, and efficient code. Secondly, object oriented programming questions reveal your problem-solving approach. OOP principles provide tools to model real-world problems and structure complex systems. Interviewers want to see if you can think in terms of objects, classes, and their interactions. Finally, these questions help evaluate your communication skills. Being able to clearly explain complex technical concepts is crucial for team collaboration. Preparing for these object oriented programming questions shows diligence and readiness for the role.
What does OOP stand for?
What are the four basic concepts of OOP?
What is a class?
What is an object?
Difference between class and object?
What is Encapsulation?
What is Abstraction?
Difference between abstraction and encapsulation?
What is Inheritance?
What are different types of inheritance?
What is Polymorphism?
Difference between method overloading and overriding?
What is cohesion and coupling?
Difference between class and structure?
What is an interface?
Difference between abstract class and interface?
What is a constructor?
What is constructor chaining?
What is a destructor?
What is static constructor?
What is meant by data hiding?
What is exception handling?
What is garbage collection?
What is multiple inheritance?
Difference between association, aggregation, and composition?
What is the Open-Closed Principle?
What is the Single Responsibility Principle?
What is the Observer design pattern?
Can you override a static method?
What is polymorphism difference from abstraction?
Preview List
1. What does OOP stand for?
Why you might get asked this:
This is a foundational question to ensure you know the basic terminology and can start discussing the core paradigm of object oriented programming questions.
How to answer:
State the full form of the acronym and briefly mention its core idea (objects, data, methods).
Example answer:
OOP stands for Object-Oriented Programming. It's a programming paradigm centered around "objects," which bundle data and methods, helping structure software design around these entities rather than just functions.
2. What are the four basic concepts of OOP?
Why you might get asked this:
Tests your knowledge of the fundamental pillars that define object oriented programming questions and differentiate it from other paradigms.
How to answer:
List and briefly explain Encapsulation, Abstraction, Inheritance, and Polymorphism.
Example answer:
The four main concepts are Encapsulation (bundling data and methods, restricting access), Abstraction (hiding details, showing essentials), Inheritance (acquiring properties from a parent), and Polymorphism (taking many forms).
3. What is a class?
Why you might get asked this:
Evaluates your understanding of the basic building block in object oriented programming questions: the blueprint for creating objects.
How to answer:
Define a class as a template or blueprint that specifies attributes (data) and methods (behavior).
Example answer:
A class is a blueprint or template used to create objects. It defines the structure (properties/attributes) and behavior (methods) that any object created from it will possess.
4. What is an object?
Why you might get asked this:
Checks if you understand the instance-level entity derived from a class, a core element in answering object oriented programming questions.
How to answer:
Define an object as an instance of a class, a concrete entity with actual data based on the class template.
Example answer:
An object is an instance of a class. It is a concrete realization of the class blueprint, existing in memory and holding specific values for the attributes defined by its class.
5. Difference between class and object?
Why you might get asked this:
Probes your clarity on the relationship between the abstract template (class) and its concrete instance (object) in object oriented programming questions.
How to answer:
Explain that a class is a definition/template, while an object is an instance created from that template, with memory allocation.
Example answer:
A class is a conceptual blueprint or template, defining attributes and methods. An object is a specific instance created from that class, occupying memory and holding actual data according to the class definition.
6. What is Encapsulation?
Why you might get asked this:
Assesses your grasp of a key OOP principle for data protection and organization, vital for object oriented programming questions.
How to answer:
Describe it as bundling data and methods within a single unit (class) and controlling access using modifiers. Mention data hiding.
Example answer:
Encapsulation is binding data (variables) and the methods that operate on that data into a single unit, like a class. It involves restricting direct access to components, often using access modifiers, protecting data integrity.
7. What is Abstraction?
Why you might get asked this:
Tests understanding of how OOP simplifies complexity by hiding unnecessary details, a frequent topic in object oriented programming questions.
How to answer:
Explain it as hiding implementation details and exposing only essential features or interfaces to the user.
Example answer:
Abstraction is the principle of hiding complex implementation details and showing only the necessary or relevant features to the user. It simplifies the view of an object or system, focusing on "what it does" rather than "how it does it".
8. Difference between abstraction and encapsulation?
Why you might get asked this:
Checks your ability to distinguish between two related but distinct OOP principles often confused in discussions about object oriented programming questions.
How to answer:
Explain that abstraction is about hiding complexity (what) and encapsulation is about bundling data/methods and controlling access (how).
