128-java-generics - Claude MCP Skill

# 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
- **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).