Layered Checkout

Assemble a mini layered system in Solution: - record Order(String id, int cents) (domain) - record OrderView(String id, String total) (DTO — total formatted as "$" + (cents/100) + "." + zeroPadded(cents%100), e.g. $12.05) - interface OrderRepository { void save(Order o); Order findById(String id); } - static class InMemoryOrderRepository implements OrderRepository - static class CheckoutService with constructor (OrderRepository r) and Order place(String id, int cents): rejects negative cents with IllegalArgumentException, then saves and returns the order. - static String viewTotal(int cents) — the mapping function used by OrderView. The controller layer is the test itself: it builds the repo, injects it into the service, places an order, and maps it to a view.

Difficulty: intermediate