name: java-bindings-patterns description: "Instructions for java bindings patterns."

priority: high

Java Bindings Patterns

Role: Java bindings for Rust core. Work on C FFI bridge and Java wrapper packages.

Scope: Java 25 Foreign Function & Memory API (FFM/Panama), Java-idiomatic API, JUnit 5 tests, Javadoc.

Architecture: Java FFM API → C FFI library → Rust core. No JNI, modern Foreign Function API.

Commands: cd packages/java && mvn clean compile test, mvn checkstyle:check, mvn spotless:apply.

E2E Tests: Auto-generated from fixtures via e2e-generator. Regenerate tests when fixtures change.

Critical: Core logic lives in Rust. Java only for FFI bindings/wrappers. If core logic needed, coordinate with Rust team.

Key files: Core.java (high-level API), CoreFFI.java (FFI bindings), config/* (builder pattern), Exception.java (exception hierarchy).

Code quality: Zero Checkstyle/PMD warnings, use mvn checkstyle:check and mvn spotless:apply.

Java 25 Standards & FFM API

• Java 25 exclusively; FFM API for native interop, sealed classes, records, pattern matching
• Build: Maven (pom.xml) or Gradle (build.gradle.kts); compiler release=25
• JUnit 5: @Nested classes, @ParameterizedTest, AssertJ fluent assertions, 80%+ coverage
• Checkstyle: 4-space indent, line <=120 chars, Javadoc on public APIs
• PMD: UnusedVariable, EmptyCatchBlock, AvoidDuplicateLiterals enabled
• FFM patterns: Arena for memory management, try-with-resources, bounds validation
• Naming: PascalCase (classes), camelCase (methods/fields), UPPER_SNAKE_CASE (constants)
• Best practices: final on classes/methods, immutable records, Optional<T> not null