1) Immutable Class, date and List. Make thread safe. 2) Employee has list of addresses, how to store it. Comparable and Comparator difference 3) Auto boxing Unboxing 4) Can we use HashMap in a multi-threaded environment? a. We can use concurrent hashmap in a multi-threaded environment. b. Yes, Only if we create and use hashmap inside a method. c. Yes, We can use hashmap as instance variable and can perform read and write to it without any issue. d. Yes, We can use Hashmap if its declared as static. 5) write hashcode and equals method 6) What are blocking and non blocking APIs 7) What is circular dependency in Spring boot how to resolve it. 8) What is optimistic locking in hibernate 9) What is Deep and shadow cloning. 10) Difference in equals method and ==. 11) What are memory areas in Garbage collector. 12) When JVM calls GC? 13) What is Cookie and how it is used and sends over the server ? 14) How to use transactional while fetching data from DB. 15) One method is calling another method of service class and i want to make whole flow transaction as both methods update the data of db. How to achieve it and when does the commit happens. 16) What is String pool. 17) What is Web flux. 18) How to resolve DB error - 'Too many connections requests'