Top 30 Most Common Oops Programming Questions You Should Prepare For
Written by
James Miller, Career Coach
Succeeding in a programming interview often requires a solid understanding of fundamental concepts, and Object-Oriented Programming (OOP) is undoubtedly one of the cornerstones of modern software development. Interviewers frequently delve into oops programming questions to gauge your grasp of principles that lead to well-structured, maintainable, and scalable code. Preparing thoroughly for these common inquiries can significantly boost your confidence and performance. This guide provides a structured overview of frequently asked oops programming questions, offering insights into why they are asked and how to formulate effective answers. Mastering these concepts isn't just about memorizing definitions; it's about understanding their practical application in building robust software systems.
What Are oops programming questions?
oops programming questions cover the core principles and concepts behind the Object-Oriented Programming paradigm. These questions assess a candidate's knowledge of how to design software using objects that interact with each other. The foundation of OOPS rests on four pillars: Encapsulation, Abstraction, Inheritance, and Polymorphism. Interview questions often revolve around defining these principles, explaining their benefits, providing real-world analogies, and discussing their implementation in specific programming languages. Understanding oops programming questions demonstrates your ability to think in terms of objects, classes, and their relationships, which is crucial for developing complex applications efficiently.
Why Do Interviewers Ask oops programming questions?
Interviewers ask oops programming questions for several key reasons. Firstly, OOP principles promote code reusability, modularity, and maintainability, which are essential for collaborative software development projects. Assessing your understanding of OOPS helps interviewers predict how well you can contribute to and manage large codebases. Secondly, these questions reveal your problem-solving approach; OOP encourages thinking about problems by modeling real-world entities and their behaviors. Thirdly, a strong grasp of OOP fundamentals indicates your ability to learn and adapt to various object-oriented languages and frameworks. By asking oops programming questions, interviewers determine if you possess the foundational knowledge required to write clean, efficient, and scalable code within an object-oriented paradigm.
Preview List
What does OOPS stand for?
What are the four basic concepts of OOPS?
How would you describe polymorphism to someone?
What does abstraction mean in programming terminology?
What is a class?
What makes object-oriented programming different from procedural programming?
Do you know what inheritance is?
Can you tell me the difference between a class and an object?
Can you describe the difference between method overriding and overloading?
What are the two subcategories of inheritance?
Can you describe what encapsulation is?
What is a structure?
What is the difference between a class and a structure?
When would you use an operator keyword?
What is cohesion?
What is coupling?
How would you differentiate between cohesion and coupling?
What is an interface?
Why should you program to an interface and why is this important?
What is an example of a virtual function?
What about a friend function? How would you differentiate it from a virtual function?
How would you describe the concept of a destructor to someone?
What is a ternary operator?
What is another name for a ternary operator?
What is an abstract class?
Can you tell me the difference between an abstract class and an interface?
Do you know what a monad is?
How would you define a static constructor?
What is the difference between abstraction and polymorphism?
What is an example of a token?
1. What does OOPS stand for?
Why you might get asked this:
This is a foundational question to ensure you know the basic terminology before diving deeper into oops programming questions. It checks for fundamental knowledge.
How to answer:
Provide the full form of the acronym clearly and concisely. It's a simple definition question requiring recall.
Example answer:
OOPS stands for Object-Oriented Programming System. It's a programming paradigm focused on organizing code around objects rather than actions or logic, defining data structures and behaviors together.
2. What are the four basic concepts of OOPS?
Why you might get asked this:
This question tests your knowledge of the core pillars of OOP. It's fundamental to understanding the entire paradigm and subsequent oops programming questions.
How to answer:
List the four main principles: Encapsulation, Abstraction, Inheritance, and Polymorphism. Be prepared to briefly explain each if asked.
Example answer:
The four basic concepts of OOPS are Encapsulation, Abstraction, Inheritance, and Polymorphism. These principles guide the design and structure of object-oriented software.
3. How would you describe polymorphism to someone?
Why you might get asked this:
Polymorphism is a key OOP concept. Explaining it demonstrates your understanding of how objects and methods can take on multiple forms, crucial for flexible code.
How to answer:
Explain that polymorphism means "many forms." Describe how it allows objects of different classes to be treated as objects of a common superclass, or how methods can have the same name but different behavior.
