java-best-practices

A Conductor skill providing guidance for writing type-safe, concurrent, and modern Java code targeting Java 17+ and Java 21 LTS.

Overview

This skill activates when working with Java files and provides guidance on:

• Type Safety: Optional usage, @Nullable/@NonNull annotations, defensive coding patterns
• Concurrency: CompletableFuture, virtual threads (Java 21), ExecutorService, thread safety
• Modern Features: Records, sealed classes, pattern matching, switch expressions

Target Versions

• Java 17 LTS: Records, sealed classes, pattern matching for instanceof
• Java 21 LTS: Virtual threads, pattern matching in switch, sequenced collections

Activation

The skill automatically activates when:

• Working with .java files
• Working with pom.xml or build.gradle files
• Task description contains keywords: java, optional, completablefuture, record, sealed, virtual thread
• Project tech stack includes Java

Patterns Provided

| Pattern | Description | |---------|-------------| | type-safety | Optional best practices, null safety annotations, defensive coding | | concurrency | CompletableFuture, virtual threads, thread-safe patterns | | modern-features | Records, sealed classes, pattern matching |

Usage Examples

Type-Safe Optional Handling

// Good - explicit Optional handling
public Optional<User> findUserById(String id) {
    return Optional.ofNullable(userRepository.findById(id));
}

// Usage with map/flatMap
String userName = findUserById("123")
    .map(User::getName)
    .orElse("Unknown");

Modern Records

// Immutable data carrier with automatic equals, hashCode, toString
public record User(String id, String name, String email) {
    // Compact constructor for validation
    public User {
        Objects.requireNonNull(id, "id cannot be null");
        Objects.requireNonNull(name, "name cannot be null");
    }
}

Virtual Threads (Java 21)

// Lightweight threads for IO-bound operations
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    List<Future<String>> futures = urls.stream()
        .map(url -> executor.submit(() -> fetchUrl(url)))
        .toList();

    for (Future<String> future : futures) {
        System.out.println(future.get());
    }
}

Related Skills

• testing-strategies: For Java testing patterns with JUnit 5
• api-design: For REST API development with Spring Boot or Jakarta EE

Changelog

1.0.0

• Initial release
• Type safety patterns with Optional and null annotations
• Concurrency patterns with CompletableFuture and virtual threads
• Modern Java features (records, sealed classes, pattern matching)