# 128 Java Generics

> Use when you need to review, improve, or refactor Java code for generics quality — including avoiding raw types, applying the PECS (Producer Extends Consumer Super) principle for wildcards, using bounded type parameters, designing effective generic methods, leveraging the diamond operator, understanding type erasure implications, handling generic inheritance correctly, preventing heap pollution w…

- **Type:** Skill
- **Install:** `agentstack add skill-jabrena-cursor-rules-java-128-java-generics`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [jabrena](https://agentstack.voostack.com/s/jabrena)
- **Installs:** 0
- **Category:** [Developer Tools](https://agentstack.voostack.com/c/developer-tools)
- **Latest version:** 0.1.0
- **License:** Apache-2.0
- **Upstream author:** [jabrena](https://github.com/jabrena)
- **Source:** https://github.com/jabrena/cursor-rules-java/tree/main/skills/128-java-generics
- **Website:** https://jabrena.github.io/cursor-rules-java/

## Install

```sh
agentstack add skill-jabrena-cursor-rules-java-128-java-generics
```

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

## About

# 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`, `Function`
- 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
- **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

## When to use this skill

- Improve the code with Generics
- Apply Generics
- Refactor the code with Generics

## Workflow

1. **Compile project before generics changes**

Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.

2. **Read generics reference and assess type safety**

Read `references/128-java-generics.md` and identify raw types, unsafe casts, wildcard misuse, and API variance opportunities.

3. **Apply generics refactorings**

Implement selected generic type and API improvements while preserving behavior.

4. **Verify with full build**

Run `./mvnw clean verify` or `mvn clean verify` after applying improvements.

## Reference

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

## Source & license

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

- **Author:** [jabrena](https://github.com/jabrena)
- **Source:** [jabrena/cursor-rules-java](https://github.com/jabrena/cursor-rules-java)
- **License:** Apache-2.0
- **Homepage:** https://jabrena.github.io/cursor-rules-java/

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-jabrena-cursor-rules-java-128-java-generics
- Seller: https://agentstack.voostack.com/s/jabrena
- Browse the marketplace: https://agentstack.voostack.com/browse

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