1. what is java polymorphism - how java implements polymorphism? 2. purpose of volatile keyword 3. can top level class be declared static? 4. when is object.finalise method, when is it called? 5. Can we syncronise the static method 6. Can we invoke non static method from static method on same class 7. Producer and consumer pattern explain?? 8. Which design pattern u used in ur projects? 9. Describe heirarchy of exception class 10. Java collection api - describe a few? 11. Describe transient variable 12. Describe final keyword 13. Multithreading - how to create multiple thread, describe how to start new thread 14. Difference between runnable and callable 15. Difference between treemap and hashmap? 16. String, string builder and string buffer differences 17. Java io apis which u used -? 18. Singleton pattern - explain 19. How do you make class singleton.