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java-development

Day-to-day plain Java development without a framework: Maven and Gradle usage and wrappers, project layout, dependency and vulnerability management, modern Java idioms by JDK version (records, sealed types, pattern matching, virtual threads), SLF4J logging, error and null handling, immutability, concurrency basics, static analysis and formatting (Spotless, Error Prone, -Xlint), packaging (jar, jlink, jpackage) and GitHub Actions CI. Use when writing, building, reviewing or maintaining ordinary Java code.

skills/java-development/SKILL.md

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# Java Development (plain Java)

Everyday guidance for Java projects that are not tied to a framework. If the project uses Spring Boot, Quarkus, Helidon or similar, prefer that framework's skills for framework concerns and use this one for the plain-Java parts.

## Rules that always apply

1. **Detect before you write.** Read `pom.xml`/`build.gradle*`, `.mvn/`, `gradle/`, `.java-version`/`.sdkmanrc`, `.editorconfig`, CI files, and a few source files. Match the build tool, Java release, formatter, naming, logging and test libraries already in use.
2. **Never upgrade implicitly.** Do not change the Java release, build-tool version, plugin or dependency versions, or add a formatter/linter/static analyzer the project lacks, as a side effect of another task. Suggest it and ask. Version upgrades are their own task (`java-upgrade`, if installed).
3. **Use the wrapper** (`./mvnw`, `./gradlew`) when present; otherwise the installed `mvn`/`gradle`. Do not commit a wrapper unprompted.
4. **Verify with a build.** After any change run the project's own verification (`./mvnw -B verify` or `./gradlew build`) and report the result. Run a narrower command first while iterating. If you could not run it, say so.
5. **Ask the user** before: changing public APIs or serialized/DB/wire formats, raising the Java release, adding runtime dependencies, adding tools to the build, deleting or weakening tests, changing CI, or when two reasonable designs have different trade-offs.
6. Prefer the standard library and small, explicit code over new dependencies. No Lombok unless already used.

## Pick idioms by the project's Java release