Q12 state: advance() x3 -> NEW -> PAID -> SHIPPED -> DELIVERED
Q12 state: advance() on DELIVERED -> IllegalStateException: already delivered
Q12 strategy: total(1000) with NONE=1000.0 then FESTIVAL=900.0
Q13 sort by length (Comparator strategy): [fig, pear, banana]
Q13 sort reversed alphabetical: [pear, fig, banana]
Q13 inline lambda strategy: total(200)=150.0
Q14 publishNaive, 2 listeners, first unsubscribes itself: delivered to [first] (no exception, second was skipped)
Q14 publishNaive, 3 listeners, first unsubscribes itself -> ConcurrentModificationException
Q14 publishSafe, two events, self-unsubscribing listener: [once, other, other]
Q14 java.util.Observable @Deprecated(since="9")
Q15 template method run(): [open, sales rows, close]
Q15 strategy version runWith(): [open, ad-hoc rows, close]
Q15 run() is final (subclasses cannot reorder the steps): true
Q16 valid request   -> 200 ok via [auth, rate-limit, controller]
Q16 no token        -> 401 via [auth]
Q17 after two commands: "Hello, world"; undo -> "Hello"; undo -> ""
Q18 2 + 3 * 4 via sealed switch=14 via Visitor=14