32. A Complete LLD Mock Interview
Description: A time-boxed prompt requires a defensible, working implementation. Clarify a meeting-room booking problem, model it, implement a slice, run tests, and answer changes.
Episode 32 of 32 | Low-Level Design: From Fundamentals to Interview Practice
Original Java 21 mock LLD interview for a meeting-room booking calendar. Clarified requirements lead to immutable values, explicit identity and replay semantics, atomic local conflict checks, safe cancellation, complete code, bounded concurrency assertions and an actual in-video execution. Authentication, recurring meetings, persistence and distributed coordination are outside scope. Expanded teaching edition: dedicated source-bound purpose, input/result, state/effect, failure, collaboration and concrete-example explanations for every explicitly declared type, constructor and method. Complete source and actual execution retained; no fixed-duration target.
Original script, code, and diagrams. Narration generated locally with the speaker's authorization.
Learning references:
Java 21 Instant reference: https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/time/Instant.html
Chapters
0:00 Welcome and what we will cover
0:13 Mock interview: book a room without double-booking it
0:55 Clarify acceptance, conflicts and retries
1:35 Bound the interview answer and name its limits
2:19 Extract room, slot, booking and calendar responsibilities
3:00 Define associations and the atomic operation boundary
3:42 Defend OOP choices without forcing a pattern catalog
4:29 BookingCalendar: one owner for the cross-booking invariant
6:22 key: give every identity boundary the same meaning
7:59 Room: configuration identity and capacity, not occupancy
9:35 Room constructor: validate the configuration before indexing
11:03 Slot: one valid half-open interval
12:31 Slot constructor: reject malformed time ranges at the boundary
13:54 overlaps: intersection without state changes
15:09 Booking: an immutable observation of identified history
16:33 Booking constructor: local shape is not admission
18:05 Calendar constructor: freeze a consistent room index
19:34 book: replay, validation and publication under one monitor
21:22 cancel: release through replacement, preserve replay history
22:55 snapshot: an ordered copy, not a live status feed
24:25 CalendarTest: connect each guarantee to an executable observation
25:52 check: count success only after verifying the property
27:14 rejects: require the intended exception family
28:40 Test main: boundaries, replay and one controlled contention experiment
30:19 CalendarDemo: actual workflow evidence separated from business logic
31:47 Demo main: follow the admitted identity across cancellation and replay
33:17 Field inventory: configuration, current authority and old observations
34:10 Generated record members and unused default constructors
35:10 Method inventory: where each guarantee is enforced
36:04 Defend the tests without overstating the evidence
37:06 BookingCalendar.java: lines 1-8
38:06 BookingCalendar.java: lines 9-16
40:12 BookingCalendar.java: lines 17-24
41:54 BookingCalendar.java: lines 25-32
43:27 BookingCalendar.java: lines 33-40
45:02 BookingCalendar.java: lines 41-48
46:38 BookingCalendar.java: lines 49-56
48:48 BookingCalendar.java: lines 57-64
50:52 BookingCalendar.java: lines 65-72
52:49 BookingCalendar.java: lines 73-80
54:27 CalendarTest.java: lines 1-8
55:15 CalendarTest.java: lines 9-16
56:16 CalendarTest.java: lines 17-24
57:18 CalendarTest.java: lines 25-32
58:27 CalendarTest.java: lines 33-40
59:55 CalendarTest.java: lines 41-48
1:01:42 CalendarTest.java: lines 49-56
1:02:38 CalendarTest.java: lines 57-64
1:04:19 CalendarTest.java: lines 65-72
1:05:31 CalendarTest.java: lines 73-80
1:06:51 CalendarTest.java: lines 81-81
1:06:54 CalendarDemo.java: lines 1-8
1:07:34 CalendarDemo.java: lines 9-16
1:08:46 CalendarDemo.java: lines 17-24
1:10:12 CalendarDemo.java: lines 25-32
1:12:03 CalendarDemo.java: lines 33-35
1:12:13 Predict the result before the demonstration
1:12:41 Actual admission, replay and interval boundaries
1:13:25 Actual cancellation, safe replay and immutable history
1:14:12 Interview recap: guarantees, limits, and follow-ups
Quick navigation
0:00 welcome
0:13 problem
0:55 requirements
2:19 model
3:00 relationships
3:42 oop patterns
4:29 inventory
37:06 code
1:12:13 demo
1:14:12 recap Close description
Episode 32 of 32 | Low-Level Design: From Fundamentals to Interview Practice
Original Java 21 mock LLD interview for a meeting-room booking calendar. Clarified requirements lead to immutable values, explicit identity and replay semantics, atomic local conflict checks, safe cancellation, complete code, bounded concurrency assertions and an actual in-video execution. Authentication, recurring meetings, persistence and distributed coordination are outside scope. Expanded teaching edition: dedicated source-bound purpose, input/result, state/effect, failure, collaboration and concrete-example explanations for every explicitly declared type, constructor and method. Complete source and actual execution retained; no fixed-duration target.
