Top 30 Most Common Oops Interview Questions For Freshers You Should Prepare For
Written by
James Miller, Career Coach
Landing your first job as a software developer often requires demonstrating a solid understanding of core programming concepts. For many roles, especially those involving languages like Java, C++, C#, and Python, Object-Oriented Programming (OOP) is fundamental. Interviewers rely heavily on oops interview questions for freshers to gauge a candidate's foundational knowledge, problem-solving approach, and readiness to work with modern software design patterns. Preparing effectively for these questions is crucial for making a strong first impression. This guide provides a comprehensive list of the 30 most common oops interview questions for freshers, offering insights into why they are asked, how to structure your answers, and example responses to help you build confidence and succeed in your technical interviews. Mastering these concepts is not just about memorizing definitions but understanding how they apply in real-world coding scenarios. Let's dive into the essential OOP knowledge you need to ace those crucial early interviews.
What Are Oops Interview Questions For Freshers?
Oops interview questions for freshers are technical questions specifically designed to assess a candidate's understanding of the core principles of Object-Oriented Programming (OOP). These questions cover foundational concepts like classes, objects, encapsulation, abstraction, inheritance, and polymorphism. They aim to determine if a candidate grasps the 'why' behind OOP – its benefits for code organization, reusability, and maintainability – rather than just syntax. For freshers, these questions are particularly important because they test the theoretical foundation learned during academic studies or self-learning. Demonstrating a clear understanding of oops interview questions for freshers shows potential employers that you have the necessary groundwork to build upon and learn more advanced topics. They are the gateway to proving your basic programming literacy in an object-oriented context.
Why Do Interviewers Ask Oops Interview Questions For Freshers?
Interviewers ask oops interview questions for freshers for several key reasons. Firstly, they serve as a fundamental knowledge check. OOP is a dominant paradigm in many programming languages, and a basic grasp is essential for contributing to software projects. Secondly, these questions reveal a candidate's problem-solving approach; OOP principles often lead to more modular, scalable, and maintainable code, and interviewers want to see if freshers understand these benefits. Thirdly, discussing OOP concepts provides insight into a candidate's communication skills regarding technical topics. Explaining complex ideas clearly is vital for collaboration. Finally, mastering oops interview questions for freshers indicates a candidate's preparedness and seriousness about a career in software development, showing they have invested time in learning foundational computer science principles.
Preview List
What does OOPS stand for?
What are the four basic concepts of OOPS?
What is a class?
What is an object?
What is the difference between a class and an object?
What is encapsulation?
What is abstraction?
What is inheritance?
What is polymorphism?
What is a constructor?
What is the difference between method overloading and method overriding?
What are the types/subcategories of inheritance?
What is an interface?
What is the difference between an abstract class and an interface?
What is type casting in OOP?
What is cohesion?
What is coupling?
Difference between cohesion and coupling?
What is a destructor?
What is a static constructor?
What is a friend function?
What is an example of a virtual function?
What is method overriding?
What is method overloading?
What is a structure and how is it different from a class?
What is an example of polymorphism?
What makes OOP different from procedural programming?
What is abstraction vs polymorphism?
Why should you program to an interface?
How is an abstract class used in OOP?
1. What does OOPS stand for?
Why you might get asked this:
This is a basic test to ensure you know the full term for the acronym OOPS, which is fundamental to the entire discussion.
How to answer:
State the full form clearly and concisely.
Example answer:
OOPS stands for Object-Oriented Programming System or sometimes Object-Oriented Programming Structure. It's a programming paradigm centered around objects rather than functions and logic.
2. What are the four basic concepts of OOPS?
Why you might get asked this:
Interviewers check if you know the core pillars of OOP, which are the building blocks for understanding the paradigm.
How to answer:
List and briefly define each of the four main concepts: Encapsulation, Abstraction, Inheritance, and Polymorphism.