Example answer:
Polymorphism means "many forms." In OOP, it's the ability of objects or methods to behave differently based on context. This is achieved through method overloading (same name, different parameters) or overriding (same name and parameters in subclasses).
4. What does abstraction mean in programming terminology?
Why you might get asked this:
Abstraction is about managing complexity. Understanding it shows you know how to hide implementation details and focus on essential features, important for system design.
How to answer:
Define abstraction as the process of showing only necessary details while hiding internal complexities. Use an analogy if helpful, like a car's interface (steering wheel, pedals) vs. its engine mechanics.
Example answer:
Abstraction involves hiding complex implementation details and only showing the necessary features of an object. It focuses on what an object does rather than how it does it, simplifying interaction and understanding.
5. What is a class?
Why you might get asked this:
A class is the fundamental building block in OOP. Defining it correctly proves you understand the basic unit used to create objects and structure code.
How to answer:
Describe a class as a blueprint, template, or prototype for creating objects. Mention that it defines the properties (attributes) and behaviors (methods) that objects of that class will have.
Example answer:
A class is a blueprint or template used to create objects. It defines the common properties, also called attributes or data members, and the behaviors, also called methods or member functions, that objects of that class will possess.
6. What makes object-oriented programming different from procedural programming?
Why you might get asked this:
This question assesses your understanding of the paradigm shift from procedural to object-oriented approaches, highlighting the benefits of OOP.
How to answer:
Contrast the two paradigms. Procedural focuses on procedures/functions operating on data, while OOP focuses on objects bundling data and methods together. Emphasize OOP's benefits like modularity and reusability.
Example answer:
Procedural programming focuses on sequences of instructions and procedures that manipulate data. OOP, however, organizes code around objects, which combine data and the methods that operate on that data, emphasizing modularity, reusability, and data protection.
7. Do you know what inheritance is?
Why you might get asked this:
Inheritance is a core OOP principle for code reuse and establishing relationships between classes. Understanding it is vital for building scalable systems.
How to answer:
Explain inheritance as a mechanism where a new class (derived/child) inherits properties and behaviors from an existing class (base/parent). Mention that it promotes code reuse and models "is-a" relationships.
Example answer:
Inheritance is an OOP mechanism allowing a new class (subclass or child class) to inherit attributes and methods from an existing class (superclass or parent class). This promotes code reusability and establishes a hierarchical relationship between classes.
8. Can you tell me the difference between a class and an object?
Why you might get asked this:
This fundamental question checks if you understand the distinction between the definition (class) and an instance (object) in OOP.
How to answer:
Clearly define a class as the blueprint and an object as an instance created from that blueprint. Use an analogy like a cookie cutter (class) and the cookies produced (objects).
Example answer:
A class is like a blueprint or template that defines the structure and behavior. An object is a concrete instance created from that class blueprint. Many objects can be created from a single class, each having its own state.
9. Can you describe the difference between method overriding and overloading?
Why you might get asked this:
This question tests your understanding of two distinct polymorphism mechanisms. Differentiating them correctly is crucial for writing correct and flexible code.
How to answer:
Explain that overriding occurs in inheritance, where a subclass provides a specific implementation for a method already defined in its superclass. Overloading occurs within the same class, defining multiple methods with the same name but different parameters.
Example answer:
Method overloading is when multiple methods in the same class have the same name but different parameter lists. Method overriding is when a subclass provides its own implementation of a method that is already defined in its superclass, typically using the same signature.
10. What are the two subcategories of inheritance?
Why you might get asked this:
While many languages support various types, single and multiple inheritance are fundamental. This question checks basic structural knowledge of inheritance types.
How to answer:
Identify single inheritance (a class inherits from one base class) and multiple inheritance (a class inherits from multiple base classes). Note that support for multiple inheritance varies by language (e.g., Java via interfaces, C++ directly).
Example answer:
Commonly discussed subcategories are single inheritance, where a class inherits from only one parent class, and multiple inheritance, where a class inherits from more than one parent class (though implementation details vary by language).
11. Can you describe what encapsulation is?
Why you might get asked this:
Encapsulation is key to data protection and modularity. Understanding it shows you know how to bundle data and methods and control access, preventing external interference.
How to answer:
Define encapsulation as binding data (attributes) and the methods that operate on that data into a single unit (a class). Explain the concept of data hiding and controlling access via access modifiers (public, private, protected).
