| Property | HashSet | LinkedHashSet | TreeSet |
|---|---|---|---|
| Underline Data Structure | HashTable | HashTable + LinkedList | BalancedTree |
| Duplicacy | Not Allowed | Not Allowed | Not Allowed |
| Insertion Order | Not Preserved | Preserved | Not Preserved |
| Sorting Order | Not Applicable | Not Applicable | Applicable |
| Heterogeneous Object | Allowed | Allowed | Not Allowed |
| Null Insertion | Allowed | Allowed | Not Allowed |
Note- In TreeSet null insertion is allowed as the first element until Java 1.6v, but after 1.7v null insertion is not allowed.