How to sort a list without mutating it

Question

I would like to sort a List of items in Java and have the sort return a new sorted List without mutating the original List. Is there a commonly used library that does this?

All Java SE collection classes have a constructor that copies another collection. Using that, you can do `List sortedList = new ArrayList<>(unsortedList); sortedList.sort(null);` — VGR, Aug 24 '18 at 21:10
1) Copy it, sort the copy, or 2) `stream()` it, sort the `Stream`. Perhaps 3) create a sorted _view_ - but that would have `O(lg n)` access times, so probably not useful. — Boris the Spider, Aug 24 '18 at 21:10

score 8 · Accepted Answer · edited Aug 25 '18 at 10:14

8

If you are using Java 8 or higher, you can use the Stream API. See Sorting a list with stream.sorted() in Java for details.

For example:

List<String> sortedList = myList.stream().sorted().collect(Collectors.toList());

edited Aug 25 '18 at 10:14

Alex Spurling

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answered Aug 24 '18 at 21:06

Code-Apprentice

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score 2 · Answer 2 · edited Feb 14 '21 at 07:08

This copies (by reference) the elements in the original list to the new list. Making changes like the ordering of one list won't affect the other.

List<String> originalList = new ArrayList<String>();
List<String> newList = new ArrayList(originalList);

Please note if you modify the objects that are in the list however, the changes will be reflected in both lists since objects are copied by reference.

How to sort a list without mutating it

2 Answers2