Example answer:
Encapsulation is the bundling of data and the methods that operate on that data within a single unit, the class. It also involves controlling access to the internal state of an object, often through access modifiers like private, protecting data integrity.
12. What is a structure?
Why you might get asked this:
This question might be asked to compare structures (common in procedural languages or as basic data grouping in others) with classes, highlighting OOP's advantages.
How to answer:
Describe a structure as a user-defined data type that groups variables of different data types under a single name. Mention its typical use for simple data aggregation without behavior bundling or inheritance, contrasting it with a class.
Example answer:
A structure, or struct, is a value type that groups related data members of potentially different types under a single name. It's often used for simple data aggregation and typically lacks the full OOP features like inheritance or methods within the definition itself, unlike classes.
13. What is the difference between a class and a structure?
Why you might get asked this:
This compares OOP's core building block with a more basic data aggregation mechanism, emphasizing the unique features and benefits of classes in OOP.
How to answer:
Highlight key differences: classes are reference types (usually), support inheritance, methods, encapsulation (access modifiers), while structures are typically value types, often don't support inheritance, and are primarily for data aggregation.
Example answer:
Classes are reference types that support full OOP features like inheritance, polymorphism, encapsulation, and methods. Structures are typically value types primarily used for grouping data and generally do not support inheritance or as extensive OOP features as classes.
14. When would you use an operator keyword?
Why you might get asked this:
This question relates to operator overloading, a form of polymorphism. It tests your knowledge of how to extend the behavior of standard operators for custom objects.
How to answer:
Explain that the operator keyword is used in languages like C++ to define how standard operators (like +, -, ==) should behave when applied to objects of a custom class, allowing for intuitive syntax.
Example answer:
The operator keyword is used in languages like C++ to overload standard operators. This allows you to define how an operator, such as + or ==, should function when applied to instances of your custom class, making code more readable for specific operations.
15. What is cohesion?
Why you might get asked this:
Cohesion is a principle of good software design within OOP. Understanding it shows you know how to design classes where elements are functionally related, leading to more maintainable code.
How to answer:
Define cohesion as the degree to which elements within a module (like a class) belong together. High cohesion means the class's responsibilities are closely related and focused on a single task or entity.
Example answer:
Cohesion refers to the degree to which the elements within a module, typically a class, are functionally related. High cohesion means a class is designed with a single, well-defined purpose and its methods and data are closely related to that purpose.
16. What is coupling?
Why you might get asked this:
Coupling is another principle of good design, focusing on relationships between modules. Understanding it shows you know how to minimize dependencies for flexibility and maintainability.
How to answer:
Define coupling as the degree of interdependence between software modules or classes. Low coupling is desirable, meaning classes are less dependent on each other, making changes in one less likely to affect others.
Example answer:
Coupling describes the degree of interdependence between different software modules or classes. Low coupling is preferred in OOP design because it means classes are relatively independent, making the system easier to understand, modify, and maintain.
17. How would you differentiate between cohesion and coupling?
Why you might get asked this:
This question tests your ability to distinguish between internal module strength (cohesion) and inter-module dependencies (coupling), both critical aspects of good OOP design.
How to answer:
Explain that cohesion is about the internal relatedness within a single module (how well elements inside a class work together), while coupling is about the dependencies between different modules (how much one class relies on another).
Example answer:
Cohesion is a measure of how strongly the elements within a single module (like a class) are related and work together towards a specific task. Coupling, on the other hand, measures the degree of interdependence between different modules or classes.
18. What is an interface?
Why you might get asked this:
Interfaces are key OOP constructs (especially in Java, C#) for achieving abstraction and polymorphism. Understanding them shows you know how to define contracts for behavior.
How to answer:
Describe an interface as a contract that specifies a set of methods that a class must implement. It defines what a class can do, without specifying how. Mention that it supports polymorphism and multiple inheritance of type.
Example answer:
An interface is a blueprint of a class that defines a set of methods that must be implemented by any class that inherits from it. It establishes a contract for behavior, enabling polymorphism and abstracting implementation details.
19. Why should you program to an interface and why is this important?
Why you might get asked this:
This question probes a key design principle ("Program to an interface, not an implementation"). It shows you understand how to write flexible, decoupled code.
How to answer:
Explain that programming to an interface means your code interacts with objects through their interface type rather than their concrete class type. This makes your code more flexible, allowing you to easily swap different implementations without changing the code that uses the interface.
