I suggest a LinkedHashMap
or a TreeMap
. A LinkedHashMap
keeps the keys in the order they were inserted, while a TreeMap
is kept sorted via a Comparator
or the natural Comparable
ordering of the elements.
Since it doesn’t have to keep the elements sorted, LinkedHashMap
should be faster for most cases; TreeMap
has O(log n)
performance for containsKey
, get
, put
, and remove
, according to the Javadocs, while LinkedHashMap
is O(1)
for each.
If your API that only expects a predictable sort order, as opposed to a specific sort order, consider using the interfaces these two classes implement, NavigableMap
or SortedMap
. This will allow you not to leak specific implementations into your API and switch to either of those specific classes or a completely different implementation at will afterwards.