ShoppingCart.java

import java.util.*;

public class ShoppingCart{
   private ArrayList<Item> order;
   private double total;
   private double internalDiscount;

   public ShoppingCart(){
      order = new ArrayList<Item>();
      total = 0.0;
      internalDiscount = 0.0;
   }

   public void add(Item i) {
      order.add(i);
      total += i.getPrice();
      if (i instanceof DiscountedItem)
         internalDiscount += ((DiscountedItem) i).getDiscount();
   }

     /** printOrder() will call toString() to print */
   public void printOrder() {
      System.out.println(this);
   }

   public String toString() {
      return discountToString();
   }

   public String discountToString() {
      return orderToString() + "\nSub-total: " + valueToString(total) + "\nDiscount: " + valueToString(internalDiscount) + "\nTotal: " + valueToString(total - internalDiscount);
   }

   private String valueToString(double value) {
      value = Math.rint(value * 100) / 100.0;
      String result = "" + Math.abs(value);
      if(result.indexOf(".") == result.length() - 2) {
         result += "0";
      }
      result = "$" + result;
      return result;
   }

   public String orderToString() {
      String build = "\nOrder Items:\n";
      for(int i = 0; i < order.size(); i++) {
         build += "   " + order.get(i);
         if(i != order.size() - 1) {
            build += "\n";
         }
      }
      return build;
   }
}