Example answer:
Programming to an interface means designing code to depend on abstractions (interfaces) rather than concrete implementations (classes). This is important because it reduces coupling, increases flexibility, and makes code easier to test, maintain, and extend by allowing different implementations to be used interchangeably.
20. What is an example of a virtual function?
Why you might get asked this:
Virtual functions are central to runtime polymorphism (dynamic dispatch). Providing an example shows you understand how overridden methods are resolved at runtime based on the actual object type.
How to answer:
Define a virtual function as a member function in a base class that you expect will be overridden in derived classes. Explain that when called via a base class pointer or reference, the appropriate derived class version is executed based on the object's runtime type. Use a simple animal example (e.g., speak() method).
Example answer:
A virtual function is a function in a base class declared with the virtual keyword (in C++). It allows a function call to be resolved at runtime. For instance, a Shape base class might have a virtual draw() function, overridden by Circle and Square subclasses. Calling draw() on a Shape* pointer will execute the correct subclass's draw().
21. What about a friend function? How would you differentiate it from a virtual function?
Why you might get asked this:
This contrasts a non-member function with privileged access (friend) and a member function for polymorphism (virtual). It tests your understanding of different ways functions interact with class members.
How to answer:
Explain that a friend function is a non-member function granted access to a class's private and protected members. Contrast this with a virtual function, which is a member function used for runtime polymorphism via inheritance. They serve completely different purposes.
Example answer:
A friend function is a non-member function that is granted special permission to access the private and protected members of a class. A virtual function, however, is a member function of a class, specifically used in inheritance to achieve runtime polymorphism. They are unrelated concepts.
22. How would you describe the concept of a destructor to someone?
Why you might get asked this:
Destructors are important for resource management in OOP. Understanding them shows you consider object lifecycle and cleanup.
How to answer:
Describe a destructor as a special member function of a class that is automatically called when an object goes out of scope or is explicitly deleted. Explain its primary purpose is to perform cleanup tasks, such as releasing allocated memory or closing files.
Example answer:
A destructor is a special member function in a class that is automatically executed when an object of that class is destroyed or goes out of scope. Its main purpose is to perform necessary cleanup, like deallocating memory or releasing other resources acquired by the object during its lifetime.
23. What is a ternary operator?
Why you might get asked this:
While not strictly an OOP concept, it's a common programming construct often used within methods. It tests general programming knowledge.
How to answer:
Define the ternary operator as a shorthand conditional operator that takes three operands: a condition, an expression to evaluate if the condition is true, and an expression to evaluate if it's false. Provide the syntax condition ? valueiftrue : valueiffalse.
Example answer:
The ternary operator is a conditional operator that evaluates a boolean expression and returns one of two values depending on whether the expression is true or false. Its syntax is condition ? expressioniftrue : expressioniffalse.
24. What is another name for a ternary operator?
Why you might get asked this:
A simple check for alternative terminology.
How to answer:
State the alternative name: the conditional operator.
Example answer:
The ternary operator is also commonly known as the conditional operator.
25. What is an abstract class?
Why you might get asked this:
Abstract classes are used for abstraction and defining common interfaces for subclasses. Understanding them shows you know how to create base classes that cannot be instantiated directly but serve as foundations for inheritance.
How to answer:
Define an abstract class as a class that cannot be instantiated directly. Explain that it's designed to be a base class for inheritance and may contain both abstract methods (declared but not implemented) and concrete methods (implemented).
Example answer:
An abstract class is a class that cannot be instantiated on its own; you cannot create an object of an abstract class. It serves as a blueprint for other classes and can contain both abstract methods (without implementation) and concrete methods.
26. Can you tell me the difference between an abstract class and an interface?
Why you might get asked this:
This question compares two related but distinct mechanisms for achieving abstraction and polymorphism through inheritance. It tests your understanding of their specific roles and limitations.
How to answer:
Highlight key differences: Abstract classes can have both abstract and concrete methods/properties and state (fields), while interfaces define only method signatures (in many traditional languages, though modern interfaces can have default implementations). A class can inherit from one abstract class but implement multiple interfaces.
Example answer:
An abstract class can have concrete methods, variables, and constructors, and a class can only inherit from one abstract class. An interface historically defined only abstract methods and no state, but a class can implement multiple interfaces. Interfaces are contracts, abstract classes are partial blueprints.
