OOP (Object-oriented Programming) is a programming paradigm that contains objects and fields to hold the data and methods to implement business logic. Every object can interact with other objects based on their access level modifiers. The object-oriented paradigm is based on classes and objects, where objects are instances of classes and can be created in various ways. There are various object-oriented programming languages, such as C++, C#, PHP, Ruby, Java, and Python. The main features of Object-oriented Programming techniques are Abstraction, Encapsulation, Inheritance, and Polymorphism. Most of the dynamic programming languages are based on OOP principles.
Now, if you are looking for a job related to OOP, you need to prepare for the 2026 OOP Interview Questions. Every interview is different for different job profiles, but to clear the interview, you need to have a good, clear understanding of OOP. Here, we have compiled important OOP Interview Questions and Answers to help you succeed in your interview. These OOP Interview questions are divided into parts as follows:
Below are the 10 important 2026 OOP Interview Questions and Answers:
OOP Interview Questions (Basic)
This first part covers basic OOP Interview Questions and Answers.
Q1. What are the core concepts of OOP?
Answer:
The core concepts of OOP are Abstraction, Encapsulation, Inheritance, and Polymorphism. Abstraction is the process of concealing the complex logic by defining the code in a separate private method, hiding its implementation. Any functionality needed can be called with its method identifier to get the result.
The concept of encapsulation is simply a Class used to hide the fields that hold data and the methods that perform functions, with access determined by the access modifier. Polymorphism is the process of defining the same method multiple times to utilize based on data types or arguments. There are two types of polymorphism: runtime and compile-time.
Q2. What is a Class in OOP?
Answer:
A Class in Object-oriented Programming is ideally called a template or a blueprint of an object. An object of its class type will have the same properties as defined in the implementation of Class. An object will always be a specific instance of a class. A Class can have different subclasses and superclasses. A class can be a child class or a parent class, depending on its declaration. A subclass can inherit all the properties of its superclass, whereas the superclass cannot inherit the subclass’s properties. Another class can extend a class, and the extended Class is called the parent class.
Let us move on to the next set of OOP Interview Questions and Answers.
Q3. What is a constructor in OOP?
Answer:
A constructor is a method used to invoke the object creation process by initializing the object’s state. The constructor name should ideally be the class name and may vary depending on the programming language. A constructor must not have any return type.
Q4. What is the Destructor in OOP?
Answer:
These are the most common OOP interview questions. A Destructor is a method that is invoked when an object is destroyed or when its scope ends. The method will be called explicitly or implicitly based on the programming language used. In C++, the destructor must be called, whereas in Java, it is not needed; the garbage collection mechanism handles it.
Q5. What is an Abstract class in OOP?
Answer:
An abstract class defines at least one abstract method, and objects cannot be created from it. Classes created using abstract classes are called derived classes. An abstract class will not contain implementation code in its base class. If an abstract class is instantiated, a compilation error will be thrown.
OOP Interview Questions (Advanced)
Let us now have a look at the advanced OOP Interview Questions.
Q6. What is multiple inheritance in OOP?
Answer:
Multiple inheritance is the process of extending the behaviors of multiple classes by a single class. It creates an ambiguous situation when the runtime has to decide which Class’s behavior to execute. C++ supports multiple inheritance, whereas Java doesn’t. The ambiguity and complexity create a diamond problem, defined as the issue of which parent class to extend when extending multiple classes.
Q7. What is static and dynamic binding in OOP?
Answer:
Static binding, also called early binding, occurs at compile time, whereas Dynamic binding, also called late binding, occurs at runtime. An example of static binding is method overloading, and an example of dynamic binding is method overriding. Binding for static, final, and private methods is always done at compile time, whereas overriding is done at runtime. The process of binding overloaded methods is called static, whereas the binding of overridden methods is called dynamic.
Let us move on to the next set of OOP Interview Questions and Answers.
Q8. What is operator overloading in OOP?
Answer:
Operator overloading is sometimes called ad-hoc polymorphism, which is defined as different operators having different mechanisms based on operator placement and arguments. In operator overloading, the semantics of the programming language are redefined, which is generally not recommended. In the case of the Java programming language, the creators decided not to use this feature, as Java is primarily a production language.
Q9. What is exception handling in OOP?
Answer:
These are the frequently asked OOP interview questions. Exception handling is a feature available in most object-oriented programming languages, defined as the process of handling exceptions during program execution. The flow of execution should be altered based on the outcome of the exception of aroused. The basic blocks of exception handling include try, catch, and throw in most programming languages, such as C++ and Java. In the try block, the code to be executed goes; the catch block handles the exception; and the thrown block returns the exception type and error if it can’t be handled. This is the safest way to handle applications and safeguard the flow of the working application.
Q10. What are the benefits of OOPS techniques?
