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+--- Thread: OOP Interview Questions and Answers 2026 - Top 10 Object Oriented Programming Questio (/oop-interview-questions-and-answers-2026-top-10-object-oriented-programming-questio)
OOP Interview Questions and Answers 2026 - Top 10 Object Oriented Programming Questio - Admin - 03-21-2026
Object Oriented Programming is asked in every technical interview across all programming languages in 2026, from freshers to experienced developers. Whether you're interviewing for Java, Python, C++, or C# Developer roles at TCS, Infosys, Wipro, or FAANG, these top 10 OOP interview questions are must-know.
Keywords: OOP interview questions 2026, object oriented programming interview, OOPS concepts interview, polymorphism interview, inheritance interview
1. What are the four pillars of OOP?
Encapsulation wraps data and methods into a single unit, hiding internal state. Abstraction shows only essential features and hides complexity. Inheritance allows a class to acquire properties of another class. Polymorphism lets objects behave differently based on their type through method overloading and overriding.
2. What is the difference between Abstraction and Encapsulation?
Abstraction hides complexity by showing only relevant features to the user through abstract classes and interfaces. Encapsulation hides internal data by bundling it with methods and using access modifiers like private and protected. Abstraction is a design concept, encapsulation is an implementation technique.
3. Explain method overloading vs method overriding.
Overloading defines multiple methods with the same name but different parameters in the same class. It is compile-time polymorphism. Overriding redefines a parent class method in a child class with the same signature. It is runtime polymorphism. Overloading increases readability, overriding enables dynamic behavior.
4. What is the difference between abstract class and interface?
Abstract classes can have constructors, instance variables, and concrete methods alongside abstract methods. Interfaces define contracts with only abstract methods and constants (default methods since Java 8). A class can implement multiple interfaces but extend only one class. Use interfaces for capability contracts.
5. What are access modifiers and their scope?
Public is accessible everywhere. Private is accessible only within the class. Protected is accessible within the class and subclasses. Default/Package-private is accessible within the same package. Access modifiers enforce encapsulation and control visibility of class members for better security and design.
6. Explain the types of inheritance.
Single inheritance: one child extends one parent. Multilevel: child extends parent which extends grandparent. Hierarchical: multiple children extend one parent. Multiple inheritance: one child extends multiple parents (supported via interfaces in Java). Hybrid combines multiple types. Diamond problem arises in multiple inheritance.
7. What is the SOLID principle in OOP?
Single Responsibility: a class should have one reason to change. Open/Closed: open for extension, closed for modification. Liskov Substitution: subtypes must be substitutable for base types. Interface Segregation: prefer specific interfaces over general ones. Dependency Inversion: depend on abstractions, not concrete classes.
8. What is composition vs inheritance? When to use which?
Inheritance creates an is-a relationship where child inherits parent behavior. Composition creates a has-a relationship where a class contains instances of other classes. Composition provides more flexibility and loose coupling. Prefer composition over inheritance for code reuse. Use inheritance for genuine type hierarchies.
9. What are design patterns and name common ones?
Design patterns are reusable solutions to common software design problems. Creational: Singleton, Factory, Builder. Structural: Adapter, Decorator, Facade. Behavioral: Observer, Strategy, Command. Singleton restricts instantiation to one object. Factory creates objects without specifying exact class. Observer defines event subscription.
10. What is the difference between shallow copy and deep copy in OOP?
Shallow copy creates a new object but copies references to nested objects, so both original and copy share inner objects. Deep copy creates a completely independent copy of the object including all nested objects. Shallow copy is faster but changes to nested objects affect both. Deep copy is safer but more expensive.
Conclusion: OOP concepts form the foundation of software engineering interviews in 2026. Master the four pillars, SOLID principles, and design patterns to succeed.
Tags: #OOP #InterviewQuestions #ObjectOriented #SOLID #DesignPatterns #Programming #Polymorphism #OOP2026