1. so let's say for a use case you need to pick up a list implementation and you have to pick between arraylist and link list which one you will pick and why 2. if we have to insert at the head or the tail then i would accept that okay that link list will be faster because you just have to switch the pointers but if you want to insert let’s say in the middle how many operations you would need in link list versus in array list for in the middle 3. in array list we have to shift the elements so you think the shifting of the elements will happen one by one like one element at it 4. can you explain to me how hashmaps work 5. and the worst case what will be the complexity 6. let’s say we have to use employee class object as a key in the map what we have to take care of 7. are the fields in the employee class mutable or should they be immutable 8. is the hashmap thread safe 9. what alternatives do we have we can use synchronized map we can use concurrent collections in which we have a concurrent hashmap as well 10. so synchronized map versus concurrent hashmap what was the difference 11. in a concurrent hashmap at a given point at the same time let’s say how many threads can do a put operation 12. what is the volatile keyword .