complex

Simple:
Old: https://pastebin.com/bsXH7eHU

Exp 1: entry/exit loop
import java.util.ArrayList;
import java.util.Scanner;

public class ECommerceLoopingDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        ArrayList<String> shoppingCart = new ArrayList<>();

        int choice;

        do {
            System.out.println("E-Commerce Shopping Cart:");
            System.out.println("1. Add item to cart");
            System.out.println("2. Remove item from cart");
            System.out.println("3. View cart");
            System.out.println("4. Checkout");
            System.out.println("5. Exit");
            System.out.print("Enter your choice: ");
            choice = scanner.nextInt();

            switch (choice) {
                case 1:
                    System.out.print("Enter the item to add: ");
                    String itemToAdd = scanner.next();
                    shoppingCart.add(itemToAdd);
                    System.out.println(itemToAdd + " added to the cart.");
                    break;

                case 2:
                    System.out.print("Enter the item to remove: ");
                    String itemToRemove = scanner.next();
                    if (shoppingCart.contains(itemToRemove)) {
                        shoppingCart.remove(itemToRemove);
                        System.out.println(itemToRemove + " removed from the cart.");
                    } else {
                        System.out.println("Item not found in the cart.");
                    }
                    break;

                case 3:
                    System.out.println("Shopping Cart Contents:");
                    for (String item : shoppingCart) {
                        System.out.println("- " + item);
                    }
                    break;

                case 4:
                    if (shoppingCart.isEmpty()) {
                        System.out.println("Your cart is empty. Cannot proceed to checkout.");
                    } else {
                        System.out.println("Checkout Successful!");
                        shoppingCart.clear();
                    }
                    break;

                case 5:
                    System.out.println("Exiting the program.");
                    break;

                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        } while (choice != 5);

        scanner.close();
    }
}

Exp 2: nesting of switch statement
import java.util.Scanner;

public class ECommerceOrderProcessing {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int orderState = 0;
        boolean orderComplete = false;

        while (!orderComplete) {
            System.out.println("E-Commerce Order Processing System:");
            System.out.println("1. New Order");
            System.out.println("2. Order Processing");
            System.out.println("3. Shipped");
            System.out.println("4. Delivered");
            System.out.println("5. Cancel Order");
            System.out.println("6. Exit");
            System.out.print("Enter your choice: ");
            int action = scanner.nextInt();

            switch (orderState) {
                case 0: // New Order
                    switch (action) {
                        case 1:
                            System.out.println("Order placed. Awaiting processing.");
                            orderState = 1;
                            break;
                        case 6:
                            orderComplete = true;
                            break;
                        default:
                            System.out.println("Invalid action for the current order state.");
                            break;
                    }
                    break;

                case 1: // Order Processing
                    switch (action) {
                        case 2:
                            System.out.println("Order is being processed.");
                            orderState = 2;
                            break;
                        case 5:
                            System.out.println("Order canceled.");
                            orderState = 0;
                            break;
                        case 6:
                            orderComplete = true;
                            break;
                        default:
                            System.out.println("Invalid action for the current order state.");
                            break;
                    }
                    break;

                case 2: // Shipped
                    switch (action) {
                        case 3:
                            System.out.println("Order has been shipped.");
                            orderState = 3;
                            break;
                        case 5:
                            System.out.println("Order canceled.");
                            orderState = 0;
                            break;
                        case 6:
                            orderComplete = true;
                            break;
                        default:
                            System.out.println("Invalid action for the current order state.");
                            break;
                    }
                    break;

                case 3: // Delivered
                    switch (action) {
                        case 4:
                            System.out.println("Order has been delivered. Thank you for your purchase!");
                            orderState = 0;
                            break;
                        case 5:
                            System.out.println("Order canceled.");
                            orderState = 0;
                            break;
                        case 6:
                            orderComplete = true;
                            break;
                        default:
                            System.out.println("Invalid action for the current order state.");
                            break;
                    }
                    break;

                default:
                    System.out.println("Invalid order state.");
                    break;
            }
        }

        System.out.println("Exiting the order processing system.");
        scanner.close();
    }
}

