Java — policy & pitfalls

Baseline knowledge of the Java language (records, sealed, pattern matching, text blocks, streams, var, generics, Optional API) is assumed — this skill does not teach the language. It encodes the project policy and the traps that keep appearing in code review.

Setup Check (run first)

Before writing non-trivial code, verify:

1. JDK version — java --version, and target version in pom.xml (<maven.compiler.release>) or build.gradle(.kts) (java { toolchain { languageVersion = JavaLanguageVersion.of(21) } }). Adjust feature use if < 17. Current LTS: Java 25 (released Sept 2025); Java 21 is the previous LTS. Prefer LTS releases for new projects.
2. Build tool wrapper — use ./mvnw / ./gradlew, never a globally installed mvn / gradle.
3. Lombok — look for lombok in dependencies. If present, prefer @RequiredArgsConstructor / @Slf4j / @Builder; if absent, do not introduce Lombok unless asked.
4. Static analysis — error-prone, checkstyle, spotbugs, pmd. Respect existing rules; do not add new violations.
5. Preview features — if build uses --enable-preview, some features behave differently. Check flag before relying on preview syntax.

MUST DO