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📘 Top 50 Interview Questions – Object-Oriented Programming (OOP) #9
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📘 Top 50 Interview Questions – Object-Oriented Programming (OOP)
This repository contains Top 50 frequently asked interview questions covering Object-Oriented Programming (OOP) and core Java concepts.
It is designed for freshers, students, and experienced developers preparing for technical interviews.
📌 Table of Contents
🧱 Object-Oriented Programming (OOP)
1. What is OOP?
Answer:
OOP (Object-Oriented Programming) is a programming paradigm based on objects and classes to structure software in a reusable, scalable, and maintainable way.
2. What are the four main principles of OOP?
Answer:
3. What is encapsulation?
Answer:
Encapsulation is the process of bundling data (variables) and methods that operate on that data into a single unit (class) and restricting direct access.
4. What is inheritance?
Answer:
Inheritance allows a class to acquire properties and behaviors of another class, promoting code reusability.
5. What is polymorphism?
Answer:
Polymorphism allows a method to behave differently based on the object that invokes it.
6. What is abstraction?
Answer:
Abstraction hides implementation details and exposes only essential features.
7. Difference between class and object?
Answer:
8. What is a constructor?
Answer:
A constructor is a special method used to initialize objects of a class.
9. What is method overloading?
Answer:
Defining multiple methods with the same name but different parameter lists.
10. What is method overriding?
Answer:
Providing a new implementation of a parent class method in a subclass.
11. What is an exception?
Answer:
An exception is an event that disrupts the normal flow of program execution.
12. Difference between checked and unchecked exceptions?
Answer:
13. What is try-catch?
Answer:
Used to handle exceptions and prevent program termination.
14. Purpose of finally block?
Answer:
Executes code regardless of whether an exception occurs.
15. What is
throwkeyword?Answer:
Used to explicitly throw an exception.
16. What is
throwskeyword?Answer:
Used to declare exceptions that a method may pass to the caller.
17. Difference between throw and throws?
Answer:
throw: Throws an exceptionthrows: Declares possible exceptions18. What is a custom exception?
Answer:
A user-defined exception created by extending
ExceptionorRuntimeException.19. What is try-with-resources?
Answer:
Automatically closes resources after execution.
20. What are runtime exceptions?
Answer:
Exceptions that occur during program execution due to logical errors.
🔤 Strings
21. What is a String in Java?
Answer:
An immutable object representing a sequence of characters.
22. Difference between String, StringBuilder, StringBuffer?
Answer:
23. How to compare strings?
Answer:
Using the
equals()method.24. What is intern()?
Answer:
Returns a canonical representation of a string from the string pool.
25. What is string concatenation?
Answer:
Combining strings using
+orconcat().26. Convert string to integer?
Answer:
Integer.parseInt()27. What is substring()?
Answer:
Extracts a portion of a string using index values.
28. What is String.format()?
Answer:
Used to create formatted strings.
29. How to check if a string contains text?
Answer:
Use the
contains()method.30. What is StringBuilder used for?
Answer:
Efficient manipulation of mutable strings.
🧵 Multithreading
31. What is a thread?
Answer:
A lightweight process that executes tasks independently.
32. Runnable vs Thread?
Answer:
33. How to create a thread?
Answer:
ThreadclassRunnableinterface34. What is synchronized?
Answer:
Ensures only one thread accesses a shared resource at a time.
35. What is deadlock?
Answer:
A situation where threads wait indefinitely for resources.
36. What is thread safety?
Answer:
Code behaves correctly when accessed by multiple threads.
37. What is join()?
Answer:
Waits for a thread to complete execution.
38. What is volatile?
Answer:
Ensures visibility of variable changes across threads.
39. Thread states?
Answer:
New, Runnable, Blocked, Waiting, Timed Waiting, Terminated.
40. What is a thread pool?
Answer:
A group of reusable threads for executing tasks efficiently.
📦 Collections
41. What is Java Collections Framework?
Answer:
A unified architecture for storing and manipulating collections.
42. List vs Set vs Map?
Answer:
43. What is ArrayList?
Answer:
Resizable array implementation of List.
44. What is HashSet?
Answer:
Unordered collection with no duplicates.
45. What is LinkedList?
Answer:
Doubly-linked list implementation.
46. What is HashMap?
Answer:
Stores key-value pairs using hashing.
47. HashMap vs TreeMap?
Answer:
48. What is PriorityQueue?
Answer:
Queue ordered by priority.
49. What is LinkedHashMap?
Answer:
Maintains insertion order.
50. How to iterate over collections?
Answer:
Using Iterator or enhanced for-loop.
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