Example answer:
The four basic concepts are Encapsulation (bundling data and methods), Abstraction (hiding details), Inheritance (creating new classes from existing ones), and Polymorphism (objects taking many forms).
3. What is a class?
Why you might get asked this:
This tests your understanding of the fundamental blueprint used to create objects in OOP.
How to answer:
Define a class as a template or blueprint for creating objects, specifying their attributes (data) and behaviors (methods).
Example answer:
A class is essentially a blueprint or a template for creating objects. It defines the structure, specifying the data fields (attributes) and the methods (behaviors) that objects of that class will have.
4. What is an object?
Why you might get asked this:
This confirms you understand that objects are the actual instances created from a class blueprint, representing real-world entities.
How to answer:
Define an object as an instance of a class, possessing the properties and behaviors defined by its class.
Example answer:
An object is a concrete instance of a class. It's a real-world entity that has state (values for its attributes) and behavior (actions it can perform using its methods), created based on the class blueprint.
5. What is the difference between a class and an object?
Why you might get asked this:
This question assesses your grasp of the relationship between the template (class) and its concrete realization (object).
How to answer:
Explain that a class is the blueprint or definition, while an object is a specific instance created from that class. Use an analogy if helpful.
Example answer:
A class is a logical template that defines the properties and methods, like a cookie cutter. An object is a physical instance created from that template, like an actual cookie made with the cutter.
6. What is encapsulation?
Why you might get asked this:
This concept is key to data security and organization in OOP. Interviewers want to know if you understand bundling and data hiding.
How to answer:
Explain encapsulation as wrapping data and methods within a single unit (the class) and restricting direct access to the data. Mention data hiding.
Example answer:
Encapsulation is the mechanism of binding data (attributes) and the code that manipulates the data (methods) together into a single unit, which is typically the class. It also involves hiding the internal state of an object.
7. What is abstraction?
Why you might get asked this:
This tests your understanding of simplifying complexity by hiding implementation details and showing only necessary features.
How to answer:
Define abstraction as hiding complex implementation details and exposing only essential features or functionalities to the user.
Example answer:
Abstraction is about hiding complexity by showing only the necessary features of an object while concealing the intricate background details. Think of driving a car; you interact with the steering wheel and pedals, not the engine mechanics.
8. What is inheritance?
Why you might get asked this:
Inheritance is a core mechanism for code reuse and establishing relationships between classes.
How to answer:
Explain inheritance as a process where a new class (child/subclass) inherits properties and behaviors from an existing class (parent/superclass).
Example answer:
Inheritance is an OOP concept where a new class, called a subclass or derived class, inherits attributes and methods from an existing class, called a superclass or base class. This promotes code reusability and establishes an 'is-a' relationship.
9. What is polymorphism?
Why you might get asked this:
Polymorphism is crucial for flexibility and handling objects of different types through a common interface.
How to answer:
Define polymorphism as the ability of an object to take on many forms. Explain it typically manifests through method overloading (same name, different parameters) and method overriding (same name and parameters in child class).
Example answer:
Polymorphism means "many forms." In OOP, it allows you to perform a single action in different ways. It's primarily achieved through method overloading (same method name, different parameters) and method overriding (subclass providing specific implementation of a superclass method).
10. What is a constructor?
Why you might get asked this:
Constructors are vital for object initialization. Knowing this shows you understand how objects are brought to life.
How to answer:
Explain that a constructor is a special method within a class used to initialize objects when they are created.
Example answer:
A constructor is a special member function of a class that is automatically invoked whenever an object of that class is created. Its primary purpose is to initialize the object's attributes with initial values.
11. What is the difference between method overloading and method overriding?
Why you might get asked this:
This is a classic question testing your understanding of how polymorphism is implemented at compile-time vs. runtime.
How to answer:
Clearly distinguish between them: overloading is about having methods with the same name but different parameter lists in the same class; overriding is a subclass providing its implementation of a superclass method with the same signature. Mention compile-time vs. runtime.
