Class Diagram (Mermaid)

classDiagram
    direction TB

    class Product {
        -int productId
        -String name
        -double price
        -int inventory
        +getProductId() int
        +getName() String
        +getPrice() double
        +getInventory() int
        +toString() String
    }

    class Customer {
        -int customerId
        -String name
        -String email
        -double walletBalance
        +getCustomerId() int
        +getName() String
        +getEmail() String
        +getWalletBalance() double
    }

    class CartItem {
        -int cartId
        -int customerId
        -int productId
        -String productName
        -double price
        -int quantity
        +getSubtotal() double
        +toString() String
    }

    class Bill {
        -int billId
        -int customerId
        -double totalAmount
        -Timestamp billDate
        -List~BillItem~ billItems
        +addBillItem(BillItem) void
        +getBillItems() List~BillItem~
    }

    class BillItem {
        -int billItemId
        -int billId
        -int productId
        -String productName
        -double price
        -int quantity
        -double subtotal
        +toString() String
    }

    class ProductDAO {
        +getAllProducts() List~Product~
        +getProductById(int) Product
        +reduceInventory(Connection, int, int) boolean
        +restoreInventory(Connection, int, int) boolean
    }

    class CartDAO {
        +getCartItems(int) List~CartItem~
        +getExistingQuantity(Connection, int, int) int
        +addOrUpdateCartItem(Connection, int, int, int) boolean
        +clearCart(Connection, int) boolean
    }

    class CustomerDAO {
        +getCustomerById(int) Customer
        +deductWallet(Connection, int, double) boolean
    }

    class BillDAO {
        +createBill(Connection, int, List~CartItem~, double) Bill
        +getPastOrders(int) List~Bill~
    }

    class DBConnection {
        -String URL$
        -String USER$
        -String PASSWORD$
        +getConnection()$ Connection
        +closeConnection(Connection)$ void
    }

    class ShoppingCartApp {
        -int CUSTOMER_ID$
        -ProductDAO productDAO$
        -CartDAO cartDAO$
        -CustomerDAO customerDAO$
        -BillDAO billDAO$
        +main(String[]) void$
        -addProductToCart() void$
        -checkout() void$
        -viewCart() void$
        -viewProducts() void$
        -printBill(Bill, Customer) void$
        -viewPastOrders() void$
    }

    Bill "1" *-- "many" BillItem : contains (composition)
    Customer "1" -- "many" CartItem : has
    Customer "1" -- "many" Bill : generates
    Product "1" -- "many" CartItem : referenced by
    Product "1" -- "many" BillItem : referenced by

    ProductDAO --> Product : manages
    CartDAO --> CartItem : manages
    CustomerDAO --> Customer : manages
    BillDAO --> Bill : manages
    BillDAO --> BillItem : creates

    ShoppingCartApp --> ProductDAO : uses
    ShoppingCartApp --> CartDAO : uses
    ShoppingCartApp --> CustomerDAO : uses
    ShoppingCartApp --> BillDAO : uses
    ShoppingCartApp --> DBConnection : uses

    ProductDAO --> DBConnection : uses
    CartDAO --> DBConnection : uses
    CustomerDAO --> DBConnection : uses

Loading