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.

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.

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.

Multi-step scope: Step 1 validates the project compiles. Step 2 analyzes Java code to identify generics issues categorized by impact (CRITICAL, MAINTAINABILITY, PERFORMANCE, TYPE_SAFETY) and area (raw types, wildcard misuse, bounded parameter opportunities, type erasure problems, modern feature integration gaps). Step 3 eliminates raw types and unsafe casts with proper parameterization. Step 4 applies PECS wildcards and bounded type parameters for flexible APIs. Step 5 introduces diamond operator, generic methods, and type tokens for type erasure scenarios. Step 6 integrates generics with Records, sealed types, and pattern matching. Step 7 validates all changes compile and all tests pass with ./mvnw clean verify.

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.