Answer:
The main benefits of OOP concepts are modularity, extensibility, simplicity, reusability, maintainability, and modifiability. The complexity of the programming can be reduced, and the coding structure can be made clear. The various complex functionalities can be decoupled using distinct classes and implementation methods throughout the application. The reusability feature allows minor changes to the code as needed, providing adaptability for changes in code or functionality.
Objects from different classes can be reused in other implementation classes to fully leverage their features. The maintenance process becomes easier if the code is organized.
Q11. What is the difference between Composition and Inheritance?
Answer:
Composition and inheritance are two ways to reuse code in object-oriented programming. Inheritance represents an “is-a” relationship, such as a Car is a Vehicle, where a child class inherits properties and methods from a parent class. Composition represents a “has-a” relationship, such as a Car has an Engine, where one object contains another. Composition is often preferred because it offers greater flexibility and lower coupling, making code easier to modify, test, and maintain.
Q12. What is the SOLID principle in OOP?
Answer:
SOLID is a set of five object-oriented design principles that help developers write clean, flexible, and maintainable code. These principles improve code readability, reduce dependencies, and make applications easier to test, extend, and modify without affecting existing functionality. Following SOLID leads to better software design and long-term maintainability.
SOLID is a set of five object-oriented design principles that help developers create clean, maintainable, and scalable software.
- S – Single Responsibility Principle
- O – Open/Closed Principle
- L – Liskov Substitution Principle
- I – Interface Segregation Principle
- D – Dependency Inversion Principle
Q13. What is the difference between an interface and an abstract class?
Answer:
An interface defines a contract that implementing classes must follow, while an abstract class provides both common implementation and abstract methods.
| Interface | Abstract Class |
| Defines behavior only | Defines behavior and shared implementation |
| Supports multiple implementations | Supports single inheritance in most languages |
| No object creation | No object creation |
| Best for unrelated classes | Best for closely related classes |
Choose an interface when multiple classes need the same capability and an abstract class when classes share common functionality.
Q14. What is object cloning?
Answer:
Object cloning means making an exact copy of an existing object. The new object starts with the same values as the original but exists independently in memory. This is useful when you want to create similar objects quickly without repeating the same initialization code. Some languages support cloning through built-in methods or interfaces.
There are two types:
- Shallow Copy – Copies references to nested objects.
- Deep Copy – Creates completely independent copies of all nested objects.
Deep copying is preferred when changes to one object should not affect the copied object.
Q15. What is object serialization?
Answer:
Object serialization is the process of converting an object into a format that can be easily saved or transferred. For example, you can save an object’s data to a file or send it over a network. Later, you can restore the object using deserialization, which recreates it with the same data and values it had before.
Deserialization converts the byte stream back into an object.
Serialization is commonly used for caching, distributed systems, APIs, and data persistence.
Q16. What is loose coupling in OOP?
Answer:
Loose coupling in OOP means designing classes so that they have minimal dependency on each other. This allows one Class to be changed or replaced without affecting the rest of the application. As a result, the code becomes easier to test, maintain, and extend. Developers commonly achieve loose coupling by using interfaces, dependency injection, and design patterns that reduce direct dependencies between classes.
Q17. What are design patterns in OOP?
Answer:
Design patterns are reusable solutions to common software design problems that help developers write clean, flexible, and maintainable code.
Some popular OOP design patterns include:
- Singleton – Ensures only one instance of a class exists throughout the application.
- Factory – Creates objects without exposing the object creation logic.
- Builder – Constructs complex objects step by step.
- Observer – Notifies multiple objects automatically when one object’s state changes.
- Strategy – Allows different algorithms or behaviors to be selected at runtime.
- Adapter – Makes incompatible classes work together by acting as a bridge.
- Decorator – Adds new functionality to an object without modifying its original code.
Q18. What is dependency injection?
Answer:
Dependency Injection (DI) is a design technique where an object receives its required dependencies from an external source instead of creating them internally.
DI promotes loose coupling, simplifies testing, and makes applications easier to maintain.
Modern frameworks such as Spring, ASP.NET Core, and Angular extensively use dependency injection.
Q19. How is method overriding different from method overloading?
Answer:
Method overloading allows multiple methods with the same name but different parameter lists within the same Class. Method overriding allows a child class to provide its own implementation of a method already defined in its parent class. Overloading is resolved at compile time, while overriding is resolved at runtime.
Q20. Why is OOP widely used in modern software development?
Answer:
OOP helps developers build scalable, reusable, and maintainable applications by organizing code into classes and objects.
Its key advantages include:
- Better code organization: Classes and objects keep code structured and easy to understand.
- High reusability: Existing code can be reused, reducing development time.
- Easier maintenance: Changes can be made with minimal impact on other parts of the application.
- Improved scalability: Applications can grow by adding new features without major redesign.
- Enhanced security through encapsulation: Sensitive data is protected by restricting direct access.
- Simplified testing and debugging: Smaller, independent classes make it easier to find and fix issues.
- Better support for team-based development: Multiple developers can work on different classes simultaneously.
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