Java Snippets

import java.util.List;
import java.util.stream.Collectors;

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);

// Filter and map
List<Integer> evenSquares = numbers.stream()
    .filter(n -> n % 2 == 0)
    .map(n -> n * n)
    .collect(Collectors.toList());

// Reduce
int sum = numbers.stream()
    .reduce(0, Integer::sum);

// Group by
Map<Boolean, List<Integer>> evenOddGroups = numbers.stream()
    .collect(Collectors.groupingBy(n -> n % 2 == 0));

import java.util.Optional;

class UserService {
    public Optional<User> findById(String id) {
        // Simulated database lookup
        User user = database.find(id);
        return Optional.ofNullable(user);
    }
}

// Usage
UserService service = new UserService();

// Safe chaining
String username = service.findById("123")
    .map(User::getName)
    .orElse("Anonymous");

// With multiple operations
service.findById("123")
    .filter(user -> user.getAge() > 18)
    .ifPresent(user -> sendEmail(user));

// Generic class
public class Box<T> {
    private T content;

    public Box(T content) {
        this.content = content;
    }

    public T getContent() {
        return content;
    }
}

// Generic method
public <T extends Comparable<T>> T findMax(List<T> list) {
    if (list.isEmpty()) {
        throw new IllegalArgumentException("Empty list");
    }

    T max = list.get(0);
    for (T item : list) {
        if (item.compareTo(max) > 0) {
            max = item;
        }
    }
    return max;
}

import java.util.concurrent.CompletableFuture;

public class AsyncService {
    public CompletableFuture<String> fetchData() {
        return CompletableFuture.supplyAsync(() -> {
            // Simulate async operation
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            return "Data";
        });
    }

    // Chaining operations
    public void processData() {
        fetchData()
            .thenApply(data -> data.toUpperCase())
            .thenAccept(System.out::println)
            .exceptionally(error -> {
                System.err.println("Error: " + error);
                return null;
            });
    }
}