Combine coding, system design, communication, and behavioral interview practice.
Interview prep · capstone
Use the strong answer as your reference, explain it aloud in your own words, then choose how soon you want to review it again.
Interview prompt
Strong answer
The final review turns knowledge into performance. A Java backend loop typically combines a coding round, a core Java and Spring deep-dive, a low-level or system design round, and a behavioral round. Practice each under time pressure, out loud, and tie it back to one capstone project you can defend end to end: an order or booking service with a REST API, PostgreSQL with migrations, security, tests with Testcontainers, metrics, and one asynchronous flow with an outbox.
Key points
Interviewer looks for
Interviewers look for structured thinking, honest trade-offs, and ownership: say what you built, why you chose it, what broke, and how you fixed and prevented it.
Java example
1// Capstone low-level design checkpoint: a rate limiter you can explain end to end.
2final class TokenBucket {
3 private final long capacity;
4 private final double refillPerNano;
5 private double tokens;
6 private long lastRefill;
7
8 TokenBucket(long capacity, Duration refillEvery) {
9 this.capacity = capacity;
10 this.refillPerNano = 1.0 / refillEvery.toNanos();
11 this.tokens = capacity;
12 this.lastRefill = System.nanoTime();
13 }
14
15 synchronized boolean tryAcquire() {
16 long now = System.nanoTime();
17 tokens = Math.min(capacity, tokens + (now - lastRefill) * refillPerNano);
18 lastRefill = now;
19 if (tokens < 1) return false;
20 tokens -= 1;
21 return true;
22 }
23}
24// Follow-ups: per-user buckets, distributing it with Redis, and testing with a fake clock.Topic interview questions
These questions are tied to this lesson. Read each question aloud, then compare your explanation with the strong answer.
Strong answer
Restate the problem and confirm constraints and edge cases, propose a brute-force idea and then an optimized approach with time and space complexity, get agreement, write readable code with clear names, and walk through tests including edge cases before declaring it done.
Strong answer
Start with the business goal and main use case, then describe the request flow from controller to service to repository, the data model and migrations, security, the asynchronous flow, testing strategy, and observability. Finish with one trade-off you made and what you would change at higher scale.
Strong answer
Use STAR: briefly set the context, state your responsibility, describe the investigation and evidence that led to the root cause, the fix and how you verified it, and the measurable result. Close with the prevention you added, such as an alert, test, or runbook.
Strong answer
Move bucket state into a shared store such as Redis and perform refill and decrement atomically with a Lua script keyed per client, with a TTL for idle keys. Discuss the latency added per request, behavior when Redis is unavailable (fail open or closed), and clock handling by using server-side time.
Strong answer
Say so honestly, then reason from what you do know: state related principles, propose how you would find out or test it, and give your best hypothesis clearly labelled as such. Interviewers value calibrated reasoning far more than a confident wrong answer.
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