Original script, code, and diagrams. Narration generated locally with the speaker's authorization.
Learning references:
Java 21 Instant reference: https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/time/Instant.html
Chapters
0:00 Welcome and what we will cover
0:13 Mock interview: book a room without double-booking it
0:55 Clarify acceptance, conflicts and retries
1:35 Bound the interview answer and name its limits
2:19 Extract room, slot, booking and calendar responsibilities
3:00 Define associations and the atomic operation boundary
3:42 Defend OOP choices without forcing a pattern catalog
4:29 BookingCalendar: one owner for the cross-booking invariant
6:22 key: give every identity boundary the same meaning
7:59 Room: configuration identity and capacity, not occupancy
9:35 Room constructor: validate the configuration before indexing
11:03 Slot: one valid half-open interval
12:31 Slot constructor: reject malformed time ranges at the boundary
13:54 overlaps: intersection without state changes
15:09 Booking: an immutable observation of identified history
16:33 Booking constructor: local shape is not admission
18:05 Calendar constructor: freeze a consistent room index
19:34 book: replay, validation and publication under one monitor
21:22 cancel: release through replacement, preserve replay history
22:55 snapshot: an ordered copy, not a live status feed
24:25 CalendarTest: connect each guarantee to an executable observation
25:52 check: count success only after verifying the property
27:14 rejects: require the intended exception family
28:40 Test main: boundaries, replay and one controlled contention experiment
30:19 CalendarDemo: actual workflow evidence separated from business logic
31:47 Demo main: follow the admitted identity across cancellation and replay
33:17 Field inventory: configuration, current authority and old observations
34:10 Generated record members and unused default constructors
35:10 Method inventory: where each guarantee is enforced
36:04 Defend the tests without overstating the evidence
37:06 BookingCalendar.java: lines 1-8
38:06 BookingCalendar.java: lines 9-16
40:12 BookingCalendar.java: lines 17-24
41:54 BookingCalendar.java: lines 25-32
43:27 BookingCalendar.java: lines 33-40
45:02 BookingCalendar.java: lines 41-48
46:38 BookingCalendar.java: lines 49-56
48:48 BookingCalendar.java: lines 57-64
50:52 BookingCalendar.java: lines 65-72
52:49 BookingCalendar.java: lines 73-80
54:27 CalendarTest.java: lines 1-8
55:15 CalendarTest.java: lines 9-16
56:16 CalendarTest.java: lines 17-24
57:18 CalendarTest.java: lines 25-32
58:27 CalendarTest.java: lines 33-40
59:55 CalendarTest.java: lines 41-48
1:01:42 CalendarTest.java: lines 49-56
1:02:38 CalendarTest.java: lines 57-64
1:04:19 CalendarTest.java: lines 65-72
1:05:31 CalendarTest.java: lines 73-80
1:06:51 CalendarTest.java: lines 81-81
1:06:54 CalendarDemo.java: lines 1-8
1:07:34 CalendarDemo.java: lines 9-16
1:08:46 CalendarDemo.java: lines 17-24
1:10:12 CalendarDemo.java: lines 25-32
1:12:03 CalendarDemo.java: lines 33-35
1:12:13 Predict the result before the demonstration
1:12:41 Actual admission, replay and interval boundaries
1:13:25 Actual cancellation, safe replay and immutable history
1:14:12 Interview recap: guarantees, limits, and follow-ups
Quick navigation
0:00 welcome
0:13 problem
0:55 requirements
2:19 model
3:00 relationships
3:42 oop patterns
4:29 inventory
37:06 code
1:12:13 demo
1:14:12 recap Close description