1. What are the ways to create object of class
  2. What are methods of Object class
  3. What is the difference between stack and heap memory
  4. What are the advantages and disadvantages of having 2 heap memory
  5. What is the difference between local and member/instance variable
  6. What is the difference between concrete method and abstract method and instance method
  7. What is static keyword? Where can we use static member
  8. What are major pillars of OOPS
  9. What is Encapsulation and Abstraction
  10. What is Polymorphism? How do we achieve polymorphism in Java?
  11. What is difference between declaration and initialization
  12. Abstract Class and Interface constructor
  13. Why only String class is final class and immutable not other classes
  14. What is serialization in Java
  15. What is boxing and unboxing
  16. What is upcasting and downcasting
  17. What is Marker interface
  18. What is functional interface
  19. What are the design pattern
  20. Design Pattern: Singleton, Factory, MVC
  21. What is REST API and SOAP
  22. What is difference between web API and Web Services
  23. What is Exception and its Hierarchy
  24. How to create exception class
  25. What is try catch finally throw throws
  26. Can we handle exception in finally block
  27. What is the difference between runtime and compile time exception
  28. How to handle out of memory exception
  29. What is Collection? What are different types of collections in Java
  30. What is legacy method and legacy classes
  31. Difference between HashMap and HashTree and HashTable
  32. How HashSet internally works
  33. What is Vector Class
  34. What is Comparable and Comparator
  35. Generics in Java
  36. Which collection is good for add and delete records
  37. Which collection is good for fast operations
  38. What is multithreading
  39. How to create thread without start and run method
  40. What is synchronized and volatile modifier