Collection interview question:

1. How TreeMap works in Java

       a) How to use Comparator and Comparable in Java

2. How HashMap works in Java

       a) How to override hashCode method

       b) How to override equals method 
             - Best practices to avoid NPE

3. How HashSet works in Java
4. Difference between HashMap and HashTable
5. Difference between List and Set in Java
6. What is Iterator and ListIterator
7. What is the difference between fail-fast and fail-safe Iterator
8. Different between synchronized collection and Concurrent collection
9. Difference between Iterator and Enumeration
10. How do you sort objects on collection
11. Difference between ArrayList and Vector (How ArrayList works)
12. Difference between HashSet and HashMap