Foo.java

        class OrderManager {
            Map<Order, Double> prices;

            double getTotalPrice(Order order) {
                if (prices.containsKey(order)) {
                    return prices.get(order);
                }
                for (Item item : order.getItems()) {
                    //...
                }
                prices.put(order, num);
                return num;
            }
        }