What is 121-java-object-oriented-design?

Guidance for reviewing and improving object-oriented Java code. It covers class and interface design, SOLID, DRY, YAGNI, inheritance, composition, dependency injection, and common code smells.

Use it to refactor large classes, improve interfaces, choose between composition and inheritance, design object creation, or address smells such as God Class and Feature Envy.

It helps reduce tangled responsibilities, weak encapsulation, duplicated logic, and unnecessary abstractions. The recommendations are selected according to the specific design problem in the code.

121-java-object-oriented-design — Skill by jabrena/plinth

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.

Any agent

npx skills add jabrena/plinth --skill 121-java-object-oriented-design

Clone the repo

git clone --depth 1 https://github.com/jabrena/plinth

Made for: Claude Code, Codex.

Its marketplace also offers this one on its own, as the plugin 121-java-object-oriented-design — /plugin install 121-java-object-oriented-design after adding the marketplace above.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/jabrena/plinth/121-java-object-oriented-design/github.svg)](https://agentmods.dev/skills/jabrena/plinth/121-java-object-oriented-design)

Your own site

<a href="https://agentmods.dev/skills/jabrena/plinth/121-java-object-oriented-design"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/121-java-object-oriented-design/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/jabrena/plinth/121-java-object-oriented-design"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/121-java-object-oriented-design.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 107 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,746 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

Socket pass 26 Sept 2026
Snyk pass 26 Sept 2026
NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00107	$0.01746
Opus 5.5	$0.00043	$0.00698
Sonnet 5.5	$0.00021	$0.00349
Haiku 4.5	$0.00011	$0.00175

Measured 23d ago against content hash 835e4fc79321, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

121-java-object-oriented-design 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 23d ago.

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.

skills/121-java-object-oriented-design/SKILL.md · 127 lines

How it starts

The opening of the file, as written. The whole thing — 127 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Java Object-Oriented Design Guidelines

Review and improve Java code using focused object-oriented design references selected after assessing the request and affected code.

What is covered in this Skill?

Fundamental design principles (SOLID, DRY, YAGNI)
Class and interface design: composition over inheritance, immutability, accessibility minimization, accessor methods
Core OOP concepts: encapsulation, inheritance, polymorphism
Object creation patterns: static factory methods, Builder, Singleton, dependency injection, avoiding unnecessary objects
OOD code smells: God Class, Feature Envy, Inappropriate Intimacy, Refused Bequest, Shotgun Surgery, Data Clumps
Method design: parameter validation, defensive copies, careful signatures, empty collections over nulls, Optional usage
Exception handling: checked vs. runtime exceptions, standard exceptions, failure-capture messages, no silent ignoring

Scope: Classify the applicable OOD concerns first, then load only the focused references needed for those concerns. Load multiple references when a refactoring crosses concern boundaries.

Constraints

Before applying any OOD changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.

MANDATORY: Run ./mvnw compile or mvn compile before applying any change
SAFETY: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
PROGRESSIVE DISCLOSURE: Classify the applicable OOD concerns before reading references, then read only the references mapped to those concerns
MULTI-CONCERN CHANGES: Read multiple focused references only when the request or diagnosed code problems cross concern boundaries
PRESERVE BEHAVIOR: Apply focused, incremental refactorings without changing observable business behavior
INCREMENTAL SAFETY: Compile after each significant refactoring and keep changes easy to revert if validation reveals a regression
DEPENDENCY SAFETY: Confirm refactoring does not break imports, dependencies, class relationships, or established contracts
ADJACENT SKILLS: Use skill 122 for dedicated type-design work and skill 126 for dedicated exception-handling work; use the overlapping skill 121 references only when those topics are part of a broader OOD review
EDGE CASE: If request scope is ambiguous, stop and ask a clarifying question before applying changes
EDGE CASE: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance

Read the full file on GitHub · 127 lines

Files

What ships with it

8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

23d ago Changed 835e4fc79321
1mo ago First seen · 127 lines · 107 tokens per session scan A dc727522f1cb

Subscribe to this mod's changes

121-java-object-oriented-design is a skill published in the GitHub repository jabrena/plinth (454 stars, last pushed yesterday), licensed Apache-2.0. It adds 107 tokens to every session and 1,746 once invoked, about $0.0004 per session on Opus 5.5. 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 2026-09-03.

Claude Code Code review Java Languages claude-code-skills claude-skills cursor-ai github-copilot

phx-review

Review changed Elixir/Phoenix code read-only. Check requirements, cite evidence, deduplicate findings, and return a severity-based verdict.

oliver-kriska/claude-elixir-phoenix · 32 tokens

solid-principles

SOLID principles checklist with Java examples. Use when a class has too many responsibilities, an abstraction leaks, or a dependency points the wrong way, and when the user asks about Single Responsibility, Open/Closed, Liskov, Interface Segregation or Dependency Inversion. For naming, duplication and method length…

decebals/claude-code-java · 73 tokens

concurrency-review

Review Java concurrency code for thread safety, race conditions, deadlocks, and modern patterns (Virtual Threads, CompletableFuture, @Async). Use when user asks "check thread safety", "concurrency review", "async code review", or when reviewing multi-threaded code.

decebals/claude-code-java · 58 tokens

java-code-review

Systematic code review for Java with null safety, exception handling, concurrency, and performance checks. Use when user says "review code", "check this PR", "code review", or before merging changes.

decebals/claude-code-java · 45 tokens

java-api-consistency-validator

Validate API consistency between two versions of Java libraries. Use when you need to compare API behavior, signatures, and exceptions between Java library versions to identify breaking changes, incompatible modifications, and behavior differences. The skill performs static analysis of Java code, compares method…

ArabelaTso/Skills-4-SE · 95 tokens

ts-audit

Audit TypeScript and React code against expert-level best practices from 9 TypeScript library references. Use when the user wants to review, audit, check, or improve TypeScript code quality — including requests like "audit this file", "review my types", "check my TypeScript", "what's wrong with this code", "improve my…

chrislacey89/skills · 141 tokens