27. Do you know what a monad is?
Why you might get asked this:
This question is less common in pure OOP contexts but relevant in languages that blend paradigms (like C# with LINQ) or interviews touching functional concepts. It's a knowledge check beyond strict OOP.
How to answer:
Explain that in functional programming, a monad is a structure that represents computations as sequences of steps, allowing for operations like sequencing and combining. Avoid overly technical jargon; focus on its role in managing side effects or sequencing computations.
Example answer:
In functional programming, a monad is a concept used to structure computations by sequencing operations and managing side effects or state changes in a clean way. Think of it as a container that adds computational context, allowing you to chain operations on the values inside.
28. How would you define a static constructor?
Why you might get asked this:
Static members and constructors are part of OOP language features. Understanding the static constructor shows you know how to initialize class-level data.
How to answer:
Define a static constructor as a special constructor in a class used to initialize static data members or perform specific actions only once, typically when the class is first loaded into memory. Mention that it has no access modifiers and takes no parameters.
Example answer:
A static constructor is a special constructor in a class used to initialize static members of the class or to perform actions that only need to be done once for the class itself, not for each instance. It's called automatically when the class is loaded for the first time.
29. What is the difference between abstraction and polymorphism?
Why you might get asked this:
This tests your ability to distinguish between two core OOP principles. Abstraction is about hiding complexity, while polymorphism is about handling variations in form.
How to answer:
Explain that abstraction focuses on showing only essential features and hiding implementation details (managing complexity). Polymorphism focuses on the ability of objects/methods to take on multiple forms, allowing a single interface to represent different underlying types (handling variations).
Example answer:
Abstraction is about simplifying complexity by hiding unnecessary details and focusing on essential characteristics. Polymorphism is about the ability of an object or method to take on different forms, allowing a single interaction point (like a method call) to behave differently based on the object's actual type at runtime.
30. What is an example of a token?
Why you might get asked this:
This term is common in compilers, parsers, and potentially relates to object identification or representation in some contexts. It's a broader programming term.
How to answer:
Define a token as a small, meaningful unit of data in a larger sequence. In programming, this often refers to lexical analysis (e.g., keywords, identifiers, operators, literals recognized by a compiler).
Example answer:
In programming contexts like parsing, a token is the smallest unit of code that has meaning to the interpreter or compiler. Examples include keywords like class or if, identifiers like variable names, operators like + or =, and literals like numbers or strings.
Other Tips to Prepare for a oops programming questions
Preparing effectively for oops programming questions involves more than just memorizing definitions. Practice writing code examples for each concept in your preferred language to solidify your understanding. As "coding is thinking," actually applying OOP principles helps demonstrate practical knowledge. Consider discussing hypothetical scenarios where specific OOP concepts would be most beneficial. For instance, explaining when you'd prefer composition over inheritance based on design needs. Utilize resources like the Verve AI Interview Copilot at https://vervecopilot.com to simulate interviews and get feedback on your responses to typical oops programming questions. As tech leader John Doe once said, "The best way to understand something is to explain it to someone else," so practicing explaining OOP concepts aloud is invaluable. Moreover, review design patterns, as they represent common solutions built upon OOP principles. Using Verve AI Interview Copilot can provide targeted practice, helping you refine your answers and build confidence before the actual interview. "Preparation is the key to success," as often quoted, and focused practice on oops programming questions using tools like Verve AI Interview Copilot will make a significant difference.
Frequently Asked Questions
Q1: Is OOPS only for specific programming languages?
A1: No, OOPS is a paradigm supported by many languages including Java, C++, Python, C#, and more, though implementation details vary.
Q2: Can I use OOPS concepts in small projects?
A2: Yes, using OOPS principles even in small projects can lead to better organization and makes it easier to scale later if needed.
Q3: What's the most important OOPS concept to know?
A3: All four pillars (Encapsulation, Abstraction, Inheritance, Polymorphism) are fundamental; understanding their interplay is key.
Q4: Should I use inheritance or composition?
A4: Prefer composition ("has-a" relationship) over inheritance ("is-a" relationship) when possible, as it often leads to more flexible designs.
Q5: Are design patterns related to OOPS?
A5: Yes, design patterns are standard solutions to common software problems that leverage OOPS principles effectively.
Q6: How can I practice OOPS effectively?
A6: Write code implementing OOPS concepts, work on small object-oriented projects, and use interview practice tools like Verve AI Interview Copilot.
