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 are the design pattern
  19. Design Pattern: Singleton, Factory, MVC
  20. What is REST API and SOAP
  21. What is difference between web API and Web Services
  22. What is Exception and its Hierarchy
  23. How to create exception class
  24. What is try catch finally throw throws
  25. Can we handle exception in finally block
  26. What is the difference between runtime and compile time exception
  27. How to handle out of memory exception
  28. What is Collection? What are different types of collections in Java
  29. What is legacy method and legacy classes
  30. Difference between HashMap and HashTree and HashTable
  31. How HashSet internally works
  32. What is Vector Class
  33. What is Comparable and Comparator
  34. Generics in Java
  35. Which collection is good for add and delete records
  36. Which collection is good for fast operations
  37. What is multithreading
  38. How to create thread without start and run method
  39. What is synchronized and volatile modifier