java-best-practices

A set of guidelines for writing and reviewing Java 17 or newer code, including modern language features, errors, project layout, and common patterns. Java is a programming language used for applications and services.

In plain words
What is it for?
Use it when building or reviewing Java projects, including records, sealed classes, pattern matching, exception handling, and Maven or Gradle layouts.
Why use it?
It helps avoid unclear code and mishandled resources while encouraging features available in modern Java.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/taoidle/plan-cascade/java
Any agent
npx skills add Taoidle/plan-cascade --skill java
Clone the repo
git clone --depth 1 https://github.com/Taoidle/plan-cascade

Made for: Claude Code, Codex.

Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 499 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00032 $0.00499
Opus 5 $0.00016 $0.00249
Sonnet 5 $0.00006 $0.00100
Haiku 4.5 $0.00003 $0.00050

Measured yesterday against content hash d79ec7988744, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

java-best-practices scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

builtin-skills/java/SKILL.md · 93 lines

What it actually says

Java Best Practices (17+)

Code Style

Rule Guideline
Formatter google-java-format
Analysis SpotBugs, Error Prone
Naming Clear, no abbreviations

Modern Features

Feature Usage
Records Immutable data carriers
Sealed classes Restricted hierarchies
Pattern matching instanceof with binding
var Local type inference
public record User(String id, String name) {}

if (obj instanceof String s && !s.isEmpty()) { process(s); }

public sealed interface Result<T> permits Success, Failure {}
record Success<T>(T value) implements Result<T> {}
record Failure<T>(Exception error) implements Result<T> {}

Error Handling

Rule Guideline
Specific exceptions Not bare Exception
Try-with-resources For AutoCloseable
try (var reader = new BufferedReader(new FileReader(path))) {
    return reader.lines().toList();
} catch (IOException e) {
    throw new ConfigException("Failed: " + path, e);
}

Project Structure

src/main/java/com/example/{domain,service}/
src/test/java/
pom.xml or build.gradle

Common Patterns

Pattern Usage
Optional Null-safe returns
Stream API Functional collections
Builder Complex construction
public Optional<User> findById(String id) {
    return Optional.ofNullable(users.get(id));
}

Anti-Patterns

Avoid Use Instead
Returning null Optional<T>
Mutable data Records
instanceof chains Pattern matching

Testing (JUnit 5 + AssertJ)

@Test void shouldProcess() {
    var service = new Service(mockRepo);
    var result = service.process(input);
    assertThat(result.status()).isEqualTo(SUCCESS);
}
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 93 lines · 32 tokens per session scan A d79ec7988744

Subscribe to this mod's changes

java-best-practices is a skill published in the GitHub repository Taoidle/plan-cascade (124 stars, last pushed 5mo ago), licensed MIT. It adds 32 tokens to every session and 499 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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