The difference between HashSet and TreeSet in Java primarily revolves around their underlying data structures, performance characteristics, and ordering of elements.
Data Structure and Implementation
HashSet: It is implemented using a hash table. Elements are placed in the hash table based on the hash code of the elements. As a result, it does not maintain any order among the elements[1][2][4][5].
TreeSet: This is implemented using a Red-Black tree, a self-balancing binary search tree. Elements in a TreeSet are sorted according to their natural ordering, or by a Comparator provided at set creation time[1][2][4][5].
Performance
HashSet offers constant time performance for basic operations such as add, remove, and contains, assuming the hash function disperses the elements properly among the buckets[1][2][5].
TreeSet provides guaranteed log(n) time cost for the basic operations (add, remove and contains), which is generally slower than the constant time performance of HashSet. This is due to the overhead of maintaining order of elements[1][2][5].
Ordering of Elements
HashSet does not guarantee any specific order of its elements, as the order depends on the hash function[1][2][4][5].
TreeSet guarantees that the elements are sorted in ascending order, unless specified otherwise with a custom Comparator[1][2][4][5].
Null Elements
HashSet allows the inclusion of a null element, but on...
