Controller

@RestController
@RequestMapping("/theater")
@RequiredArgsConstructor
public class TheaterController {
    private final TheaterService theaterService;

    @GetMapping("hello")
    public String welcomeMessage(){
        return "Welcome to The Wanted Theater";
    }

    @GetMapping("enter")
    public String enter(){
        return theaterService.enter();
    }
}

Service

@Service
@RequiredArgsConstructor
public class TheaterService {
private final Theater theater;
	public String enter(){
	    theater.enter(new Audience(new Bag(1000L)),
	            new TicketSeller(new TicketOffice(20000L, new Ticket(100L))));
	    return "Have a good time.";
	
	}
}

Handler

public class Audience {
    private final Bag bag;

    public Audience(Bag bag){
        this.bag = bag;
    }

    public Bag getBag(){ return bag;}
}

public class Bag {
    private Long amount;
    private final Invitation invitation;
    private Ticket ticket;

    public Bag(long amount){
        this(null, amount);
    }
    public Bag(Invitation invitation, long amount){
        this.invitation = invitation;
        this.amount = amount;
    }

    public boolean hasInvitation() {
        return invitation != null;
    }
    public boolean hasTicket() {
        return ticket != null;
    }
    public void setTicket(Ticket ticket) {
        this.ticket = ticket;
    }
    public void minusAmount(long amount) {
        this.amount -= amount;
    }
    public void plusAmount(long amount) {
        this.amount += amount;
    }
}

public class Invitation {
    private LocalDateTime when;
}

@Component
@RequiredArgsConstructor
public class Theater {

    public void enter(Audience audience, TicketSeller ticketSeller){
        if(audience.getBag().hasInvitation()){
            Ticket ticket = ticketSeller.getTicketOffice().getTicket();
            audience.getBag().setTicket(ticket);
        }else {
            Ticket ticket = ticketSeller.getTicketOffice().getTicket();
            audience.getBag().minusAmount(ticket.getFee());
            ticketSeller.getTicketOffice().plusAmount(ticket.getFee());
            audience.getBag().setTicket(ticket);
        }
    }
}

public class Ticket {
    private Long fee;

    public Ticket(Long fee) {
        this.fee = fee;
    }

    public Long getFee() {
        return fee;
    }
}

public class TicketOffice {
    private long amount;
    private final List<Ticket> tickets;

    public TicketOffice(Long amount, Ticket ... tickets) {
        this.amount = amount;
        this.tickets = Arrays.asList(tickets);
    }

    public Ticket getTicket(){
        return tickets.get(0);
    }

    public void minusAmount(long amount) {
        this.amount -= amount;
    }
    public void plusAmount(long amount) {
        this.amount += amount;
    }
}

public class TicketSeller {
    private final TicketOffice ticketOffice;

    public TicketSeller(TicketOffice ticketOffice){
        this.ticketOffice = ticketOffice;
    }

    public TicketOffice getTicketOffice(){
        return ticketOffice;
    }
}