Example answer:
Method overloading is Compile-Time Polymorphism; methods have the same name in the same class but different parameter lists. Method overriding is Runtime Polymorphism; a subclass provides a specific implementation for a method already defined in its superclass with the exact same signature.
12. What are the types/subcategories of inheritance?
Why you might get asked this:
This tests your broader knowledge of how classes can inherit from one another in various structures.
How to answer:
List common types of inheritance, such as single, multilevel, hierarchical, and hybrid. Mentioning multiple inheritance (if supported by the language) is a plus.
Example answer:
Common types include Single (one base class, one derived class), Multilevel (A inherits from B, C inherits from A), Hierarchical (Multiple classes inherit from one base class), and Hybrid (a mix of others).
13. What is an interface?
Why you might get asked this:
Interfaces are crucial for defining contracts and achieving abstraction and loose coupling.
How to answer:
Define an interface as a blueprint for a class, containing method signatures but no implementation. Explain it specifies a contract that implementing classes must follow.
Example answer:
An interface is a contract that defines a set of method signatures that a class must implement. It specifies 'what' a class should do, without specifying 'how' it should do it. It's used to achieve abstraction and support multiple inheritance-like behavior.
14. What is the difference between an abstract class and an interface?
Why you might get asked this:
This question evaluates your understanding of two key tools for abstraction and their distinct uses and capabilities.
How to answer:
Highlight key differences: abstract classes can have both abstract and concrete methods, contain fields (state), and have constructors, while interfaces only declare methods (no state) and are implemented.
Example answer:
An abstract class can have abstract (no implementation) and concrete (with implementation) methods, can have instance variables, and constructors. An interface can only have abstract methods (implicitly) and no instance variables; classes implement interfaces.
15. What is type casting in OOP?
Why you might get asked this:
Type casting is often used with inheritance and polymorphism, and understanding it is necessary for working with object hierarchies.
How to answer:
Explain type casting as converting an object of one type to another. Specifically mention upcasting (child to parent, always safe) and downcasting (parent to child, potentially unsafe, requires check).
Example answer:
Type casting is converting an object reference from one class type to another. Upcasting (e.g., Dog object to Animal reference) is implicit and safe. Downcasting (e.g., Animal reference to Dog object) is explicit and requires checking the actual object type to avoid errors.
16. What is cohesion?
Why you might get asked this:
Cohesion relates to how well elements within a single module or class belong together. High cohesion is desirable in good OOP design.
How to answer:
Define cohesion as the degree to which the elements within a module (like a class) belong together or are functionally related. High cohesion means a class has a single, well-defined responsibility.
Example answer:
Cohesion refers to the degree to which the elements inside a module or class are related to one another and contribute to a single, well-defined purpose. High cohesion is good as it indicates a class is focused and manageable.
17. What is coupling?
Why you might get asked this:
Coupling measures the interdependence between different modules or classes. Low coupling is a goal for flexible and maintainable systems.
How to answer:
Define coupling as the degree of interdependence between software modules or classes. Explain that low coupling means classes are independent, making changes easier.
Example answer:
Coupling is the degree of interdependence between different classes or modules. Low coupling means classes are relatively independent and interact through well-defined interfaces. High coupling makes systems harder to modify and maintain.
18. Difference between cohesion and coupling?
Why you might get asked this:
This question tests your ability to compare two related but distinct concepts critical for good software design.
How to answer:
Clearly state that cohesion focuses on internal relationships within a single module/class, while coupling focuses on external relationships between different modules/classes. Emphasize the goal: High cohesion, Low coupling.
Example answer:
Cohesion is about relationships within a class (how well its elements work together for one purpose). Coupling is about relationships between classes (how dependent they are on each other). Good design aims for high cohesion and low coupling.
19. What is a destructor?
Why you might get asked this:
Destructors handle object cleanup and resource release, showing an understanding of the object lifecycle. (More prominent in languages like C++).