Exp 3: single and multi dimensional arrays
import java.util.Scanner;

public class Lab3 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Single-dimensional array to represent a product catalog
        String[] products = {
            "Product A",
            "Product B",
            "Product C",
            "Product D",
            "Product E"
        };

        // Multi-dimensional array to represent a shopping cart (product, quantity)
        String[][] shoppingCart = new String[5][2];
        int cartSize = 0;

        boolean shopping = true;

        while (shopping) {
            System.out.println("E-Commerce Product Catalog:");
            for (int i = 0; i < products.length; i++) {
                System.out.println((i + 1) + ". " + products[i]);
            }
            System.out.println("6. View Cart");
            System.out.println("7. Checkout");
            System.out.println("8. Exit");
            System.out.print("Enter your choice: ");
            int choice = scanner.nextInt();

            if (choice >= 1 && choice <= products.length) {
                System.out.print("Enter the quantity: ");
                int quantity = scanner.nextInt();
                if (quantity > 0) {
                    shoppingCart[cartSize][0] = products[choice - 1];
                    shoppingCart[cartSize][1] = String.valueOf(quantity);
                    cartSize++;
                    System.out.println("Item added to the cart.");
                } else {
                    System.out.println("Quantity must be greater than 0.");
                }
            } else {
                switch (choice) {
                    case 6:
                        System.out.println("Shopping Cart Contents:");
                        for (int i = 0; i < cartSize; i++) {
                            System.out.println(shoppingCart[i][0] + " (Quantity: " + shoppingCart[i][1] + ")");
                        }
                        break;
                    case 7:
                        System.out.println("Checkout Successful!");
                        cartSize = 0;
                        break;
                    case 8:
                        System.out.println("Exiting the program.");
                        shopping = false;
                        break;
                    default:
                        System.out.println("Invalid choice. Please try again.");
                        break;
                }
            }
        }

        scanner.close();
    }
}

Exp 4: constructor & method overloading
class Product {
    private int productId;
    private String productName;
    private double price;

    // Default constructor
    public Product() {
        productId = 0;
        productName = "No Product";
        price = 0.0;
    }

    // Constructor with product name and price
    public Product(String productName, double price) {
        this.productId = generateProductId();
        this.productName = productName;
        this.price = price;
    }

    // Constructor with all attributes
    public Product(int productId, String productName, double price) {
        this.productId = productId;
        this.productName = productName;
        this.price = price;
    }

    // Method to display product details
    public void displayProduct() {
        System.out.println("Product ID: " + productId);
        System.out.println("Product Name: " + productName);
        System.out.println("Price: $" + price);
    }

    // Method overloading: Calculate and display discounted price
    public void displayProduct(double discountPercentage) {
        double discountedPrice = price - (price * discountPercentage / 100);
        System.out.println("Product ID: " + productId);
        System.out.println("Product Name: " + productName);
        System.out.println("Price: $" + price);
        System.out.println("Discounted Price: $" + discountedPrice);
    }

    // Generate a unique product ID (for demonstration purposes)
    private int generateProductId() {
        // In a real e-commerce system, this would be a more sophisticated logic
        return (int) (Math.random() * 1000);
    }
}

public class Lab4 {
    public static void main(String[] args) {
        // Create products using overloaded constructors
        Product product1 = new Product();
        Product product2 = new Product("Laptop", 799.99);
        Product product3 = new Product(1001, "Smartphone", 299.99);

        // Display product details using overloaded methods
        product1.displayProduct();
        System.out.println();

        product2.displayProduct();
        System.out.println();

        product3.displayProduct(10); // 10% discount
    }
}

Exp 5: static keyword
class Product {
    private int productId;
    private String productName;
    private double price;

    // Static variable to keep track of the total number of products
    private static int totalProducts = 0;

    public Product(String productName, double price) {
        this.productId = generateProductId();
        this.productName = productName;
        this.price = price;
        totalProducts++;
    }

    public void displayProduct() {
        System.out.println("Product ID: " + productId);
        System.out.println("Product Name: " + productName);
        System.out.println("Price: $" + price);
    }

    // Static method to get the total number of products
    public static int getTotalProducts() {
        return totalProducts;
    }

