# Writing Java Kotlin

> Idiomatic modern Java and Kotlin JVM development. Use when writing `.java`,

- **Type:** Skill
- **Install:** `agentstack add skill-alexei-led-cc-thingz-writing-java-kotlin`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [alexei-led](https://agentstack.voostack.com/s/alexei-led)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [alexei-led](https://github.com/alexei-led)
- **Source:** https://github.com/alexei-led/cc-thingz/tree/master/dist/codex/plugins/programming/skills/writing-java-kotlin

## Install

```sh
agentstack add skill-alexei-led-cc-thingz-writing-java-kotlin
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Java and Kotlin Development

Use only for Java/Kotlin JVM code and JVM build files. Follow the project's JDK,
Kotlin, Gradle/Maven, framework, test stack, formatter, static-analysis config,
and local conventions.

## Read First

Read [principles.md](references/principles.md) before writing, changing, or reviewing Java/Kotlin code. Read conditional references only when the change touches that area.

## Conditional References

- [patterns.md](references/patterns.md) — package/module layout, Spring/Ktor/service boundaries, nullability, concurrency, persistence, and build seams.
- [testing.md](references/testing.md) — adding or reshaping JUnit, Kotest, Mockito/MockK, Spring, or Gradle/Maven tests; keep the local loop fast.
- [linting.md](references/linting.md) — JDK/tool installation, Gradle/Maven toolchains, formatters, ktlint, detekt, Spotless, and slow-check policy.
- [cli.md](references/cli.md) — writing or changing JVM CLIs.

## Project Baseline

- Inspect `gradle/wrapper/gradle-wrapper.properties`, `settings.gradle*`, `build.gradle*`, `pom.xml`, `.mvn/`, `gradle.properties`, CI, and nearby code before using version-specific Java, Kotlin, or plugin behavior.
- Prefer the project wrapper: `./gradlew` before global `gradle`; `./mvnw` before global `mvn`.
- Use the configured Java toolchain and Kotlin `jvmToolchain`. Do not assume the shell's newest JDK is the compile target.
- Prefer the JDK/Kotlin stdlib and existing dependencies before adding a library.
- Keep domain code free of framework, persistence, HTTP, and DI types unless the project already chose that coupling.

## Version-Gated APIs

- Java 21+: records, sealed types, pattern matching, switch expressions, and virtual threads are available when the project toolchain allows them.
- Java 25+: treat new platform APIs as available only when Gradle/Maven toolchains and CI target 25 or newer.
- Preview features require explicit user or project approval and a visible compiler/test flag.
- Kotlin: follow the configured Kotlin language/API version. Do not use a Kotlin 2.x feature unless the build already enables it.

## Comments, Javadoc, and KDoc

- Use Javadoc or KDoc for visible public APIs when the project expects generated docs.
- Keep API docs to a useful summary, contract, edge case, or effect. Do not restate names and signatures.
- Omit comments for simple obvious getters, overrides, and data holders when there is nothing useful to add.
- Add implementation comments only for non-obvious constraints, invariants, side effects, tradeoffs, or framework quirks.
- Keep comments short. Move longer rationale to docs, issue links, or design notes.
- Do not comment obvious code.
- Keep tests readable without comments; add one only for unobvious fixtures, timing, concurrency, framework setup, or regression context.

## Verification

Run focused module tests and format/lint while editing, then the project-configured build, tests, lint, static analysis, and formatting checks before final output. Prefer Gradle/Maven test filtering over full-suite runs in the hot loop.

If a check is unavailable, state that and run the closest configured gate. If a
check fails, quote the failure, diagnose the cause, fix one issue, and rerun the
relevant check.

## Failure Cases

- No clear JVM root: locate the nearest `settings.gradle*`, `build.gradle*`, or `pom.xml` before choosing commands or package names.
- Unknown JDK or Kotlin target: inspect toolchains, compiler options, CI, and wrapper versions before using newer APIs or syntax.
- New dependency requested: confirm the JDK/Kotlin stdlib or existing dependencies cannot meet the requirement.
- Slow checks by default: switch to focused Gradle/Maven filters or file-scoped format/lint; reserve broad checks for final verification.
- Broad or risky edit: state the risk and ask before acting. Do not run destructive commands.

## Final Response

Include:

- changed files
- checks run and results
- checks skipped with reasons
- remaining risks or follow-ups

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [alexei-led](https://github.com/alexei-led)
- **Source:** [alexei-led/cc-thingz](https://github.com/alexei-led/cc-thingz)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-alexei-led-cc-thingz-writing-java-kotlin
- Seller: https://agentstack.voostack.com/s/alexei-led
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.