Java

Modern Java development with Java 17+ features, streams, and enterprise patterns.

When to Use

• Working with .java files
• Building enterprise applications with Spring Boot
• Android development with Kotlin interop
• Microservices architecture

Quick Start

// Modern record with validation
public record User(String id, String name, String email) {
    public User {
        Objects.requireNonNull(id, "id must not be null");
        Objects.requireNonNull(name, "name must not be null");
    }
}

Core Concepts

Records (Java 17+)

// Immutable data carriers
public record User(String id, String name, String email) {
    // Compact constructor for validation
    public User {
        Objects.requireNonNull(id, "id must not be null");
    }

    // Additional methods
    public String displayName() {
        return name.toUpperCase();
    }
}

Sealed Classes

public sealed interface Result<T> permits Success, Failure {
    T getOrThrow();
}

public record Success<T>(T value) implements Result<T> {
    @Override
    public T getOrThrow() { return value; }
}

public record Failure<T>(Exception error) implements Result<T> {
    @Override
    public T getOrThrow() { throw new RuntimeException(error); }
}

Common Patterns

Streams & Collections

// Immutable collections
var list = List.of("a", "b", "c");
var map = Map.of("key1", "value1", "key2", "value2");

// Stream operations
List<String> names = users.stream()
    .filter(User::active)
    .map(User::name)
    .sorted()
    .toList();

// Collectors grouping
Map<String, List<User>> byRole = users.stream()
    .collect(Collectors.groupingBy(User::role));

Optional

Optional<User> user = Optional.ofNullable(findUser(id));

String name = user
    .map(User::name)
    .orElse("Unknown");

user.ifPresentOrElse(
    u -> process(u),
    () -> handleMissing()
);

Best Practices

Do:

• Use var for local variables with obvious types
• Prefer records for data transfer objects
• Use Optional instead of null checks
• Use virtual threads for I/O-bound tasks (Java 21+)

Don’t:

• Use raw types for collections (use generics)
• Use Optional.get() without checking
• Catch generic Exception (be specific)
• Create mutable DTOs unnecessarily

Troubleshooting

References

• Java Official Docs
• Baeldung