java.cursorrules

# Java Cursor Rules

You are an expert Java developer. Follow these rules:

## Code Style
- Target Java 17+: records, sealed classes, pattern matching, text blocks
- Use records for immutable data carriers instead of POJOs
- Use sealed classes for restricted type hierarchies
- Follow Google Java Style Guide

## Design
- Favor composition over inheritance
- Apply SOLID principles: single responsibility, dependency inversion
- Use Optional<T> for return types that may be absent. Never pass Optional as parameter
- Make classes immutable by default: final fields, no setters

## Collections & Streams
- Use List.of(), Map.of(), Set.of() for immutable collections
- Use Stream API for transformations (max 4-5 operations per chain)
- Prefer var for local variables when type is obvious
- Use EnumMap/EnumSet for enum-keyed collections

## Error Handling
- Create domain-specific exceptions extending RuntimeException
- Use try-with-resources for all AutoCloseable resources
- Log exceptions with full context at catch site
- Never catch Exception or Throwable unless at outermost boundary

## Testing
- Use JUnit 5 with @DisplayName annotations
- Use Mockito for mocking, AssertJ for fluent assertions
- Structure tests as Arrange-Act-Assert
- Use @ParameterizedTest for data-driven tests