0| HashSet | HashMap |
| HashSet implements Set interface. | HashMap implements Map interface. |
| HashSet stores the data as objects. | HashMap stores the data as key-value pairs. |
| HashSet internally uses HashMap. | HashMap internally uses an array of Entry<K, V>objects. |
| HashSet doesn’t allow duplicate elements. | HashMap doesn’t allow duplicate keys, but allows duplicate values. |
| HashSet allows only one null element. | HashMap allows one null key and multiple null values. |
| Insertion operation requires only one object. | Insertion operation requires two objects, key and value. |
| HashSet is slightly slower than HashMap. | HashMap is slightly faster than HashSet. |
Similarities Between HashMap And HashSet In Java :
1) Both data structures don’t maintain any order for the elements.
2) Both use hashCode() and equals() method to maintain the uniqueness of the data.
3) The iterators returned by both are fail-fast in nature.
4) Both give constant time performance for insertion and removal operations.
5) Both are not synchronized.
