128-java-generics

A reference for using Java generics, the type parameters that let code work with different data types while keeping compile-time checks. It covers type-safe APIs, wildcards, bounds, inheritance, arrays, and type erasure.

In plain words
What is it for?
Use it when reviewing, designing, or refactoring Java generic classes, methods, collections, builders, or APIs. It also covers patterns involving records, sealed types, serialization, and pattern matching.
Why use it?
It helps prevent raw types, unsafe casts, and confusing type relationships in Java code. The guidance makes reusable code safer and easier to understand.

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/jabrena/cursor-rules-examples/128-java-generics
Any agent
npx skills add jabrena/cursor-rules-examples --skill 128-java-generics
Clone the repo
git clone --depth 1 https://github.com/jabrena/cursor-rules-examples

Made for: Claude Code, Codex.

Per session 105 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 596 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 $0.00105 $0.00596
Opus 5 $0.00053 $0.00298
Sonnet 5 $0.00021 $0.00119
Haiku 4.5 $0.00011 $0.00060

Measured yesterday against content hash a411cae0b377, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

128-java-generics 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.

.agents/skills/128-java-generics/SKILL.md · 47 lines

How it starts

The opening of the file, as written. The whole thing — 47 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Java Generics Best Practices

Review and improve Java code using comprehensive generics best practices that enforce compile-time type safety and enable flexible, reusable APIs.

What is covered in this Skill?

  • Type safety: avoiding raw types, eliminating unsafe casts
  • Code reusability: generic methods and types for multiple type contexts
  • PECS wildcards: ? extends for producers, ? super for consumers
  • Diamond operator for type inference
  • Type erasure awareness: type tokens, factory patterns, array creation
  • Generic inheritance and variance: invariance, covariance, contravariance
  • @SafeVarargs for heap pollution prevention
  • Wildcard capture helpers, self-bounded generics (CRTP) for fluent builders
  • Proper wildcard API design: Comparator<? super T>, Function<? super T, ? extends R>
  • Arrays-vs-generics covariance pitfalls, serialization with TypeReference/TypeToken
  • Generic naming conventions (T, E, K/V, ?), typesafe heterogeneous containers
  • Integration with Records, sealed types, and pattern matching

Scope: The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

Constraints

Before applying any generics 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
  • BEFORE APPLYING: Read the reference for detailed examples, good/bad patterns, and constraints

When to use this skill

  • Review Java code for generics
  • Apply best practices for generics in Java code

Reference

For detailed guidance, examples, and constraints, see references/128-java-generics.md.

Read the full file on GitHub · 47 lines

Files

What ships with it

1 file 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.

  1. yesterday First seen · 47 lines · 105 tokens per session scan A a411cae0b377

Subscribe to this mod's changes

128-java-generics is a skill published in the GitHub repository jabrena/cursor-rules-examples (2 stars, last pushed 5d ago), licensed Apache-2.0. It adds 105 tokens to every session and 596 once invoked, about $0.0005 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 2026-08-31.

Related

Other skills, from other repositories

complexity

Wire and satisfy cyclomatic complexity lint. Detect the repo's existing linter, set or keep a cap (default 10), extract until green, never disable the rule. Use when complexity.mdc globs match, lint reports C901/complexity, or the user asks for simpler / less nested code.

kleosr/kleosrules · 66 tokens

uikit-expert

Write, review, or improve UIKit code following best practices for view controller lifecycle, Auto Layout, collection views, navigation, animation, memory management, and modern iOS 18–26 APIs. Use when building new UIKit features, refactoring existing views or view controllers, reviewing code quality, adopting modern…

zinxj/uikit-expert-skill · 95 tokens

debugging

Debugs difficult, intermittent, cross-layer, or regression bugs evidence before fixes. Use when the cause is unknown, normal debugging stalled, or the user asks to hunt, diagnose, or root-cause a bug.

kleosr/kleosrules · 46 tokens

redesign-existing-projects

Elaya audit for existing sites/apps that look generic, cheap, or AI-made. Diagnose first, then fix in place (fonts, color, states, layout, motion). Use when Mario says polish, audit, upgrade, or it looks horrible. Product apps apply diagnosis through premium-ui-craft values, not Elaya black/Geist/700ms. Upstream…

kleosr/kleosrules · 92 tokens

testing

Test writing workflows: TDD order, mocks, house gauntlet, regression naming. Use when writing/editing tests or when testing.mdc globs match. Thin rule = roofs; this skill = procedure.

kleosr/kleosrules · 45 tokens

design-stack

Router for Mario's Design agent. Picks one UI skill plus premium-ui-craft. Use at the start of any Product Designer / @Design / UX/UI turn.

kleosr/kleosrules · 36 tokens