Core Java Interview questions

CoreJavaInterviewQuestions.md

1. OOPs concepts Encapsulation, Abstraction, Inheritance, Polymorphism and explain
2. Exception hierarchy in inheritance
3. Parent child override scenario
4. Can we override static and private method?
5. Difference between Java 7 and Java 8 interface (static methods and default methods introduced)
6. Final, Finally, Finalize
7. Equals and hashcode
8. Why checked exception also called compile time exception, is it occurs in compile time?
9. How to write custom exception?
10. Throw and throws exception
11. Exception order
12. return usage in try, catch and finally block
13. Ss finally block always executed?
14. How many ways we can create string object?
15. String constant pool and working of it
16. Why string is immutable?
17. String vs StringBuffer vs StringBUilder
18. How to write your own custom immutable class?
19. Which is good to store passwords char array or string?
20. What is marker interface? (Serializable, Cloneable, Remote) and how and when it works?
21. Collections - List(ArrayList, LinkedList), Set(HashSet, LinkedHashSet, TreeSet), Map(HashMap, LinkedHashMap, TreeMap)
22. Concurrent - CopyOnWriteArrayList, CopyOnWriteArraySet, ConcurrentHashMap
23. List vs Set
24. ArrayList vs LinkedList
25. Custom array list without duplicates (extend array list and override add method)
26. ArrayList al = new ArrayList(); vs List l = new ArrayList<>();
27. Declaring list with final keyword
28. Why set does not allow duplicates?
29. Comparable vs Comparator
30. Fail fast vs fail safe iterator
31. HashMap vs ConcurrentHashMap
32. HashTable vs ConcurrentHashMap
33. Collections.synchronizedMap() - HashTable implementation - Entired data structure is locked
34. Internal working of HashMap - hash, bucket index, equals check, Linked List, Load factor, Balanced tree
35. Null key hashmap - 0th index bucket
36. TreeMap working