public Object remove( Object key ) {
  if( key == null ) {
    throw new NullPointerException( "Key cannot be null." );
  }
  int index = _findKey( key );
  if( index == -1 ) {
    return null;	
  }
  Object oldValue = _table[index].getValue();
  _table[index] = AVAILABLE;
  return oldValue;
}