How does TreeSet in Java ensure the uniqueness of elements and on what basis does it determine that elements are the same?

TreeSet in Java ensures the uniqueness of elements by using a data structure based on a balanced tree (usually a red-black tree), where elements are stored in sorted order.

Uniqueness is determined not through the equals() method, but through comparison of elements using the compareTo() method of the Comparable interface or a Comparator passed to the TreeSet constructor.

If compareTo() returns 0 for two elements, TreeSet considers them the same and does not add a duplicate.

Example:

TreeSet<String> set = new TreeSet<>();
set.add("apple");
set.add("banana");
set.add("apple"); // will not be added, as compareTo will return 0

Therefore, for the correct operation of TreeSet, it is important that the comparison is consistent with the logic of element uniqueness.