Example answer:
Abstraction focuses on simplifying complexity by hiding implementation details, revealing only essential features. Encapsulation is about bundling data and methods together within a class and managing access to protect the data.
9. What is Inheritance?
Why you might get asked this:
Fundamental to OOP, inheritance questions assess your understanding of code reuse and hierarchical relationships in object oriented programming questions.
How to answer:
Define it as a mechanism where a new class (child) acquires properties and behaviors from an existing class (parent). Mention code reuse.
Example answer:
Inheritance is an OOP mechanism where a new class (subclass or child class) derives properties and behaviors (methods) from an existing class (superclass or parent class), promoting code reusability and establishing "is-a" relationships.
10. What are different types of inheritance?
Why you might get asked this:
Tests your knowledge of variations in how inheritance is structured across different languages, relevant for many object oriented programming questions.
How to answer:
List common types like single, multiple, multilevel, hierarchical, and hybrid, briefly describing each.
Example answer:
Common types include single (one parent), multiple (multiple parents - language dependent), multilevel (chain), hierarchical (one parent, multiple children), and hybrid (combination).
11. What is Polymorphism?
Why you might get asked this:
Crucial for flexible design, polymorphism is a key concept in most object oriented programming questions.
How to answer:
Explain it means "many forms," allowing objects of different classes to respond to the same method call in their own way. Mention overloading and overriding.
Example answer:
Polymorphism means "many forms." It's the ability of different objects to respond to the same method call in a way specific to their class. It includes compile-time (overloading) and run-time (overriding) forms.
12. Difference between method overloading and overriding?
Why you might get asked this:
A common point of confusion; distinguishing these shows clear understanding of polymorphism aspects in object oriented programming questions.
How to answer:
Explain overloading is same method name, different parameters in the same class. Overriding is same method signature, different implementation in a child class.
Example answer:
Method overloading occurs within a single class where multiple methods have the same name but different parameters. Method overriding happens in inheritance, where a child class provides a specific implementation for a method already defined in its parent class with the same signature.
13. What is cohesion and coupling?
Why you might get asked this:
These principles relate to module design quality, essential for writing maintainable OOP code and relevant to object oriented programming questions about structure.
How to answer:
Define cohesion as how related elements inside a module are, aiming for high. Define coupling as interdependence between modules, aiming for low.
Example answer:
Cohesion refers to the degree to which elements within a module belong together; high cohesion is good, meaning a module has a single, well-defined responsibility. Coupling is the degree of interdependence between different modules; low coupling is preferred for flexibility and maintainability.
14. Difference between class and structure?
Why you might get asked this:
Relevant in languages like C++ or C#; tests understanding of how OOP features apply differently to these constructs, useful for language-specific object oriented programming questions.
How to answer:
Explain classes support OOP features (inheritance, polymorphism) and are typically reference types. Structures are simpler, often value types, primarily for data grouping, with fewer OOP features.
Example answer:
Classes typically support full OOP features like inheritance and polymorphism and are usually reference types. Structures are simpler, often value types, primarily used for grouping small amounts of data, and have limited or no support for inheritance.
15. What is an interface?
Why you might get asked this:
Interfaces define contracts, a crucial concept for achieving abstraction and polymorphism in object oriented programming questions.
How to answer:
Define it as a contract or blueprint of method signatures that a class must implement, enforcing specific behavior.
Example answer:
An interface is a contract that defines a set of method signatures (and sometimes properties) that a class must implement. It specifies "what" a class must do, without defining "how," achieving abstraction and multiple inheritance-like behavior.
16. Difference between abstract class and interface?
Why you might get asked this:
A common comparison point; tests your understanding of their distinct roles in design, relevant to many object oriented programming questions about abstraction.
How to answer:
Explain abstract classes can have implemented and unimplemented methods and state; interfaces historically only had unimplemented methods (though this varies by language version) and no state. A class can implement many interfaces but inherit one abstract class.
Example answer:
Abstract classes can contain both abstract (unimplemented) and concrete (implemented) methods and can have member variables. Interfaces traditionally only contained abstract methods and no state (though this is evolving). A class can inherit only one abstract class but implement multiple interfaces.
17. What is a constructor?
Why you might get asked this:
Fundamental to object creation; understanding constructors is essential for answering object oriented programming questions about object lifecycle.
How to answer:
Define it as a special method called automatically when an object is created, used to initialize the object's state.
