Why This Matters

Java and Kotlin benefit from Copilot's strong training coverage — the JVM ecosystem is well-represented. Knowing the modern features (records, sealed classes, Kotlin data classes) gets you the best suggestions.

Concept Explained

Copilot recognizes Maven/Gradle projects, JUnit 5 conventions, Spring Boot annotations, and modern Java/Kotlin features. Type-rich signatures (records, data classes) drive better suggestions than traditional POJOs.

How It Works

When Copilot sees Java records or Kotlin data classes, it suggests idiomatic usage. Spring Boot annotations (@RestController, @Service) trigger Copilot to suggest corresponding Spring patterns. JUnit 5 is the default for /tests.

Step-by-Step Tutorial

1. Use Java records

2. Kotlin data classes

3. Spring annotations

4. JUnit 5 with /tests

5. Maven/Gradle

Real-World Example

A Java developer defined `public record User(String id, String name, String email) {}` and asked Copilot to write a UserController. Copilot suggested a complete Spring @RestController with CRUD endpoints, using the record's accessor methods. Saved 30 minutes of boilerplate.

Example Prompts / Commands / Code

public record User(String id, String name, String email) {
    // Copilot recognizes record, suggests:
    //   - accessor methods (id(), name(), email())
    //   - equals, hashCode, toString auto-generated
    //   - immutable usage patterns
}

// Copilot suggests:
public List<User> findActiveUsers(List<User> users) {
    return users.stream()
        .filter(User::active)
        .toList();
}

@RestController
@RequestMapping("/api/users")
public class UserController {
    // Copilot suggests:
    //   @GetMapping
    //   public List<User> list() { ... }
    //
    //   @GetMapping("/{id}")
    //   public User get(@PathVariable String id) { ... }
    //
    //   @PostMapping
    //   public User create(@RequestBody User user) { ... }
}

Common Mistakes

• Using old-style POJOs instead of records — more boilerplate, worse Copilot output.
• Mixing Kotlin and Java without configuring Copilot hints.
• Forgetting JUnit 5 — Copilot may default to JUnit 4 if pom.xml is old.
• Not using Spring annotations — Copilot can't suggest Spring patterns.

Best Practices

• Use Java records (14+) for immutable data.
• Use Kotlin data classes for the same in Kotlin.
• Annotate Spring components — Copilot matches patterns.
• Ensure JUnit 5 in pom.xml/build.gradle for /tests.
• Ask for 'idiomatic Kotlin' or 'idiomatic Java' explicitly.

Troubleshooting

Practical Exercise

Frequently Asked Questions

Further Reading

• Copilot in JetBrains IDEs

Official References

• Copilot in JetBrains

Related lessons: BE-37, BE-38