@Override
    public void putAll(Map<? extends K, ? extends Double> m) {
        int n = m.size();
        if (n == 0)
            return;
        if (n > threshold) // conservatively pre-expand
            resize(capacity(n));

        for (Entry<? extends K, ? extends Double> e : m.entrySet())
            put(e.getKey(), e.getValue());
    }