    // Generate a unique product ID (for demonstration purposes)
    private int generateProductId() {
        // In a real e-commerce system, this would be a more sophisticated logic
        return (int) (Math.random() * 1000);
    }
}

public class ECommerceWithStatic {
    public static void main(String[] args) {
        // Create products and display product details
        Product product1 = new Product("Laptop", 799.99);
        Product product2 = new Product("Smartphone", 299.99);

        product1.displayProduct();
        System.out.println();

        product2.displayProduct();
        System.out.println();

        // Get the total number of products using the static method
        int totalProducts = Product.getTotalProducts();
        System.out.println("Total Products in the Store: " + totalProducts);
    }
}

Exp 6: multi-level inheritance
// Base class representing a product
class Product {
    private String name;
    private double price;

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

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }

    public void displayProductInfo() {
        System.out.println("Product: " + name);
        System.out.println("Price: $" + price);
    }
}

// Subclass representing electronic products
class Electronics extends Product {
    private String brand;

    public Electronics(String name, double price, String brand) {
        super(name, price);
        this.brand = brand;
    }

    public String getBrand() {
        return brand;
    }

    @Override
    public void displayProductInfo() {
        super.displayProductInfo();
        System.out.println("Brand: " + brand);
    }
}

// Subclass representing laptops
class Laptop extends Electronics {
    private String processor;

    public Laptop(String name, double price, String brand, String processor) {
        super(name, price, brand);
        this.processor = processor;
    }

    public String getProcessor() {
        return processor;
    }

    @Override
    public void displayProductInfo() {
        super.displayProductInfo();
        System.out.println("Processor: " + processor);
    }
}

public class Multi {
    public static void main(String[] args) {
        // Create a Laptop object
        Laptop laptop = new Laptop("Dell XPS 13", 1299.99, "Dell", "Intel Core i7");

        // Display product information
        laptop.displayProductInfo();
    }
}

Exp 7: super & this keyword
class Product {
    public int productId;
    public String productName;
    public double price;

    public Product(int productId, String productName, double price) {
        this.productId = productId;
        this.productName = productName;
        this.price = price;
    }

    public void displayProduct() {
        System.out.println("Product ID: " + productId);
        System.out.println("Product Name: " + productName);
        System.out.println("Price: $" + price);
    }

    public double getPrice() {
        return price;
    }
}

class DiscountedProduct extends Product {
    public double discount;

    public DiscountedProduct(int productId, String productName, double price, double discount) {
        super(productId, productName, price);
        this.discount = discount;
    }

    public void displayProductWithDiscount() {
        super.displayProduct();
        System.out.println("Discount: " + discount + "%");
        double discountedPrice = getPrice() - (getPrice() * discount / 100);
        System.out.println("Discounted Price: $" + discountedPrice);
    }
}

public class Lab7 {
    public static void main(String[] args) {
        Product product = new Product(1, "Laptop", 799.99);
        DiscountedProduct discountedProduct = new DiscountedProduct(2, "Smartphone", 299.99, 10.0);

        System.out.println("Product Details:");
        product.displayProduct();
        System.out.println();

        System.out.println("Discounted Product Details:");
        discountedProduct.displayProductWithDiscount();
    }
}

Exp 8: abstract & final keywords
import java.util.Scanner;

abstract class ECommerceProduct {
    private String name;
    private double price;

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

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }

    public abstract void displayProductDetails();
}

final class Book extends ECommerceProduct {
    private String author;
    private int numberOfPages;

    public Book(String name, double price, String author, int numberOfPages) {
        super(name, price);
        this.author = author;
        this.numberOfPages = numberOfPages;
    }

    @Override
    public void displayProductDetails() {
        System.out.println("Book Details:");
        System.out.println("Name: " + getName());
        System.out.println("Price: " + getPrice());
        System.out.println("Author: " + author);
        System.out.println("Number of Pages: " + numberOfPages);
    }
}

public class Exp8 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter the book name: ");
        String bookName = scanner.nextLine();

        System.out.println("Enter the book price: ");
        double bookPrice = scanner.nextDouble();

        System.out.println("Enter the book author: ");
        String bookAuthor = scanner.nextLine();

        System.out.println("Enter the number of pages in the book: ");
        int bookNumberOfPages = scanner.nextInt();

