Solution: Order Processing Pipeline

import java.util.concurrent.CompletableFuture;
public class OrderPipeline {
    public static void main(String[] args) {
        int orderId = 101;
        System.out.println("Starting order pipeline...");
        // 1. Build the pipeline chain
        CompletableFuture<Void> pipeline = CompletableFuture.supplyAsync(() -> fetchOrder(orderId))
            .thenApply(order -> processPayment(order))      // Transform Order -> Payment
            .thenApply(payment -> generateInvoice(payment)) // Transform Payment -> String (Invoice)
            .thenAccept(invoice -> System.out.println(invoice)); // Consume String
        // 2. Wait for completion
        // We use join() to block the main thread until the entire chain finishes.
        pipeline.join();
        System.out.println("Main thread finished.");
    }
    // --- Helper Methods ---
    static Order fetchOrder(int id) {
        System.out.println("1. Fetching Order #" + id + "...");
        sleep(500);
        return new Order(id, 150.00);
    }
    static Payment processPayment(Order order) {
        System.out.println("2. Processing Payment for Order #" + order.id + "...");
        sleep(500);
        return new Payment(order, "PAID-" + System.currentTimeMillis());
    }
    static String generateInvoice(Payment payment) {
        System.out.println("3. Generating Invoice...");
        sleep(500);
        return "INVOICE: Order " + payment.order.id + " | Amount $" + payment.order.amount + " | Status: " + payment.transactionId;
    }
    static void sleep(int ms) {
        try { Thread.sleep(ms); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
    }
    record Order(int id, double amount) {}
    record Payment(Order order, String transactionId) {}
}