In-order access to LinkedHashMap keys

[dmolesUC]

Presumably for reasons of efficiency, LinkedHashMap.keySet() returns the unordered keySet of the underlying HashMap. It would be convenient to be able to get the keys in order without having to resort to a workaround like map.iterator().map(entry -> entry._1), even if the underlying implementation isn't any less ugly than that. E.g.

/** Returns the keys contained in this map, in insertion order. */
public Queue<K> keys() {
  return list.map(entry -> entry._1);
}

(Forgive me if there's a more idiomatic way to do this; I have some Scala background but I've been stuck in Ruby for a year or two, and my Java and Javaslang are both rusty.)

[ruslansennov]

We can't change LinkedHashMap::keys signature as you proposed, because it will clash with method in super interface. However we could change it to something like this

    @Override
    public Set<K> keySet() {
        return new LinkedHashSet(this);
    }

This would keep order of elements

[dmolesUC]

That's why I suggested adding keys() rather than changing keySet(), but the LinkedHashSet idea is much, much better — I forgot that a LinkedHashSet is backed by a LinkedHashMap.

To do that, though, wouldn't you also need to change the LinkedHashSet constructor to take a LinkedHashMap<T, Object> rather than a LinkedHashMap<T, T>?

[ruslansennov]

That's why I suggested adding keys() rather than changing keySet()

Oh, sorry :)

To do that, though, wouldn't you also need to change the LinkedHashSet constructor to take a LinkedHashMap<T, Object> rather than a LinkedHashMap<T, T>?

Yes, wrapped map should be changed to

private final LinkedHashMap<T, Object> map;

[ruslansennov]

java.util.LinkedHashMap.keySet() also keeps order

[danieldietrich]

Fixed with #1854