        Book book = new Book(bookName, bookPrice, bookAuthor, bookNumberOfPages);

        book.displayProductDetails();
        scanner.close();
    }
}

Exp 9: methods of String class
public class Exp9 {

    public static void main(String[] args) {
        String productTitle = "Apple iPhone 13 Pro";

        // Get the length of the product title
        int productTitleLength = productTitle.length();
        System.out.println("Product title length: " + productTitleLength);

        // Get the first character of the product title
        char firstChar = productTitle.charAt(0);
        System.out.println("First character of the product title: " + firstChar);

        // Get the last character of the product title
        int lastIndex = productTitle.length() - 1;
        char lastChar = productTitle.charAt(lastIndex);
        System.out.println("Last character of the product title: " + lastChar);

        // Check if the product title contains the word "Apple"
        boolean containsApple = productTitle.contains("Apple");
        System.out.println("Product title contains the word 'Apple': " + containsApple);

        // Replace the word "iPhone" with the word "Smartphone" in the product title
        String newProductTitle = productTitle.replace("iPhone", "Smartphone");
        System.out.println("New product title: " + newProductTitle);

        // Convert the product title to lowercase
        String lowercaseProductTitle = productTitle.toLowerCase();
        System.out.println("Lowercase product title: " + lowercaseProductTitle);

        // Convert the product title to uppercase
        String uppercaseProductTitle = productTitle.toUpperCase();
        System.out.println("Uppercase product title: " + uppercaseProductTitle);
    }
}

Exp 10: exception handling
import java.util.ArrayList;
import java.util.Scanner;

public class Exp10 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        ProductRepository productRepository = new ProductRepository();

        System.out.println("Enter the product name: ");
        String productName = scanner.nextLine();

        try {
            addProductToCart(productRepository, productName);
        } catch (ECommerceException e) {
            System.out.println(e.getMessage());
            scanner.close();
        }
    }

    public static void addProductToCart(ProductRepository productRepository, String productName) throws ECommerceException {
        // Check if the product exists.
        if (!ProductRepository.containsProduct(productName)) {
            throw new ECommerceException("Product does not exist.");
        }

        // Get the product from the repository.
        Product product = ProductRepository.getProduct(productName);

        // Check if the product is in stock.
        if (!product.isInStock()) {
            throw new ECommerceException("Product is out of stock.");
        }

        // Add the product to the cart.
        // ...
    }
}

class ECommerceException extends Exception {

    public ECommerceException(String message) {
        super(message);
    }
}

class ProductRepository {

    private static ArrayList<Product> products = new ArrayList<>();

    public static void addProduct(Product product) {
        products.add(product);
    }

    public static Product getProduct(String productName) {
        for (Product product : products) {
            if (product.getName().equals(productName)) {
                return product;
            }
        }
        return null;
    }

    public static boolean containsProduct(String productName) {
        return getProduct(productName) != null;
    }
}

class Product {

    private String name;
    private double price;
    private int stockLevel;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getStockLevel() {
        return stockLevel;
    }

    public void setStockLevel(int stockLevel) {
        this.stockLevel = stockLevel;
    }

    public boolean isInStock() {
        return stockLevel > 0;
    }
}

Exp 11: interface (packages aren't here)
import java.util.ArrayList;
import java.util.List;

public interface Exp11 {
    void addProductToCart(String productName) throws ECommerceException;
    void removeProductFromCart(String productName) throws ECommerceException;
    void checkout() throws ECommerceException;
}

class ECommerceServiceImpl implements Exp11 {

    private ShoppingCart shoppingCart;

    public ECommerceServiceImpl() {
        this.shoppingCart = new ShoppingCart();
    }

    @Override
    public void addProductToCart(String productName) throws ECommerceException {
        // Check if the product exists.
        if (!ProductRepository.containsProduct(productName)) {
            throw new ECommerceException("Product does not exist.");
        }

        // Check if the product is in stock.
        Product product = ProductRepository.getProduct(productName);
        if (!product.isInStock()) {
            throw new ECommerceException("Product is out of stock.");
        }

        // Add the product to the cart.
        shoppingCart.addProduct(product);
    }

    @Override
    public void removeProductFromCart(String productName) throws ECommerceException {
        // Check if the product is in the cart.
        Product product = shoppingCart.getProduct(productName);
        if (product == null) {
            throw new ECommerceException("Product is not in the cart.");
        }

