[onlycoffee]

Depends on the use case, sometimes a list is more appropriate. On an old machine, Java 17 can iterate a list of 30 million strings looking for a match in around a half second. Just checked it in jshell. If the use case was that the map's keys could potentially change over the lifetime of the map or if the value's were not idempotent and if iterating 30 million items occurs fairly infrequently, then an ArrayList (in Java) might be the best choice.