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jabrenajabrena/cursor-rules-java/skills/141-java-refactoring-with-modern-features/SKILL.md

141-java-refactoring-with-modern-features

Skill452 starsChanged 3 months agoApache-2.0View on GitHub

Use when you need to refactor Java code to adopt modern Java features (Java 8+) — including migrating anonymous classes to lambdas, replacing Iterator loops with Stream API, adopting Optional for null safety, switching from legacy Date/Calendar to java.time, using collection factory methods, applying text blocks, var inference, or leveraging Java 25 features like flexible constructor bodies and module import declarations. This should trigger for requests such as Review Java code for modern Java development; Apply best practices for modern Java development in Java code; Modernize Java code with records pattern matching or switch expressions; Replace legacy idioms with modern Java features; Adopt Java 8+ language features safely. Part of Plinth Toolkit

We split this skill into the rules it gives an agent

11 rules. About 0 are common, 5 are distinctive, and 6 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈5

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 6

    Very specific

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

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Default interface methods, var type inference

    line 19
  2. Distinctive:

    Before applying any modern Java refactoring, ensure the project compiles.

    line 29
  3. Very specific:

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

    line 31
  4. Distinctive:

    SAFETY: If compilation fails, stop immediately — do not proceed until the project compiles successfully

    line 32
  5. Very specific:

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

    line 33
  6. Distinctive:

    BEFORE APPLYING: Read the reference for detailed good/bad examples, constraints, and safeguards for each modern Java feature

    line 34
  7. Distinctive:

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

    line 35
  8. Distinctive:

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

    line 36
  9. Very specific:

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

    line 50
  10. Very specific:

    Read references/141-java-refactoring-with-modern-features.md and identify high-value opportunities to adopt modern Java features.

    line 54
  11. Very specific:

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

    line 62

≈ “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

Modern Java Development Guidelines (Java 8+)

Identify and apply modern Java (Java 8+) refactoring opportunities to improve readability, maintainability, and performance.

What is covered in this Skill?

  • Lambda expressions and method references (over anonymous classes)
  • Stream API for declarative collection processing
  • Optional for null-safe APIs
  • java.time API (replacing Date/Calendar)
  • Default interface methods, var type inference
  • Unmodifiable collection factory methods (List.of(), Set.of(), Map.of())
  • Text blocks for multi-line strings
  • Java 25 Flexible Constructor Bodies (JEP 513)
  • Java 25 Module Import Declarations (JEP 511)

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 modern Java refactoring, ensure the project compiles. If compilation fails, stop immediately — do not proceed until the project compiles successfully. After applying improvements, run full verification.

  • MANDATORY: Run ./mvnw compile or mvn compile before applying any changes
  • SAFETY: If compilation fails, stop immediately — do not proceed until the project compiles successfully
  • VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
  • BEFORE APPLYING: Read the reference for detailed good/bad examples, constraints, and safeguards for each modern Java feature
  • 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 modern Java development
  • Apply best practices for modern Java development in Java code
  • Modernize Java code with records pattern matching or switch expressions
  • Replace legacy idioms with modern Java features
  • Adopt Java 8+ language features safely

Workflow

  1. Compile project before modernization

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

  1. Read modern-Java reference and identify candidates

Read references/141-java-refactoring-with-modern-features.md and identify high-value opportunities to adopt modern Java features.

  1. Apply modern Java refactorings

Refactor incrementally using appropriate language/library features while preserving behavior and readability.

  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/141-java-refactoring-with-modern-features.md.

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