Java

Java beyond the syntax — JVM internals, GC, virtual threads, the modern language features, and the ecosystem.

How OpenJDK is organised, how JEPs move features from draft to shipped, and what preview/incubator/experimental stability levels promise.

The JDK vs the JRE, and one note per JDK command-line tool, from javac to jdb.

The JVM spec and its implementations compared — HotSpot, OpenJ9, GraalVM, Azul — plus the GraalVM deep dive.

The map of Java memory — where objects live, the lifecycle from allocation to reclamation, and how the memory-model and GC notes fit together.

The three ways to build — bare JDK tools, Maven, Gradle — and the artifact formats they produce.

Spring, Quarkus and Micronaut deep dives, plus the Jakarta EE correspondence table.

Testing strategies and their tooling — unit, integration, E2E, mutation, property-based, performance, security.

Protocol implementations per stack — REST, GraphQL, gRPC, WebSockets, and messaging.

Storage access by kind — relational, Redis, document/NoSQL, time series, graph — across the frameworks.

Application security per stack — OAuth2/OIDC, web security, and cryptography with the JCA.

The house reference for structuring a hexagonal service in Java — a Maven/Gradle modulith whose module graph is the architecture, one hexagon per bounded context under modules/, composed into runnable assemblies under application/ — with per-layer implementation guidelines.

Practice material: katas, challenges, build projects.