How should I search items in a nested HashMap with inner key?

Question

I have a nested HashMap HashMap<String, TreeMap<Integer, Item>>, and now I know the inner key Id(Integer) in TreeMap but don't have the key String in HashMap. Could I use some build-in methods or something else without iterating the HashMap to get what I want?

Previously, if I know the key String, I can use HashMap.get(String key)to get the item, and then use TreeMap.get(Integer inner_key), but I don't know what to do now if I don't have the outside key. Is it iterating the HashMap the only way?

Answer 1

"... Could I use some build-in methods or something else without iterating the HashMap to get what I want? ..."

Unfortunately not.  Although, an iteration is only a few lines.

String key(int i, HashMap<String, TreeMap<Integer, Item>> map) {
    for (Map.Entry<String, TreeMap<Integer, Item>> e : map.entrySet())
        if (e.getValue().containsKey(i)) return e.getKey();
    return null;
}

Alternately, use a stream.

String key(int i, HashMap<String, TreeMap<Integer, Item>> map) {
    return map.entrySet()
              .stream()
              .filter(x -> x.getValue().containsKey(i))
              .findFirst()
              .get().getKey();
}