Java Hashmap: How to get key from value?

Question

If I have the value \"foo\", and a HashMap ftw for which ftw.containsValue(\"foo\") returns true, how can I

Answer 1

I think keySet() may be well to find the keys mapping to the value, and have a better coding style than entrySet().

Ex:

Suppose you have a HashMap map, ArrayList res, a value you want to find all the key mapping to , then store keys to the res.

You can write code below:

    for (int key : map.keySet()) {
        if (map.get(key) == value) {
            res.add(key);
        }
    }

rather than use entrySet() below:

    for (Map.Entry s : map.entrySet()) {
        if ((int)s.getValue() == value) {
            res.add((int)s.getKey());
        }
    }

Hope it helps :)