Interview Handbooks

Interview prep for software engineers at senior, staff, and principal level — with a backend focus on the Java & Kotlin ecosystem. Clear explanations, real examples, and a curated Q&A bank with strong, ready-to-say answers.

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Why this exists

These handbooks lean toward the backend and the Java & Kotlin ecosystem — the JVM, Spring, persistence, messaging, and the distributed systems built on top of them — alongside the architecture, operations, and people skills that senior+ rounds actually test.

Even in the AI era, the fundamentals still decide who gets the offer. AI can generate code, but it can’t replace an engineer who understands why — who knows how a HashMap resizes, why a queue beats a synchronous call, what an error budget protects, and how to reason about consistency under failure. Tools change; the principles you’re hired to apply do not. This library is about knowing them deeply enough to explain, defend, and act on them — in an interview and on the job.

The library

Data & Storage

PostgreSQL MVCC, indexing, HOT updates, locking, partitioning.

Redis Data types, persistence, eviction, clustering, patterns.

Elasticsearch Inverted index, analyzers, shards, scoring, aggregations.

Messaging & APIs

Kafka vs RabbitMQ Log vs broker, delivery semantics, ordering, when to use which.

gRPC & Protobuf IDL, wire format, streaming, backward compatibility.

API Design & GraphQL REST, versioning, idempotency, pagination, GraphQL, gRPC tradeoffs.

Backend

Spring Boot IoC/DI, bean lifecycle, auto-config, AOP, transactions.

Ktor (vs Spring Boot) Coroutine-native Kotlin framework: engines, plugins, async, and a Spring Boot comparison.

Hibernate & JPA Entity lifecycle, lazy loading, N+1, caching, transactions.

JVM Internals Memory model, GC, class loading, concurrency (Java & Kotlin).

Language Tricky Points Object/Any methods, equals/hashCode, == vs ===, strings, Integer cache, clone/copy, serialization.

Java & Kotlin Data Structures Collections internals, complexity, versions, HashMap vs TreeMap, Kotlin sequences.

Algorithms: Sort & Search Sorting/searching, complexity, pros & cons, and how Java/Kotlin/Spring use them.

Java & Kotlin Concurrency Memory model, locks, atomics, executors, virtual threads, coroutines.

Async & Reactive Programming Event loop, backpressure, Reactor, coroutines, virtual threads vs reactive.

Architecture & Infrastructure

System Design Scaling, caching, queues, consistency, real walkthroughs.

Distributed Systems Theory CAP/PACELC, consistency, consensus, clocks, quorums, CRDTs.

Microservices Decomposition, Saga, Outbox, CQRS, resilience, observability.

Docker Images, layers, networking, volumes, Compose.

Kubernetes Architecture, controllers, networking, scaling, rollouts.

Nginx & Load Balancing Reverse proxy, LB algorithms, L4 vs L7, TLS, caching.

Security · Tooling · AI/ML

OAuth2 & JWT Flows, PKCE, OIDC, token validation, attacks & defenses.

Git The object model, branching, rebase vs merge, recovery.

LLM Engineering Prompting, RAG, agents, evaluation, production concerns.

Operations & Quality

Observability & SRE Metrics/logs/traces, SLO/SLI, error budgets, RED/USE, incidents.

CI/CD & Deployment Pipelines, blue-green/canary, feature flags, migrations, DORA.

Testing Strategy Test pyramid, doubles, flaky tests, contract testing, coverage myths.

Career & Leadership

Staff Behavioral & Leadership Scope, influence without authority, STAR stories, judgment, incidents.

Soft Skills & Communication Communication, feedback, conflict, collaboration, mentoring.