Example answer:
A constructor is a special method within a class that is automatically called when an object of that class is created. Its primary purpose is to initialize the object's state (its member variables).
18. What is constructor chaining?
Why you might get asked this:
Tests knowledge of how constructors can call each other, useful for reducing code duplication in object creation logic, relevant for object oriented programming questions.
How to answer:
Explain it as one constructor calling another constructor within the same class or a superclass to streamline initialization.
Example answer:
Constructor chaining is the process where one constructor calls another constructor. This can be within the same class (using this()) or calling a constructor in the superclass (using super()), helping to avoid code duplication during object initialization.
19. What is a destructor?
Why you might get asked this:
Relevant in languages with manual memory management (like C++) or for resource cleanup; less so in garbage-collected languages (like Java), but still pertinent to object lifecycle object oriented programming questions.
How to answer:
Define it as a special method called when an object is destroyed, primarily for cleanup tasks like releasing resources.
Example answer:
A destructor is a special method, primarily in languages like C++, that is automatically called when an object is destroyed or goes out of scope. It's used to perform cleanup operations, such as releasing dynamically allocated memory or closing resources.
20. What is static constructor?
Why you might get asked this:
Tests understanding of class-level initialization versus instance-level, important for managing shared resources, a common theme in object oriented programming questions.
How to answer:
Explain it initializes static members of a class and is called only once, before any instance is created or static members are accessed.
Example answer:
A static constructor is used to initialize static data members of a class. It is called automatically only once for a class, typically before the first instance is created or any static member is accessed.
21. What is meant by data hiding?
Why you might get asked this:
A direct application of encapsulation; tests understanding of access control and data protection in object oriented programming questions.
How to answer:
Explain it's restricting direct access to an object's data members, usually via access modifiers (private, protected), allowing access only through public methods.
Example answer:
Data hiding is the practice of restricting direct access to an object's internal data members, typically by marking them as private or protected. Access is then controlled through public methods (getters/setters), preventing external code from modifying data unexpectedly.
22. What is exception handling?
Why you might get asked this:
While not strictly an OOP concept, it's a crucial part of writing robust, object-oriented software, often included in broader object oriented programming questions about system design.
How to answer:
Describe it as a mechanism to manage runtime errors (exceptions) gracefully, preventing program crashes and allowing recovery, often using try-catch blocks.
Example answer:
Exception handling is a mechanism to deal with runtime errors or exceptional conditions that disrupt the normal flow of the program. It allows the program to catch these errors and handle them gracefully, preventing unexpected crashes, often using try-catch-finally blocks.
23. What is garbage collection?
Why you might get asked this:
Relevant in languages with automatic memory management; understanding it shows awareness of resource handling in OOP environments, often part of broader object oriented programming questions.
How to answer:
Explain it's the automatic process of identifying and reclaiming memory occupied by objects that are no longer referenced by the program.
Example answer:
Garbage collection is an automatic memory management process. It identifies objects that are no longer reachable or in use by the program and reclaims the memory they occupy, preventing memory leaks and simplifying memory management for the developer.
24. What is multiple inheritance?
Why you might get asked this:
Tests knowledge of a specific inheritance type, highlighting variations across languages and potential design complexities, useful for comparative object oriented programming questions.
How to answer:
Define it as a class inheriting directly from more than one parent class. Mention that its support varies by language (e.g., C++ supports it, Java uses interfaces).
Example answer:
Multiple inheritance is an OOP feature where a class can inherit attributes and behaviors from more than one parent class. Its direct support varies by language (e.g., C++ supports it, Java achieves similar flexibility through interfaces).
25. Difference between association, aggregation, and composition?
Why you might get asked this:
These concepts describe relationships between objects, fundamental to object-oriented design and often part of advanced object oriented programming questions.
How to answer:
Define association as a general relationship. Explain aggregation as a "has-a" relationship with independent component lifecycle (weak ownership). Define composition as a "has-a" relationship with dependent component lifecycle (strong ownership).
Example answer:
Association is a general term for a relationship between objects. Aggregation is a specific "has-a" relationship where the contained objects can exist independently of the container (e.g., a library has books). Composition is a stronger "has-a" relationship where the contained objects' lifecycle is dependent on the container (e.g., a house has rooms; rooms don't exist without the house).
26. What is the Open-Closed Principle?
Why you might get asked this:
A core SOLID principle; essential for designing extensible and maintainable OOP systems, frequently appearing in design-related object oriented programming questions.
