Invalid reservation will result in an exception. Here is a possible list counter is closed, seats are not available, service is cancelled, insufficient funds to purchase, payment gateway is not responding. Create collections or lists of relevant objects. Think of possible objects based on these facts: Bus Company has Routes Routes have Buses Buses have Seats with each seat having a status (occupied or free) Customer should provide the name and payment information. Create a demo app. Implement TicketPurch