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.

**Prerequisites:** Run `./mvnw compile` or `mvn compile` before applying any change. If compilation fails, **stop immediately** and do not proceed — compilation failure is a blocking condition.

**Core areas:** Type safety (avoiding raw types, eliminating unsafe casts), code reusability (generic methods and types for multiple type contexts), API clarity (PECS wildcards — `? extends` for producers, `? super` for consumers), performance optimization (eliminating boxing/casting overhead), 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 with `Comparator<? super T>` and `Function<? super T, ? extends R>`, arrays-vs-generics covariance pitfalls, serialization with `TypeReference`/`TypeToken`, eliminating unchecked warnings, generic naming conventions (`T`, `E`, `K/V`, `?`), typesafe heterogeneous containers, and integration with Records, sealed types, and pattern matching.

**Scope:** The reference is organized by examples (with good/bad code patterns) for each core area. Apply recommendations based on applicable examples; validate compilation before changes and run `./mvnw clean verify` or `mvn clean verify` after applying improvements.

**Before applying changes:** Read the reference for detailed examples, good/bad patterns, and constraints.

## Reference

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