How to answer:
State the principle: software entities should be open for extension but closed for modification. Explain its purpose (stability, preventing breaking existing code).
Example answer:
The Open-Closed Principle states that software entities (classes, modules, functions) should be open for extension, meaning new functionality can be added, but closed for modification, meaning the existing code should not be changed to add new features.
27. What is the Single Responsibility Principle?
Why you might get asked this:
Another core SOLID principle; vital for creating well-designed, maintainable classes, key to answering object oriented programming questions about class design.
How to answer:
State the principle: a class should have only one reason to change. Explain its purpose (focused responsibility, easier maintenance).
Example answer:
The Single Responsibility Principle states that a class should have only one reason to change. This means a class should ideally have only one job or responsibility, which leads to more cohesive, understandable, and maintainable code.
28. What is the Observer design pattern?
Why you might get asked this:
Tests knowledge of common OOP design patterns, showing practical application of OOP principles, relevant for advanced object oriented programming questions.
How to answer:
Describe it as defining a one-to-many dependency where subjects notify observers about state changes automatically. Mention its use (e.g., event handling).
Example answer:
The Observer pattern defines a one-to-many dependency between objects. A 'subject' object notifies multiple 'observer' objects whenever its state changes. This is commonly used in event handling systems or GUI programming where components need to react to changes in other components.
29. Can you override a static method?
Why you might get asked this:
A specific technical question about polymorphism and static members; tests understanding of method binding and scope, common in detailed object oriented programming questions.
How to answer:
Answer directly: No. Explain that static methods belong to the class, not instances, and overriding applies to instance methods in an inheritance hierarchy. Mention method hiding.
Example answer:
No, you cannot override a static method in OOP. Static methods belong to the class itself, not to instances, and overriding is a concept applied to instance methods within an inheritance hierarchy. A subclass can declare a static method with the same signature (hiding it), but this is not overriding.
30. What is polymorphism difference from abstraction?
Why you might get asked this:
Requires distinguishing two often intertwined concepts, showing nuanced understanding of OOP principles, common in conceptual object oriented programming questions.
How to answer:
Reiterate definitions: Abstraction is hiding complexity and showing essentials (what). Polymorphism is allowing one interface to represent multiple underlying forms (how).
Example answer:
Abstraction is about hiding implementation details and showing only necessary features, reducing complexity. Polymorphism is about the ability of different objects to respond to the same method call in different ways specific to their class type, allowing code to work with objects of different types through a common interface.
Other Tips to Prepare for a object oriented programming questions
Preparing for object oriented programming questions involves more than just memorizing definitions. Practice writing code that applies these principles. Implement small projects demonstrating inheritance, polymorphism, and encapsulation. Think about real-world scenarios and how you would model them using classes and objects. "The best way to learn is by doing," as the old saying goes. Review design patterns and understand how they leverage OOP concepts. Explain these concepts out loud to someone else or even to yourself – this helps solidify your understanding and improves your ability to articulate answers clearly during the interview. Consider using tools like Verve AI Interview Copilot, which can simulate interview environments and provide feedback on your technical explanations, including object oriented programming questions. As a wise mentor once told me, "Confidence comes from preparation." Leveraging resources like Verve AI Interview Copilot can help you feel more prepared and confident. Practice explaining the difference between concepts like abstract classes and interfaces, or aggregation vs. composition. For detailed practice on specific object oriented programming questions and real-time feedback, check out https://vervecopilot.com. Mastering object oriented programming questions requires both theoretical knowledge and practical application.
Frequently Asked Questions
Q1: What is the 'this' keyword in OOP?
A1: 'this' refers to the current instance of the class, used to access members or call constructors of the current object.
Q2: What is the 'super' keyword?
A2: 'super' refers to the parent class, used to access members or call constructors of the superclass from a subclass.
Q3: What are access modifiers?
A3: Keywords (like public, private, protected) that set the accessibility level for classes, methods, and variables.
Q4: What is an abstract method?
A4: A method declared in an abstract class without an implementation; subclasses must provide the implementation.
Q5: Can a class have multiple constructors?
A5: Yes, a class can have multiple constructors with different parameters (constructor overloading).
Q6: What is composition over inheritance?
A6: A design principle favoring aggregation/composition ("has-a") relationships over inheritance ("is-a") for better flexibility and loose coupling.
