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☕ Java – Core Topics for Interviews

This section covers essential Java topics for technical interviews. Learn the Java Virtual Machine (JVM), object-oriented principles, interfaces, inheritance, method overriding, design patterns, collections, streams, and more. Each topic includes real code, MCQs, and interview Q&A for deeper understanding.

1. What is Java and its key features

2. Explain the Java Virtual Machine (JVM)

3. Difference between JDK, JRE, and JVM

4. What are Java’s main data types

5. Explain the concept of Object-Oriented Programming in Java

6. What is the difference between a class and an object

7. Explain encapsulation with an example

8. What is inheritance in Java and its types

9. Define polymorphism in Java with examples

10. What is abstraction in Java

11. Difference between abstract class and interface in Java

12. Explain method overloading and method overriding in Java

13. What are constructors in Java

14. What is the use of the static keyword in Java

15. Explain the difference between final, finally, and finalize in Java

16. What is a package and its benefits in Java

17. What are access modifiers in Java

18. Difference between checked and unchecked exceptions in Java

19. What is the try-catch-finally block in Java

20. Explain throw vs throws in Java

21. What is multi-threading in Java

22. How to create a thread in Java

23. Difference between Runnable and Thread class in Java

24. What is synchronization and why is it used in Java

25. Explain thread lifecycle in Java

26. What is inter-thread communication in Java

27. What are Java Collections Framework classes

28. Difference between ArrayList and LinkedList in Java

29. Explain HashMap vs Hashtable in Java

30. What is a Set in Java and its implementations

31. Difference between Iterator and ListIterator in Java

32. What is Java Stream API

33. Explain lambda expressions in Java

34. What is Functional Interface in Java

35. What is Java 8 Optional class

36. Explain the difference between Comparable and Comparator in Java

37. What is Garbage Collection in Java

38. How does JVM manage memory

39. What are the different types of memory areas in JVM

40. Explain the concept of classloader in Java

41. What is reflection and how is it used

42. Difference between

43. What is the purpose of the hashCode() method

44. Explain the concept of immutability

45. What is a String pool in Java

46. Difference between String, StringBuilder, and StringBuffer

47. What is serialization in Java

48. How to make a class serializable

49. What is transient keyword in Java

50. Explain enums in Java

51. What is a nested class and its types

52. Difference between static nested class and inner class

53. Explain anonymous classes

54. Explain try-with-resources statement

55. What is Java JDBC and how does it work

56. What are prepared statements in Java

57. Explain connection pooling in Java

58. What is ORM and Hibernate in Java

59. Difference between Array and ArrayList in Java

60. Explain autoboxing and unboxing in Java

61. What is type erasure in Java Generics

62. Explain wildcard types in Java Generics

63. Difference between List and Set in Java

64. What is the diamond operator in Java

65. Java Memory Model (JMM) Explained

66. What is volatile keyword in Java

67. What are Atomic Variables in Java

68. What is Deadlock and How to Avoid It in Java

69. Explain wait(), notify(), and notifyAll() in Java

70. What is a Thread Pool and How to Create It in Java

71. What is Callable and Future in Java Concurrency

72. Difference Between sleep() and wait() in Java

73. What is a Daemon Thread in Java

74. Explain the Singleton Design Pattern in Java

75. How to Implement a Thread-Safe Singleton in Java

76. What is Dependency Injection in Java

77. What are Annotations in Java

78. Explain the Lifecycle of a Servlet

1. What is Java and its key features

2. Explain the Java Virtual Machine (JVM)

3. Difference between JDK, JRE, and JVM

4. What are Java’s main data types

5. Explain the concept of Object-Oriented Programming in Java

6. What is the difference between a class and an object

7. Explain encapsulation with an example

8. What is inheritance in Java and its types

9. Define polymorphism in Java with examples

10. What is abstraction in Java

11. Difference between abstract class and interface in Java

12. Explain method overloading and method overriding in Java

13. What are constructors in Java

14. What is the use of the static keyword in Java

15. Explain the difference between final, finally, and finalize in Java

16. What is a package and its benefits in Java

17. What are access modifiers in Java

18. Difference between checked and unchecked exceptions in Java

19. What is the try-catch-finally block in Java

20. Explain throw vs throws in Java

21. What is multi-threading in Java

22. How to create a thread in Java

23. Difference between Runnable and Thread class in Java

24. What is synchronization and why is it used in Java

25. Explain thread lifecycle in Java

26. What is inter-thread communication in Java

27. What are Java Collections Framework classes

28. Difference between ArrayList and LinkedList in Java

29. Explain HashMap vs Hashtable in Java

30. What is a Set in Java and its implementations

31. Difference between Iterator and ListIterator in Java

32. What is Java Stream API

33. Explain lambda expressions in Java

34. What is Functional Interface in Java

35. What is Java 8 Optional class

36. Explain the difference between Comparable and Comparator in Java

37. What is Garbage Collection in Java

38. How does JVM manage memory

39. What are the different types of memory areas in JVM

40. Explain the concept of classloader in Java

41. What is reflection and how is it used

42. Difference between

43. What is the purpose of the hashCode() method

44. Explain the concept of immutability

45. What is a String pool in Java

46. Difference between String, StringBuilder, and StringBuffer

47. What is serialization in Java

48. How to make a class serializable

49. What is transient keyword in Java

50. Explain enums in Java

51. What is a nested class and its types

52. Difference between static nested class and inner class

53. Explain anonymous classes

54. Explain try-with-resources statement

55. What is Java JDBC and how does it work

56. What are prepared statements in Java

57. Explain connection pooling in Java

58. What is ORM and Hibernate in Java

59. Difference between Array and ArrayList in Java

60. Explain autoboxing and unboxing in Java

61. What is type erasure in Java Generics

62. Explain wildcard types in Java Generics

63. Difference between List and Set in Java

64. What is the diamond operator in Java

65. Java Memory Model (JMM) Explained

66. What is volatile keyword in Java

67. What are Atomic Variables in Java

68. What is Deadlock and How to Avoid It in Java

69. Explain wait(), notify(), and notifyAll() in Java

70. What is a Thread Pool and How to Create It in Java

71. What is Callable and Future in Java Concurrency

72. Difference Between sleep() and wait() in Java

73. What is a Daemon Thread in Java

74. Explain the Singleton Design Pattern in Java

75. How to Implement a Thread-Safe Singleton in Java

76. What is Dependency Injection in Java

77. What are Annotations in Java

78. Explain the Lifecycle of a Servlet

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