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

Decorate map with your own implementation

class MyMap extends HashMap{

    Map reverseMap = new HashMap();

    @Override
    public V put(K key, V value) {
        // TODO Auto-generated method stub
        reverseMap.put(value, key);
        return super.put(key, value);
    }

    public K getKey(V value){
        return reverseMap.get(value);
    }
}