How to answer:
Define a destructor as a special method called when an object is destroyed or goes out of scope. Explain its purpose is to free up resources allocated by the object.
Example answer:
A destructor is a special member function (primarily in C++) that is automatically called when an object is destroyed or leaves its scope. Its main purpose is to clean up resources like memory or file handles that the object used.
20. What is a static constructor?
Why you might get asked this:
This tests your knowledge of class-level initialization, distinct from object initialization. (More common in C#).
How to answer:
Explain that a static constructor initializes static members of a class. Note that it is called only once, before any instance is created or any static member is referenced.
Example answer:
A static constructor is used to initialize static data members of a class or to perform a particular action that needs to be performed only once for the class. It's called automatically before any instance is created or any static members are accessed.
21. What is a friend function?
Why you might get asked this:
Friend functions are a specific feature in C++ allowing non-member functions access to private/protected members. (Language-specific).
How to answer:
In the context of C++, define a friend function as a function declared outside a class but granted special permission to access the class's private and protected members.
Example answer:
In C++, a friend function is a function that is declared outside the class but is given special access permission to access the private and protected members of the class. It is not a member function of the class itself.
22. What is an example of a virtual function?
Why you might get asked this:
Virtual functions are fundamental to achieving runtime polymorphism (method overriding).
How to answer:
Describe a scenario with a base class and a derived class. Explain how declaring a method 'virtual' in the base class allows the derived class's overridden version to be called when using a base class pointer/reference pointing to a derived object.
Example answer:
Suppose a base Animal class has a virtual speak() method. A Dog class derived from Animal overrides speak(). If you have an Animal pointer pointing to a Dog object and call speak(), the Dog's speak method is executed thanks to the virtual function.
23. What is method overriding?
Why you might get asked this:
This reiterates understanding of a key polymorphism mechanism.
How to answer:
Explain that method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its parent class, using the same method signature.
Example answer:
Method overriding is when a subclass defines a method with the same name, parameters, and return type as a method already present in its superclass. This allows the subclass to provide its own specific implementation of that method.
24. What is method overloading?
Why you might get asked this:
This reiterates understanding of the other key polymorphism mechanism.
How to answer:
Explain that method overloading involves defining multiple methods within the same class that have the same name but different parameter lists (either in number, type, or order).
Example answer:
Method overloading is defining multiple methods within the same class that share the same name but differ in their signature, specifically the number or types of parameters they accept. This allows a single method name to perform different actions based on input.
25. What is a structure and how is it different from a class?
Why you might get asked this:
This explores differences in data grouping constructs, often language-dependent (e.g., C++ vs. C#).
How to answer:
Explain that structures also group data members, similar to classes. Highlight key differences which are often default access specifiers (structs often public, classes often private) and sometimes value vs. reference types (structs often value types).
Example answer:
A structure is similar to a class as it groups related data. The key difference varies by language; in C++, members are public by default in structs and private in classes. In C#, structs are value types stored on the stack, while classes are reference types on the heap.
26. What is an example of polymorphism?
Why you might get asked this:
This asks for a practical illustration of polymorphism in action, often involving inheritance and method overriding.
How to answer:
Provide a simple code example or scenario where a base class reference/pointer holds an object of a derived class, and calling a method on that reference executes the derived class's overridden method.
Example answer:
Consider a Shape base class with a draw() method, and derived Circle and Square classes that override draw(). A list of Shape objects holding Circle and Square instances can call draw() on each, and the correct Circle or Square draw() method will execute dynamically.
27. What makes OOP different from procedural programming?
Why you might get asked this:
This tests your understanding of the fundamental paradigm shift from focusing on procedures/functions to focusing on objects and data.
How to answer:
Explain that procedural programming focuses on sequences of instructions and functions operating on data, while OOP organizes code around objects that combine data and the methods that operate on that data. Mention OOP benefits like modularity and reuse.
