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HashSet vs TreeSet in Java

Answer»

The HashSet class implements the Set interface, supported by a Hashtable. Due to the implementation of the Set Interface, duplicate VALUES are not ALLOWED. The underlying data structure for a HashSet is a Hashtable.

The TREESET class implements the SortedSet interface, which in turn extends the Set interface. Objects are stored in a sorted ascending order. The underlying data structure for TreeSet is a tree.

Here are a few notable differences between a HashSet and a TreeSet:

Basis
HashSet
TreeSet
Performance
HashSet in Java offers faster performance than TreeSet
TreeSet in Java is slower than HashSet for most of the generic operations like add, remove and search.
Underlying data structure
HashSet has hashtable as its underlying data structure.
TreeSet has a red black tree as its underlying data structure.
NULL element
HashSet does allow one null element
TreeSet doesn’t allow any null element to be present
Implementation
It is implemented by HashMap
It is implemented by TreeMap
Interface
HashSet implements the Set interface.
TreeSet implements the SortedSet interface. SortedSet interface extends the Set interface.
Sorting
HashSet is not in sorted order
TreeSet is sorted in ascending order
COMPARISON
HashSet applies the equals() method for comparison
TreeSet applies the compareTo() method for comparison.


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