Why did a list with duplicates remain unsorted after removing duplicate elements?

If after removing duplicates the list remains unsorted, it is likely that the duplicate removal operation did not include sorting or an ordered container was not used. For example, when using HashSet to remove duplicates, the order of elements is not preserved because HashSet does not guarantee order. To preserve order and remove duplicates simultaneously, you can use LinkedHashSet, and then convert back to a list and sort if sorting is needed.

Example with order preservation and duplicate removal:

List<Integer> list = Arrays.asList(3, 1, 2, 3, 2);
LinkedHashSet<Integer> set = new LinkedHashSet<>(list); // removes duplicates, preserves order
List<Integer> uniqueList = new ArrayList<>(set);
Collections.sort(uniqueList); // sort the list

If sorting was not performed after duplicate removal, the list will remain in its original order without sorting.