/** Abridged from java.util.Map.
    Implemented by java.util.{Hash,Tree}Map.
*/
public interface Map<K,V>
{
   V put(K key, V value);           // return previous value if present
   boolean containsKey(Object key); // why Object?
   V get(Object key);
   boolean isEmpty();
   V remove(Object key);            // return previous value if present
   int size();
   Set<K> keySet();
}