Java Collections Framework: Structures, Generics & Algorithms

import java.util.*;

public class ListShowcase {
    public static void main(String[] args) {
        // ArrayList: Ideal for read-heavy workloads
        List<String> techStack = new ArrayList<>();
        techStack.add("Java 21");
        techStack.add("Spring Boot");
        techStack.add("PostgreSQL");
        techStack.add(1, "Docker"); // Inserts at index 1, shifts elements right

        System.out.println("Random Access [index 2]: " + techStack.get(2));

        // LinkedList: Ideal for frequent front/rear insertions
        LinkedList<String> pipeline = new LinkedList<>(techStack);
        pipeline.addFirst("Git Checkout");
        pipeline.addLast("Deploy Kubernetes");

        System.out.println("First stage: " + pipeline.getFirst());
        System.out.println("Total Pipeline Size: " + pipeline.size());
    }
}

import java.util.*;

// 1. Entity implementing Comparable for Natural Sorting (by Price)
class Product implements Comparable<Product> {
    private final String sku;
    private final String name;
    private final double price;

    public Product(String sku, String name, double price) {
        this.sku = sku;
        this.name = name;
        this.price = price;
    }

    public String getName() { return name; }
    public double getPrice() { return price; }

    @Override
    public int compareTo(Product other) {
        return Double.compare(this.price, other.price);
    }

    @Override
    public String toString() {
        return String.format("[%s] %s ($%.2f)", sku, name, price);
    }
}

// 2. Customer Order for Priority Processing
class CustomerOrder {
    public enum Tier { STANDARD, PREMIUM, VIP }

    private final String orderId;
    private final Tier tier;
    private final double totalAmount;

    public CustomerOrder(String orderId, Tier tier, double totalAmount) {
        this.orderId = orderId;
        this.tier = tier;
        this.totalAmount = totalAmount;
    }

    public String getOrderId() { return orderId; }
    public Tier getTier() { return tier; }
    public double getTotalAmount() { return totalAmount; }

    @Override
    public String toString() {
        return String.format("Order(%s | %s | $%.2f)", orderId, tier, totalAmount);
    }
}

// 3. Execution Controller
public class OrderDispatchEngine {
    public static void main(String[] args) {
        System.out.println("==================================================");
        System.out.println("   DEVASCENT COLLECTIONS DISPATCH & ROUTING ENGINE  ");
        System.out.println("==================================================");

        // A. TreeSet: Auto-Sorted Catalog (Natural Ordering via Comparable)
        TreeSet<Product> catalog = new TreeSet<>();
        catalog.add(new Product("SKU-101", "Mechanical Keyboard", 129.99));
        catalog.add(new Product("SKU-102", "4K Ultra Monitor", 449.50));
        catalog.add(new Product("SKU-103", "Ergonomic Mouse", 59.00));

        System.out.println("--- Sorted Product Catalog (Ascending Price) ---");
        for (Product p : catalog) {
            System.out.println("  • " + p);
        }

        // B. PriorityQueue with Custom Comparator (VIP Tier first, then Order Amount desc)
        Comparator<CustomerOrder> dispatchComparator = Comparator
                .comparing(CustomerOrder::getTier, Comparator.reverseOrder())
                .thenComparing(CustomerOrder::getTotalAmount, Comparator.reverseOrder());

        PriorityQueue<CustomerOrder> orderQueue = new PriorityQueue<>(dispatchComparator);
        orderQueue.offer(new CustomerOrder("ORD-101", CustomerOrder.Tier.STANDARD, 85.00));
        orderQueue.offer(new CustomerOrder("ORD-102", CustomerOrder.Tier.VIP, 120.00));
        orderQueue.offer(new CustomerOrder("ORD-103", CustomerOrder.Tier.PREMIUM, 350.00));
        orderQueue.offer(new CustomerOrder("ORD-104", CustomerOrder.Tier.VIP, 920.00));

        System.out.println("\n--- Dispatching Priority Orders ---");
        while (!orderQueue.isEmpty()) {
            System.out.println("  🚀 Dispatched: " + orderQueue.poll());
        }

        // C. ListIterator: Safe Traversal and Modification
        List<String> warehouseBays = new ArrayList<>(
                Arrays.asList("Bay-A1", "Bay-B2", "Bay-C3", "Bay-D4")
        );
        ListIterator<String> it = warehouseBays.listIterator();
        while (it.hasNext()) {
            String bay = it.next();
            if (bay.equals("Bay-B2")) {
                it.set("Bay-B2-MAINTENANCE"); // In-place mutation safely
            }
        }
        System.out.println("\nUpdated Warehouse Bays: " + warehouseBays);
        System.out.println("==================================================");
    }
}