CheckedSortedMap(SortedMap<K, V> m,
    Class<K> keyType,
    Class<V> valueType) 
{
            super(m, keyType, valueType);
            sm = m;
}

 public Comparator<? super K> comparator() 
{
 return sm.comparator();
}

 public K firstKey() 
{
 return sm.firstKey();
}

 public SortedMap<K, V> headMap(K toKey) 
{
            return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
}

 public K lastKey() 
{
 return sm.lastKey();
}

 public SortedMap<K, V> subMap(K fromKey,
    K toKey) 
{
            return checkedSortedMap(sm.subMap(fromKey, toKey),
                                    keyType, valueType);
}

 public SortedMap<K, V> tailMap(K fromKey) 
{
            return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
}