A ten-stage Java roadmap for 2026 built on Java 25 and Spring Boot 4.1: what to learn at each stage, how to know you are ready to move on, a visual map, a runnable tour file and links to the matching guides.
A system design interview solved with running code: a URL shortener on Spring Boot 4.1 with base62 codes, block-allocated ids, a Feistel scrambler, Redis cache-aside with negative caching, a Lua token-bucket rate limiter and 24 passing tests.
A low-level design interview solved end to end in Java 25: requirements, entities, Strategy and Observer patterns, lock-free concurrency, real output and 10 passing tests. Full code in the companion repository.
The five SOLID principles in Java 25, each shown as a violating design, the real output that proves it hurts, and the refactored code. Includes a class diagram, one-line interview answers and a runnable file.
Scenario-based Java interview questions for developers with about five years of experience: lost updates, deadlocks, mutable HashMap keys, ThreadLocal leaks, parallel streams, CompletableFuture and production debugging. Eight bugs reproduced in a downloadable Java file with real output, plus 32 answered questions.
50 SQL interview queries with answers for Java developers: Nth highest salary, duplicates, joins, GROUP BY and HAVING, window functions, recursive CTEs and indexes. One sample schema, every query run on PostgreSQL 16 with its real result, plus a downloadable SQL file.
40 scenario-based Kafka interview questions with short answers: ordering, acks and replication, rebalancing, lag, exactly-once, dead-letter topics and share groups. Claims are verified against a real Kafka 4.4.0 broker with downloadable Java files and their actual output.
40 microservices interview questions with short answers and the trap behind each, plus seven patterns (retry, circuit breaker, idempotency, saga, outbox, rate limiting, correlation id) that run for real in a downloadable Java 25 file with its actual output.
A runnable Spring Boot 4.1 microservices project: Spring Cloud Gateway, Eureka, Config Server, product/order/inventory services, a Resilience4j circuit breaker and tracing, with real output.
A complete Spring Boot 4.1 CRUD REST API on a real MySQL 8.4 server: entity, repository, service, controller, validation, ProblemDetail errors, Flyway, with real curl requests and responses.