Example answer:
Procedural programming centers around writing sequences of instructions and functions to perform tasks. OOP, however, organizes code around objects, which are entities combining data (attributes) and behavior (methods). OOP promotes modularity, reusability, and data protection.
28. What is abstraction vs polymorphism?
Why you might get asked this:
This requires you to differentiate two distinct OOP pillars and their roles.
How to answer:
Explain that abstraction is about simplifying complexity by hiding details and showing essentials. Polymorphism is about the ability of objects/methods to take on multiple forms or implementations, often used to handle different object types uniformly through a common interface.
Example answer:
Abstraction is about hiding complex implementation details and providing a simple interface (like a car's dashboard). Polymorphism is about using a single interface to represent different underlying types or behaviors (like a 'draw' function working differently for a Circle and a Square).
29. Why should you program to an interface?
Why you might get asked this:
This best practice question assesses your understanding of design principles promoting flexibility and maintainability.
How to answer:
Explain that programming to an interface (or a superclass) rather than a concrete implementation reduces coupling. It allows you to easily swap different implementations without changing the code that uses the interface/superclass.
Example answer:
Programming to an interface means your code interacts with objects via an interface type rather than a specific class type. This makes your code more flexible and loosely coupled, allowing you to easily substitute different implementations of that interface without modifying the calling code.
30. How is an abstract class used in OOP?
Why you might get asked this:
This checks your understanding of the practical application of abstract classes in creating base classes that cannot be instantiated directly but provide a common base for subclasses.
How to answer:
Explain that an abstract class is used to provide a common base or template for related subclasses. It can define common methods (some possibly abstract, requiring subclass implementation) and shared data, acting as a contract or partial blueprint.
Example answer:
An abstract class is used to define a common interface or base for a group of related classes. It cannot be instantiated itself but serves as a superclass from which other classes inherit. It often contains abstract methods that derived classes must implement, enforcing a structure.
Other Tips to Prepare for a Oops Interview Questions For Freshers
Beyond mastering the definitions and examples for oops interview questions for freshers, practical preparation is key. Firstly, practice coding simple examples for each concept in your preferred language (Java, Python, C++, C#). Write code for inheritance hierarchies, implement interfaces, and demonstrate polymorphism. This hands-on experience solidifies theoretical knowledge. As Steve Jobs said, "The only way to do great work is to love what you do." If you genuinely engage with the concepts, preparation feels less like a chore. Mock interviews, especially those focused on technical topics like oops interview questions for freshers, can significantly boost confidence and refine your articulation. Platforms like Verve AI Interview Copilot offer realistic practice scenarios tailored to specific roles and skill levels, including detailed feedback on your technical answers and explanations. Consider using Verve AI Interview Copilot (https://vervecopilot.com) to simulate common questions and practice explaining concepts clearly under pressure. Review your code and answers with others or use tools like Verve AI Interview Copilot to identify areas for improvement.
Frequently Asked Questions
Q1: What is the 'is-a' relationship in OOP?
A1: It describes inheritance, where a subclass 'is a' type of the superclass (e.g., Dog is an Animal).
Q2: What is the 'has-a' relationship?
A2: It describes composition/aggregation, where one class 'has a' reference to an object of another class (e.g., Car has an Engine).
Q3: Can a class inherit from multiple classes?
A3: Some languages (like C++) allow multiple inheritance; others (like Java) restrict it to single inheritance but allow implementing multiple interfaces.
Q4: Why is data hiding important in OOP?
A4: Data hiding protects data integrity by restricting direct external access, forcing interaction through defined methods (encapsulation).
Q5: What is dynamic binding?
A5: Dynamic binding (or late binding) is when the method call is resolved at runtime, typically used with polymorphism (method overriding).
Q6: What is static binding?
A6: Static binding (or early binding) is when the method call is resolved at compile time, typically used with method overloading or non-virtual methods.
