HashMap
- It has pair values(keys,values)
- NO duplication key values
- unordered unsorted
- it allows one null key and more than one null values
HashTable
- same as hash map
- it does not allows null keys and null values
LinkedHashMap
- It is ordered version of map implementation
- Based on linked list and hashing data structures
TreeMap
- Ordered and sortered version
- based on hashing data structures