What is the Stream API in Java and what are its benefits?

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Java Interview Questions

  1. [JUNIOR] What is Java and what are its main features?
  2. [JUNIOR] What are the main principles of object-oriented programming in Java?
  3. [MID] What is the difference between ArrayList and LinkedList?
  4. [MID] What is the difference between HashMap and HashTable?
  5. [JUNIOR] What are the differences between JDK, JRE, and JVM?
  6. [JUNIOR] Why is Java a platform-independent language?
  7. [JUNIOR] What is the difference between == operator and equals() method in Java?
  8. [JUNIOR] What is inheritance in Java?
  9. [JUNIOR] What is polymorphism in Java?
  10. [MID] What is the difference between String, StringBuilder, and StringBuffer?
  11. [MID] What is the difference between Heap and Stack memory in Java?
  12. [MID] What are the different ways to create threads in Java?
  13. [MID] What is the synchronized keyword and why is it used?
  14. [SENIOR] How does garbage collection work in Java?
  15. [JUNIOR] What is the static keyword used for in Java?
  16. [JUNIOR] What is the difference between method overloading and method overriding?
  17. [JUNIOR] What is exception handling in Java?
  18. [JUNIOR] What is the difference between checked and unchecked exceptions?
  19. [JUNIOR] What is an interface in Java?
  20. [JUNIOR] What is the difference between abstract classes and interfaces?
  21. [JUNIOR] What is a constructor in Java and what is constructor overloading?
  22. [MID] Why are strings immutable in Java?
  23. [MID] What is the Java thread lifecycle and what are the different thread states?
  24. [MID] What is deadlock in Java and how can you prevent it?
  25. [MID] What is the volatile keyword in Java?
  26. [MID] What is the Stream API in Java and what are its benefits?
  27. [SENIOR] What are the different types of garbage collectors available in the JVM?
  28. [SENIOR] Why is composition preferred over inheritance?
  29. [SENIOR] What is a memory leak in Java and what are common causes of it?
  30. [SENIOR] How do you ensure immutability in a Java class and why is it important?
  31. [JUNIOR] What do you mean by data encapsulation in Java?
  32. [JUNIOR] What is the use of the final keyword in variable, method, and class?
  33. [JUNIOR] What is the difference between final, finally, and finalize?
  34. [JUNIOR] What is the difference between throw and throws keywords in Java?
  35. [JUNIOR] What is a try-catch block and how does the finally block work?
  36. [JUNIOR] Why is the main method static in Java?
  37. [MID] What makes a HashSet different from a TreeSet?
  38. [MID] What is a singleton class and how do you implement it in Java?
  39. [MID] What is the importance of reflection in Java?
  40. [MID] What is a Comparator and how does it differ from Comparable in Java?
  41. [MID] How does Java implement pass-by-value for objects?
  42. [MID] What are generics in Java and why are they used?
  43. [MID] What is the difference between map and flatMap in Streams?
  44. [SENIOR] What is the difference between CompletableFuture and Future?
  45. [SENIOR] What is the difference between ReentrantLock and synchronized?
  46. [SENIOR] What are the different categories of Java design patterns?
  47. [SENIOR] What is the best way to inject dependency in Java and why?
  48. [SENIOR] What are strong, weak, soft, and phantom references in Java?
  49. [EXPERT] What is the Java Memory Model and how does it affect concurrent programming?
  50. [JUNIOR] What are the default values assigned to variables and instances in Java?
  51. [JUNIOR] What do you understand by an instance variable and a local variable?
  52. [JUNIOR] What are wrapper classes in Java?
  53. [JUNIOR] What is autoboxing and unboxing in Java?
  54. [MID] What is thread safety and how do you achieve it in Java?
  55. [MID] How does the size of ArrayList grow dynamically?
  56. [MID] What is the difference between Iterator and ListIterator?
  57. [MID] What is the difference between a process and a thread?
  58. [MID] What is a marker interface in Java?
  59. [MID] What is Object Cloning and how do you achieve it in Java?
  60. [MID] What is the difference between shallow copy and deep copy in Java?
  61. [SENIOR] What is the difference between Composition and Aggregation?
  62. [SENIOR] How is the creation of a String using new() different from that of a literal?
  63. [SENIOR] What are the possible ways of making an object eligible for garbage collection?
  64. [SENIOR] How do you design a REST API in Spring Boot?
  65. [SENIOR] What causes N+1 queries in Hibernate and how do you fix them?
  66. [EXPERT] How does the JIT compiler optimize code execution at runtime?
  67. [EXPERT] How does HashMap internally handle hash collisions and rehashing?
  68. [EXPERT] How does the class loading mechanism work in Java, including parent delegation?
  69. [JUNIOR] What is a package in Java?
  70. [JUNIOR] What is a ClassLoader in Java?
  71. [JUNIOR] How is Java different from C++?
  72. [MID] Why is the character array preferred over String for storing confidential information?
  73. [MID] How do you prevent serialization of specific attributes of a class in Java?
  74. [MID] What is JDBC and what are its core components?
  75. [MID] What is the difference between Statement and PreparedStatement in JDBC?
  76. [MID] What is Connection Pooling and why is it important?
  77. [SENIOR] How do you handle database transactions safely in a Java backend?
  78. [SENIOR] Is it possible to exceed the memory limit despite having a garbage collector?
  79. [SENIOR] What are microservices and what are the challenges of building them with Java?
  80. [SENIOR] How do you improve API latency without just adding servers?
  81. [EXPERT] What is ConcurrentHashMap and how does it differ from a synchronized HashMap internally?
  82. [EXPERT] How do virtual threads in Project Loom differ from platform threads?
  83. [EXPERT] What happens when you call return in both a try block and a finally block?
  84. [JUNIOR] Why is Java not a pure object-oriented language?
  85. [MID] What is double brace initialization in Java?
  86. [MID] How does an exception propagate in the code?
  87. [SENIOR] How do you version APIs without breaking existing clients?
  88. [SENIOR] How would you optimize a large Java application's bundle size and startup time?
  89. [EXPERT] What are sealed classes and when would you use them?
  90. [EXPERT] How does the fork/join framework work and when should you use it?
  91. [JUNIOR] Can the main method be overloaded in Java?
  92. [MID] Why does the java array index start with 0?
  93. [SENIOR] How do you approach debugging a production issue end to end in a Java application?
  94. [EXPERT] Why does System.out.println('a' + 'b' + 'c') print a number instead of a string?
  95. [EXPERT] How does the JVM handle escape analysis and what optimizations does it enable?
  96. [EXPERT] What are the trade-offs between G1, ZGC, and Shenandoah garbage collectors?
  97. [EXPERT] How does the invokedynamic bytecode instruction work and why was it introduced?
  98. [EXPERT] What are the implications of false sharing in Java concurrent programs and how do you mitigate it?