public void upgrade()
   {
      if(canUpgrade)
      {
         ArrayList<Object> deedNames = new ArrayList<Object>();
         for (int i = 0; i < deeds.size(); i++)
         {
            Property prop = deeds.get(i);
            if (prop instanceof Street) deedNames.add(prop.name);
         }

         String[] names = deedNames.toArray(new String[deedNames.size()]); 

         String s = (String)JOptionPane.showInputDialog(null, 
                                    "Which property do you want to upgrade?",
                                    "Property Upgrade",
                                    JOptionPane.QUESTION_MESSAGE,
                                    null, 
                                    names,
                                    names[0]
                                 );
         if (s != null) 
         {
            int result = Arrays.asList(names).indexOf(s);       
            Street choice = (Street)deeds.get(result);
            choice.upgradeStreet(this);
         }
      }
   }