The three recoveries

1. static CompletableFuture<String> recovered() — async throwing IllegalStateException; recover with exceptionally returning "fallback". 2. static CompletableFuture<String> handled() — same failing async; recover with handle returning "fallback" on error, "ok:" + result on success. 3. static CompletableFuture<String> observed() — a SUCCEEDING async ("value"), with whenComplete appending to a static List<String> observations (add "saw-value" on success) — return the future; the observation must exist after join. 4. static CompletableFuture<String> onTimeoutFallback() — async sleeping 200ms then returning "late"; bound with completeOnTimeout("fast-fail", 20, MILLISECONDS).

Difficulty: advanced