public class BiMap<K, V> implements Map<K, V> {
    private Map<K, V> values = Maps.newHashMap();
    private Map<V, K> keys = Maps.newHashMap();

    public void put(K k, V v) {
        values.put(k, v);
        keys.put(v, k);
    }

    public V get(K k) {
        return keys.get(k);
    }

    public K getKey(V v) {
        return values.get(v);
    }

    /* Everything else */
}