The last question was just a map question.

You can reasonably assume that getTransaction returns null when
there is no input. Thus you repeatdely invoke getTransaction to
get a Transaction object and use it to update a map.




// Reads Transactions from scan (using getTransaction)
// and then combines Transactions into a Map that is
// created in computeSpending and then returned to the caller.
public Map<String,Integer> computeSpending( Scanner scan )
{
    Map<String,Integer> result = new HashMap<String,Integer>( );

    while( true )
    {
        Transaction t = getTransaction( scan );

        if( t == null )  // No more input
            return result;

        String person = t.getPerson( );
        Integer spent = result.get( person );

        if( spent != null )
            result.put( person, spent + t.getAmount( ) );
        else
            result.put( person, t.getAmount( ) );
    }
}