How to sort a list of objects by an enum field?

Question

I have a list of objects that contains an enum field.

How can I sort it by the enum values alphabetically?

For example,

static enum Level { D, C, A, B } static class Item { Level level; public Item(Level level) { this.level = level; } } public static void main(String[] args) { Item item1 = new Item(Level.B); Item item2 = new Item(Level.A); Item item3 = new Item(Level.D); Item item4 = new Item(Level.C); List<Item> items = new ArrayList<>(List.of(item1, item2, item3, item4)); }

I want the order to be A,B,C,D

Why you don't use associative array instead of enum?

Lazar Đorđević
– Lazar Đorđević

2021-07-01 13:37:40 +00:00
Commented Jul 1, 2021 at 13:37 — Lazar Đorđević
– Lazar Đorđević, Commented Jul 1, 2021 at 13:37
Solution- stackoverflow.com/questions/1734872/…

Caffeine Coder
– Caffeine Coder

2021-07-01 14:07:35 +00:00
Commented Jul 1, 2021 at 14:07 — Caffeine Coder
– Caffeine Coder, Commented Jul 1, 2021 at 14:07

Sweeper · Accepted Answer · 2021-07-01 14:20:22Z

name returns the name of the enum constants, so you can use that in Comparator.comparing:

items.sort(Comparator.comparing(item -> item.level.name()));

After thinking about a bit further, I don't actually think this might not be a good design. If you do this, then you can't freely change your enum constant names, because that might also change the sort order. This is especially problematic if someone else who doesn't know that you are relying on enum names, reads your code and renames the constants for whatever reason (renaming normally won't break things if you use the IDE's rename tool), then your sorting code would sort them in a different order, which could potentially break many other things.

@Elimination After thinking about a bit further, I don't actually think this might not be a good design. If you do this, then you can't freely change your enum constant names, because that might also change the sort order, and that might be unwanted. This is especially problematic if someone else who doesn't know that you are relying on enum names, reads your code and renames the constants for whatever reason, then your sorting code would sort them in a different order, which could break other things.

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