2026

OOP Interview Questions 2026

A current, 2026 snapshot of the OOP interview questions worth knowing — kept up to date as frameworks and best practices evolve, so you prepare with what companies are actually asking in 2026.

92Questions14Beginner14Intermediate64Senior

92 OOP questions

  1. 1What is polymorphic behavior in real systems?Intermediate
  2. 2What are design patterns in OOP?Intermediate
  3. 3What is aggregation vs composition in OOP?Intermediate
  4. 4What is Dependency Injection in OOP?Intermediate
  5. 5What is the Dependency Inversion Principle (DIP)?Intermediate
  6. 6What is the Interface Segregation Principle (ISP)?Intermediate
  7. 7What is the Open/Closed Principle (OCP)?Intermediate
  8. 8What is the Liskov Substitution Principle (LSP)?Intermediate
  9. 9What is the Single Responsibility Principle?Intermediate
  10. 10What are SOLID principles?Intermediate
  11. 11What is composition vs inheritance?Intermediate
  12. 12What are access modifiers in OOP?Beginner
  13. 13What is an interface in OOP?Beginner
  14. 14What is method overriding?Beginner
  15. 15What is method overloading?Beginner
  16. 16What is a constructor in OOP?Beginner
  17. 17What is abstraction in OOP?Beginner
  18. 18What is polymorphism in OOP?Beginner
  19. 19What is inheritance in OOP?Beginner
  20. 20What is encapsulation in OOP?Beginner
  21. 21What is a class and an object in OOP?Beginner
  22. 22OOP Interview Question 5 (Free)Intermediate
  23. 23OOP Interview Question 4 (Free)Beginner
  24. 24OOP Interview Question 3 (Free)Senior
  25. 25OOP Interview Question 2 (Free)Intermediate
  26. 26OOP Interview Question 1 (Free)Beginner
  27. 27What is coupling due to inheritance hierarchy depth?Senior
  28. 28What is runtime type identification (RTTI)?Senior
  29. 29What is interface-driven development?Senior
  30. 30What is immutability tradeoff in performance systems?Senior
  31. 31What is the difference between stateful and stateless objects?Senior
  32. 32What is encapsulation boundary leakage?Senior
  33. 33What is coupling in microservices vs monolithic OOP systems?Senior
  34. 34What is late binding and early binding in OOP?Senior
  35. 35What is object identity vs object equality?Senior
  36. 36What is the role of abstraction in system design scalability?Senior
  37. 37What is SOLID principle violation impact in large-scale systems?Senior
  38. 38What is the difference between runtime and compile-time polymorphism in real systems?Senior
  39. 39What is clean architecture in OOP systems?Senior
  40. 40What is hexagonal architecture in OOP?Senior
  41. 41What is a repository pattern in OOP?Senior
  42. 42What is a service layer in OOP architecture?Senior
  43. 43What is reflection abuse in OOP systems?Senior
  44. 44What is class loading in OOP runtime systems?Senior
  45. 45What is memory management in OOP runtime environments?Senior
  46. 46What is inversion of control (IoC) in OOP?Senior
  47. 47What is the difference between aggregation and composition in memory lifecycle terms?Senior
  48. 48What is object pooling and why is it used?Senior
  49. 49What is the role of virtual tables (vtable) in OOP?Senior
  50. 50What is the difference between interface and abstract class in depth?Senior
  51. 51What is performance optimization in OOP systems?Senior
  52. 52What is prototype-based OOP?Senior
  53. 53What is composition root in OOP architecture?Senior
  54. 54What is aspect-oriented programming (AOP)?Senior
  55. 55What is dependency injection container?Senior
  56. 56What is a deadlock in OOP systems?Senior
  57. 57What is synchronization in object-oriented programming?Senior
  58. 58What is concurrency in OOP systems?Senior
  59. 59What is event sourcing in OOP systems?Senior
  60. 60What is CQRS in object-oriented architecture?Senior
  61. 61What is a decorator pattern in OOP?Senior
  62. 62What is a proxy pattern in OOP?Senior
  63. 63What is deep cloning vs shallow cloning in OOP?Senior
  64. 64What is immutability in OOP and why is it important?Senior
  65. 65What is coupling in distributed OOP systems?Senior
  66. 66What is metaprogramming in OOP?Senior
  67. 67What is reflection in OOP?Senior
  68. 68What is event-driven architecture in OOP?Senior
  69. 69What is domain-driven design in OOP?Senior
  70. 70What is a memory leak in OOP systems?Senior
  71. 71What is garbage collection in OOP languages?Senior
  72. 72What is a virtual function?Senior
  73. 73What is cohesion vs coupling tradeoff?Senior
  74. 74What is the Diamond Problem in OOP?Senior
  75. 75What is multiple inheritance and its issues?Senior
  76. 76What is object slicing?Senior
  77. 77What is runtime polymorphism internally?Senior
  78. 78What is method binding in OOP?Senior
  79. 79What is the Observer Pattern?Senior
  80. 80What is the Strategy Pattern?Senior
  81. 81What is the Builder Pattern?Senior
  82. 82What is the Singleton Pattern?Senior
  83. 83What is the Factory Design Pattern?Senior
  84. 84What is cohesion in OOP design?Senior
  85. 85What is tight coupling vs loose coupling?Senior
  86. 86What is object lifecycle management in OOP?Senior
  87. 87How does OOP support scalable system architecture?Senior
  88. 88OOP Advanced Interview Question 9Senior
  89. 89OOP Advanced Interview Question 8Intermediate
  90. 90OOP Advanced Interview Question 7Beginner
  91. 91OOP Advanced Interview Question 6Senior
  92. 92OOP Advanced Interview Question 10Beginner

Explore more OOP interview questions

By Level

By Experience

Or browse all OOP interview questions.

Frequently asked questions

Are these OOP interview questions up to date for 2026?

Yes. This page reflects 92 OOP interview questions kept current with today's frameworks, tooling and interview trends, with each answer maintained and dated.

What OOP topics should I focus on in 2026?

Prioritise the fundamentals plus the modern patterns interviewers ask about now. Each question here includes a detailed answer, code example and common mistakes so you can target the highest-impact areas.

Are these questions free?

You can read the question and a short answer for free. A subscription unlocks the full detailed explanation, real-world example, common mistakes and follow-up questions for each one.