1.
    private void clearDataField( )
    {
        Set s = actorsToMovies.keySet( );
        Iterator itr = s.iterator( );

        while( itr.hasNext( ) )
            ( (Actor)itr.next( ) ).data = 0;
    }

2.
    public Set inSameMovies( Actor x )
    {
        Set result = new TreeSet( );

        Iterator itr1 = ( (List) actorsToMovies.get( x ) ).iterator( );
        while( itr1.hasNext( ) ) 
        {
            List otherActors = (List) moviesToActors.get( itr1.next( ) );

            Iterator itr2 = otherActors.iterator( );
            while( itr2.hasNext( ) )
                result.add( itr2.next( ) );
        }

        result.remove( x );   // x doesn't count

        return result;
    }