Difference between the hash map, hash table and hash set

Hash table

It didn’t allow null for both key and value. You will get NullPointerException if you add null value.

It is synchronized. So it comes with its cost. Only one thread can access in one time

Hash map

It allows null for both key and value

It is unsynchronized. So come up with better performance

Hash set

HashSet does not allow duplicate values. It provides add method rather put method. You also use its contain method to check whether the object is already available in HashSet. HashSet can be used where you want to maintain a unique list.