Java25 Coding Conventions Training

Key things the skill must make very clear:

• Records for all data-carrying classes (not manual immutable classes)
• Sealed interfaces for closed type hierarchies
• Switch expressions with pattern matching for type dispatch
• List.copyOf / List.of instead of Collections.unmodifiable*
• final var (never bare var)
• Stream.toList() instead of Collectors.toList()
• Text blocks for multi-line strings

Step 2: Validate with test cases

After regenerating, validate the skill using the test cases in evals/evals.json.

For each test case, spawn a subagent that:

1. Reads the general skill from plugins/conventions/skills/java-coding-conventions/SKILL.md
2. Reads the generated Java 25 skill from plugins/conventions/skills/java25-coding-conventions/SKILL.md
3. Reads any input files specified in the test case
4. Completes the task described in the prompt, following both skills' conventions
5. Writes output Java files to a workspace directory

Then run the shared grading script against the outputs:

cd plugins/training
python -m shared.grade <workspace-dir>

The script checks Java 25-specific assertions:

• Uses records for data classes
• Uses sealed interfaces for type hierarchies
• Uses pattern matching (not instanceof + cast)
• Uses switch expressions with arrows
• Uses modern collection factories (List.of, List.copyOf)
• No outdated Java 8 patterns (Collections.unmodifiable*, Collectors.toList)
• Uses final var where appropriate

Plus general assertions (final vars, immutable fields, small methods, etc.).

Expected results

All assertions should pass for all test cases. If any fail, the conventions in the skill need strengthening in that area.

Test cases

The test cases in evals/evals.json cover:

1. Refactor ShapeCalculator — old-style instanceof, abstract hierarchy, manual string building, old collections
2. Refactor ApiResponse — manually-written immutable class, string concatenation, old collections, if-else chains
3. Greenfield Event Processing — sealed interface with record subtypes, pattern matching, streams

Input files for refactoring tests are in evals/files/.

Conventions reference

The authoritative conventions are in references/conventions.md. Always read that file when regenerating — it is the single source of truth for what Java 25-specific rules to include.