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122-java-type-design

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Use when you need to review, improve, or refactor Java code for type design quality — including establishing clear type hierarchies, applying consistent naming conventions, eliminating primitive obsession with domain-specific value objects, leveraging generic type parameters, creating type-safe wrappers, designing fluent interfaces, ensuring precision-appropriate numeric types (BigDecimal for financial calculations), and improving type contrast through interfaces and method signature alignment.

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Source SKILL.md: https://github.com/majiayu000/claude-skill-registry/blob/HEAD/skills/development/skills-jabrena-cursor-rules-java-17/SKILL.md

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Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

Type Design Thinking in Java

Review and improve Java code using comprehensive type design principles that apply typography concepts to code structure and organization for maximum clarity and maintainability.

Core areas: Clear type hierarchies (nested static classes, logical structure), consistent naming conventions (domain-driven patterns, uniform interface/implementation naming), strategic whitespace for readability, type-safe wrappers (value objects replacing primitive obsession, EmailAddress, Money), generic type parameters (flexible reusable types, bounded parameters), domain-specific fluent interfaces (builder pattern, method chaining), type "weights" (conceptual importance assignment — core domain vs supporting vs utility), type contrast through interfaces (contract vs implementation separation), aligned method signatures (consistent parameter and return types across related classes), self-documenting code (clear descriptive names), BigDecimal for precision-sensitive calculations (financial/monetary operations), and strategic type selection (Optional, Set vs List, interfaces over concrete types).

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 type design issues categorized by impact (CRITICAL, MAINTAINABILITY, TYPE_SAFETY, READABILITY) and area (naming conventions, type hierarchies, generic usage, primitive obsession, type safety, precision). Step 3 applies naming convention improvements and type hierarchy restructuring. Step 4 eliminates primitive obsession by creating domain-specific value objects and records. Step 5 introduces proper generic type parameters with appropriate bounds and type-safe wrappers. Step 6 implements precision-appropriate numeric types and strategic collection/type selection. 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/122-java-type-design.md.