Round 2 :
Serialization, Object Cloning, Collections, Hibernate relationships, Spring AOP, Executer services, Concurrent hashmap (internal working), Reentrant Locks, Spring MVC, REST API, Synchronization, null related questions in collections, Singleton and factory design pattern.
Round 4 (Looking for specific answers):
Singleton design pattern, how singleton works in multithreaded environment, how java works with native OS thread, thread priority behaviour for singleton object in multithreading, resume explanations (questions will be on specific projects), what new technology explored other than mentioned in resume and questions on that, Green thread in java (outdated question), database optimized performance solution for fetching huge records. How to solve database related lazy loading performance issue.