/**
     * Ensures capacity when the size exceeds the threshold.
     */
    protected void ensureCapacity() {
        if (size >= threshold) {
            final Entry<K, V>[] oldTable = listTable;
            final int newCapacity = oldTable.length * 2 + 1;
            @SuppressWarnings("unchecked")
            final Entry<K, V>[] newMapTable = new Entry[newCapacity];
            @SuppressWarnings("unchecked")