java-refactor— agent skill

Refactor the Java code I've selected or provided. Follow these steps:

Step 1 — Detect Java version

Check pom.xml (<java.version> or <maven.compiler.source>) or build.gradle (sourceCompatibility). If not found, ask: "What Java version are you targeting? (8, 11, 17, 21, or other)"

Step 2 — Apply safe refactorings (all Java versions)

These refactorings are safe regardless of Java version:

• Extract method: if a method is longer than 20 lines or has a distinct sub-step, extract it with a descriptive name
• Rename for clarity: rename variables, methods, or classes with unclear names
• Remove duplication: identify repeated logic blocks and extract to a shared method
• Replace magic literals: replace inline numbers/strings with named static final constants
• Simplify conditionals: replace nested if/else chains with early returns or ternary where clearer
• Remove dead code: delete unreachable branches, unused variables, unused imports

Step 3 — Apply version-gated refactorings (only if target version supports it)

State the minimum Java version required for each suggestion:

• Java 8+ — Replace anonymous classes with lambdas: e.g., new Comparator<String>() { ... } → (a, b) -> a.compareTo(b)
• Java 8+ — Replace imperative loops with streams: e.g., for-each + list.add → list.stream().filter(...).collect(Collectors.toList())
• Java 8+ — Use Optional instead of null returns: e.g., return null → return Optional.empty()
• Java 9+ — Use List.of / Map.of: e.g., new ArrayList<>(Arrays.asList(...)) → List.of(...)
• Java 10+ — Use var for local variables: where the type is obvious from the right-hand side
• Java 16+ — Replace data classes with records: e.g., a class with only final fields, a constructor, and getters → record
• Java 17+ — Replace instanceof + cast chains with pattern matching: e.g., if (obj instanceof String) { String s = (String) obj; } → if (obj instanceof String s)

Output format

For each refactoring:

1. What: one sentence describing the change
2. Why: one sentence explaining the benefit
3. Before: the original code snippet
4. After: the refactored code snippet
5. Java version required: (e.g., "Java 8+" or "All versions")

Then offer: "Want me to apply these changes to the file?"

Next Steps

After completing refactoring:

• If tests don't exist for the refactored code → suggest running /java-test to generate tests
• If the refactoring changed public API signatures → suggest running /java-docs to update Javadoc
• Remind the user to run their build: mvn compile -q or ./gradlew build -q