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jabrenajabrena/cursor-rules-java/skills/122-java-type-design/SKILL.md

122-java-type-design

Skill452 starsChanged 3 months agoApache-2.0View on GitHub

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. This should trigger for requests such as Review Java code for type design; Improve type design in Java code; Fix primitive obsession in Java code; Create value objects in Java code. Part of Plinth Toolkit

We split this skill into the rules it gives an agent

13 rules. About 0 are common, 8 are distinctive, and 5 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈8

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 5

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Before applying any type design changes, ensure the project compiles.

    line 32
  2. Very specific:

    MANDATORY: Run ./mvnw compile or mvn compile before applying any change

    line 34
  3. Distinctive:

    SAFETY: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition

    line 35
  4. Very specific:

    VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements

    line 36
  5. Distinctive:

    BEFORE APPLYING: Read the reference for detailed examples, good/bad patterns, and constraints

    line 37
  6. Distinctive:

    EDGE CASE: If request scope is ambiguous, stop and ask a clarifying question before applying changes

    line 38
  7. Distinctive:

    EDGE CASE: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance

    line 39
  8. Distinctive:

    Create value objects in Java code

    line 46
  9. Distinctive:

    Create type hierarchies in Java code

    line 47
  10. Distinctive:

    Create fluent interfaces in Java code

    line 48
  11. Very specific:

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

    line 54
  12. Very specific:

    Read references/122-java-type-design.md and identify type hierarchy, naming, and value-object improvements.

    line 58
  13. Very specific:

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

    line 66

≈ “Common” is an estimate: at least 1 in 5 of the 308,232 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

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.

What is covered in this Skill?

  • 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 — 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)
  • Strategic type selection: Optional, Set vs List, interfaces over concrete types

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 type design 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

  • Review Java code for type design
  • Improve type design in Java code
  • Fix primitive obsession in Java code
  • Create value objects in Java code
  • Create type hierarchies in Java code
  • Create fluent interfaces in Java code

Workflow

  1. Compile project before type-design changes

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

  1. Read type-design reference and inspect code

Read references/122-java-type-design.md and identify type hierarchy, naming, and value-object improvements.

  1. Apply type-design refactorings

Implement selected type-safety and readability improvements based on applicable patterns.

  1. Verify with full build

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

Reference

For detailed guidance, examples, and constraints, see references/122-java-type-design.md.

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