Most asked Oops Interview Questions

Most Asked Oops Interview Questions:-

1. What is Object-Oriented Programming (OOP)?

   - OOP is a programming paradigm that uses objects to model real-world entities. It involves encapsulation, inheritance, and polymorphism.

2. What is a class in OOP?

   - A class is a blueprint for creating objects. It defines the properties and behaviors that objects of the class will have.

3. What is an object in OOP?

   - An object is an instance of a class. It represents a real-world entity with specific attributes and behaviors.

4. Explain the four fundamental principles of OOP.

   - Encapsulation, Inheritance, Polymorphism, and Abstraction.

5. What is encapsulation?

   - Encapsulation is the concept of bundling data (attributes) and methods (functions) that operate on that data into a single unit, called a class.

6. What is inheritance?

   - Inheritance is the mechanism by which one class can inherit properties and methods from another class. It promotes code reusability.

7. What is polymorphism?

   - Polymorphism allows objects of different classes to be treated as objects of a common base class. It enables method overloading and method overriding.

8. What is abstraction?

   - Abstraction is the process of simplifying complex reality by modeling classes based on the essential characteristics of an object, hiding the irrelevant details.

9. What is a constructor?

   - A constructor is a special method in a class that is automatically called when an object of the class is created. It is used to initialize object attributes.

10. What is method overloading?

    - Method overloading is when a class has multiple methods with the same name but different parameters. The method called depends on the number or type of arguments passed.

11. What is method overriding?

    - Method overriding is when a subclass provides a specific implementation of a method that is already defined in its superclass.

12. What is a superclass and subclass?

    - A superclass (or parent class) is a class from which other classes (subclasses or child classes) inherit properties and methods.

13. What is the 'this' keyword in OOP?

    - 'this' refers to the current instance of a class and is often used to distinguish between instance variables and method parameters with the same name.

14. What is a static method?

    - A static method is a method that belongs to the class itself, rather than an instance of the class. It is called on the class, not on an object.

15. What is an abstract class?

    - An abstract class is a class that cannot be instantiated on its own and typically contains abstract methods that must be implemented by its subclasses.

16. What is an interface?

    - An interface is a contract specifying a set of methods that a class must implement. It defines what a class can do, without specifying how it does it.

17. What is multiple inheritance, and why is it not supported in some OOP languages?

    - Multiple inheritance is the ability of a class to inherit from more than one class. It can lead to ambiguity and complexity, which is why some languages don't support it.

18. What is a constructor chaining?

    - Constructor chaining is the process of calling one constructor from another within the same class to avoid redundant code.

19. What is a destructor?

    - A destructor is a special method that is called when an object is destroyed or goes out of scope. It is used for cleanup tasks.

20. What is the difference between composition and inheritance?

    - Composition is a "has-a" relationship where one class contains another class, while inheritance is an "is-a" relationship where one class derives from another.

21. What is a design pattern?

    - A design pattern is a reusable solution to a common problem in software design. It provides a template for structuring and solving specific design issues.

22. What is the Singleton design pattern?

    - The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance.

23. What is the Factory design pattern?

    - The Factory pattern is a creational pattern that provides an interface for creating objects but allows subclasses to alter the type of objects that will be created.

24. What is the Observer design pattern?

    - The Observer pattern is a behavioral pattern that defines a one-to-many dependency between objects. When one object changes state, all its dependents are notified.

25. What is method hiding in OOP?

    - Method hiding occurs when a subclass defines a static method with the same name as a static method in its superclass. It does not override the superclass method.

26. What is the difference between shallow copy and deep copy?

    - A shallow copy duplicates the object structure but not the objects themselves, while a deep copy duplicates the object structure as well as the objects it references.

27. What is the 'final' keyword in OOP?

    - The 'final' keyword is used to indicate that a class, method, or variable cannot be extended, overridden, or modified, depending on where it is used.

28. What is a package in Java?

    - A package is a way to organize related classes and interfaces into a namespace to prevent naming conflicts and make the code more modular.

29. What is the 'this' pointer in C++?

    - In C++, 'this' is a pointer that points to the current object. It is used to access the members of the current object within the class.

30. What is dynamic dispatch in the context of OOP?

    - Dynamic dispatch allows the runtime environment to determine which method to call based on the actual type of the object rather than the reference type.

31. What is a virtual function in C++?

    - A virtual function in C++ is a function declared in a base class with the 'virtual' keyword, which can be overridden by derived classes.

32. What is a garbage collector?

    - A garbage collector is a part of a programming language runtime system that automatically reclaims memory occupied by objects that are no longer in use.

33. What is method chaining (fluent interface)?

    - Method chaining is a design pattern that allows consecutive method calls on an object to be chained together, resulting in more readable and concise code.

34. What is the SOLID principles in OOP?

    - SOLID is an acronym for five principles: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion. These principles promote clean and maintainable code.

35. What is the DRY principle?

    - DRY stands for "Don't Repeat Yourself." It's a software development principle that encourages reusing code and avoiding duplicating logic.

36. What is a composition over inheritance?

    - Composition over inheritance is a design principle that recommends favoring object composition (using other objects) instead of relying on class inheritance to achieve code reuse.

37. What is the Law of Demeter?

    - The Law of Demeter (LoD) is a design guideline that suggests objects should only communicate with their immediate neighbors, reducing coupling between objects.

38. What is a UML diagram?

    - A UML (Unified Modeling Language) diagram is a graphical representation used to model software systems and their components, including classes, relationships, and behavior.

39. What is a mixin in O

OP?

    - A mixin is a class that provides a set of methods to be used by other classes, without being the parent of those classes. It's a form of code reuse.

40. What is the 'super' keyword in Java and Python?

    - The 'super' keyword is used to call a method or constructor from the parent class. It is often used in cases of method overriding.

41. What is a design pattern anti-pattern?

    - A design pattern anti-pattern is a common design approach that appears to be helpful but is ineffective or counterproductive when applied inappropriately.

42. What is the difference between an instance variable and a class variable?

    - An instance variable is specific to each object instance, while a class variable is shared among all instances of a class.

43. What is a circular reference in OOP?

    - A circular reference occurs when two or more objects reference each other, potentially causing memory leaks and making it challenging to manage object lifetimes.

44. What is a pure virtual function in C++?

    - A pure virtual function is a virtual function declared with "= 0" in the base class, indicating that it must be overridden in derived classes. It makes the class abstract.

45. What is a friend class in C++?

    - A friend class in C++ is a class that is allowed to access the private and protected members of another class. It's used for specialized scenarios where encapsulation needs to be relaxed.

46. What is method resolution order (MRO) in Python?

    - MRO is the algorithm used in Python to determine the order in which base classes are searched when a method is called on an object. It follows the C3 Linearization algorithm.

47. What is the role of the 'extends' keyword in Java and C#?

    - The 'extends' keyword in Java and the ':' symbol in C# are used to denote inheritance, indicating that a class is inheriting from another class.

48. What is composition root in dependency injection?

    - The composition root is the part of a software application that is responsible for creating and configuring the object graph for dependency injection.

49. What is the decorator pattern?

    - The decorator pattern is a structural pattern that allows behavior to be added to individual objects, either statically or dynamically, without affecting the behavior of other objects from the same class.

50. What is the Liskov Substitution Principle (LSP)?

    - The Liskov Substitution Principle states that objects of a derived class must be substitutable for objects of the base class without affecting the correctness of the program.