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Core Java Interview Questions

  1. How does serialization takes place in Java ? What is purpose of externalizable interface ? What are transient variables ?
  2. Why most of methods in Collections class declared as static ?
  3. What is difference between overloading and overriding ? What is hiding of members and methods - both static and instance one ?
  4. What is ThreadLocal class used for ?
  5. What is purpose of Classloader provided by Java ? What is effect of multiple classloaders on Singleton Class ?
  6. NoClassDefFoundError vs ClassNotFoundException ?
  7. What kind of exceptions we have in Java?
  8. What is run time and unchecked exceptions?
  9. How we can achieve exception free code?
  10. What we need to use among these Exception vs RuntimeException when we are creating custom exceptions?
  11. What we have to do when exception raise and when it will rise in case of checked?
  12. Hash set internal implementation?
  13. Array list how it works internally?
  14. How hash set works and what is the difference between hash map and hash set?
  15. Array list vs linked list?
  16. Comparable vs comparator and what you will prefer ?
  17. Hash code collision?
  18. Hash map internal working.
  19. Tree set internal working.
  20. Comparator property sorting example?
  21. Why List allows sorting if the type is String?
  22. Linkedlist internal implementation?
  23. Priority queue and implement sample?
  24. failfast vs failsafe
  25. Stack implementation using arrays
  26. Hash map vs Concurrent Hash map
  27. Hash map internal implementation when we insert null as key?
  28. Explain Iterator vs Enumerator vs List Iterator
  29. Why we need object as key in hash map
  30. Abstract list vs abstract map vs abstract set
  31. What is the heirarchy or LinkedList?
  32. How we can avoid race condition of Class and Object variables.
  33. How exactly class level and object level locks works?
  34. What if 2 different objects of threads operating on same shared object?
  35. What is cyclic barrier how it works?
  36. What is starvation?
  37. How we can resolve starvation?
  38. Thread vs runnable which is preferable in terms of memory utilization?
  39. What is serialization where it is used?
  40. Difference between transient and volatile variable in Java
  41. Difference between Serializable and Externalizable interface in Java
  42. What if I changed my serial id while deserializing.
  43. Why character array is better than String for Storing password in Java
  44. How substring works?
  45. What is immutability?
  46. Why we need string as immutable?

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