        // Remove the product from the cart.
        shoppingCart.removeProduct(product);
    }

    @Override
    public void checkout() throws ECommerceException {
        // Check if the cart is empty.
        if (shoppingCart.isEmpty()) {
            throw new ECommerceException("Cart is empty.");
        }

        // Process the checkout.
        // ...
    }
}

class ECommerceException extends Exception {

    public ECommerceException(String message) {
        super(message);
    }
}

class ShoppingCart {

    private List<Product> products;

    public ShoppingCart() {
        this.products = new ArrayList<>();
    }

    public void addProduct(Product product) {
        products.add(product);
    }

    public Product getProduct(String productName) {
        for (Product product : products) {
            if (product.getName().equals(productName)) {
                return product;
            }
        }
        return null;
    }

    public void removeProduct(Product product) {
        products.remove(product);
    }

    public boolean isEmpty() {
        return products.isEmpty();
    }
}

class Product {

    private String name;
    private double price;
    private int stockLevel;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getStockLevel() {
        return stockLevel;
    }

    public void setStockLevel(int stockLevel) {
        this.stockLevel = stockLevel;
    }

    public boolean isInStock() {
        return stockLevel > 0;
    }
}

MASTER:
import java.util.Scanner;

// Abstract class representing a product
abstract class Product {
    String name;
    double price;

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

    // Abstract method
    abstract void displayProductInfo();
}

// Intermediate class inheriting from Product
class Electronics extends Product {
    String brand;

    Electronics(String name, double price, String brand) {
        super(name, price);
        this.brand = brand;
    }

    @Override
    void displayProductInfo() {
        System.out.println("Product: " + name);
        System.out.println("Price: $" + price);
        System.out.println("Brand: " + brand);
    }
}

// Final class inheriting from Electronics
final class Laptop extends Electronics {
    String processor;

    Laptop(String name, double price, String brand, String processor) {
        super(name, price, brand);
        this.processor = processor;
    }

    @Override
    void displayProductInfo() {
        super.displayProductInfo();
        System.out.println("Processor: " + processor);
    }
}

public class Master {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Welcome to the E-Commerce Store!");
        System.out.print("Enter the name of the laptop: ");
        String laptopName = scanner.nextLine();
        System.out.print("Enter the price of the laptop: ");
        double laptopPrice = scanner.nextDouble();
        scanner.nextLine(); // Consume the newline character
        System.out.print("Enter the brand of the laptop: ");
        String laptopBrand = scanner.nextLine();
        System.out.print("Enter the processor of the laptop: ");
        String laptopProcessor = scanner.nextLine();

        Laptop laptop = new Laptop(laptopName, laptopPrice, laptopBrand, laptopProcessor);

        System.out.println("\nProduct Information:");
        laptop.displayProductInfo();

        scanner. Close();
    }
}

Interface:
// Interface representing a generic product
interface Product {
    String getName();
    double getPrice();
    void displayProductInfo();
}

// Interface representing electronic products
interface Electronics extends Product {
    String getBrand();
}

// Interface representing laptops
interface Laptop extends Electronics {
    String getProcessor();
}

// Concrete class implementing the Laptop interface
class DellLaptop implements Laptop {
    private String name;
    private double price;
    private String brand;
    private String processor;

    public DellLaptop(String name, double price, String brand, String processor) {
        this.name = name;
        this.price = price;
        this.brand = brand;
        this.processor = processor;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public double getPrice() {
        return price;
    }

    @Override
    public String getBrand() {
        return brand;
    }

    @Override
    public String getProcessor() {
        return processor;
    }

    @Override
    public void displayProductInfo() {
        System.out.println("Product: " + name);
        System.out.println("Price: $" + price);
        System.out.println("Brand: " + brand);
        System.out.println("Processor: " + processor);
    }
}

public class Demo {
    public static void main(String[] args) {
        // Create a DellLaptop object
        Laptop laptop = new DellLaptop("Dell XPS 13", 1299.99, "Dell", "Intel Core i7");

        // Display product information
        System.out.println("Welcome to the E-Commerce Store!");
        System.out.println("\nProduct Information:");
        laptop.displayProductInfo();
    }
}