Demonstration:
This code creates a blueprint for users in a Java program. It defines a class named ‘User’
that stores information like name, student ID, username, and password. Each user has
these details kept private within the class, but methods are provided to access them
securely. When you create a new ‘User,’ you provide their information during creation,
and the class stores it. This allows you to easily manage user data in your program.
This code defines a class named ‘Item’ in Java, likely used for representing products in a
system. Here is a breakdown:
1. Class Definition:

It creates a blueprint for objects representing items (products) with specific properties
2. Attributes:




‘name’: Stores the item's name (likely a String).
‘price’: Stores the item's price (likely a double).
‘stock’: Stores the current stock level of the item (likely an integer).
These attributes are private, meaning they are only accessible within the ‘Item’ class
itself.
3. Constructor:


This special method is called when a new ‘Item’ object is created.
It takes three arguments: ‘name,’ ‘price,’ and ‘stock,’ and initializes the corresponding
attributes of the new object.
4. Getter Methods:


These methods provide controlled access to the private attributes.
‘getName(),’ ‘getPrice(),’ and ‘getStock()’ allow other parts of your code to retrieve
the item's information without directly accessing the private attributes.
5. Stock Management:



The ‘reduceStock(int quantity)’ method allows reducing the item's stock level by a
certain quantity.
It checks if there is enough stock before reduction (using an ‘if’ statement and an
‘Exception’).
If there's insufficient stock, it throws an ‘Exception’ with a message "Out of stock".
Otherwise, it subtracts the quantity from the current stock.
In essence, this code defines a reusable structure for representing items with attributes
like name, price, and stock. It also provides methods to access and manage the stock
level while ensuring there is enough stock before reduction.
This code defines a ‘Cart’ class in Java, which is likely used for managing items in a
shopping scenario. Here is a breakdown of its functionality:




The ‘Cart’ class keeps track of two things: the items themselves (‘items’) and the
corresponding quantities for each item (‘quantities’). Both are stored using lists
(‘ArrayList’).
The ‘addItem’ method allows you to add a new item (‘item’) to the cart along with the
desired quantity (‘quantity’). This method also checks if the item has enough stock
(‘reduceStock’) before adding it (assuming the ‘Item’ class has such a method).
The ‘getItems’ and ‘getQuantities’ methods provide access to the list of items and
their corresponding quantities in the cart, respectively.
The ‘getTotal’ method calculates the total price of all items in the cart. It iterates
through the items and quantities, multiplying the price of each item by its quantity,
and then sums these values to get the overall total.
In essence, this code provides a way to represent a shopping cart, keeping track of the
items and their quantities, and calculating the total price based on those details.
This code defines a ‘Shop’ class in Java, which likely represents an online or physical
store. Here is a breakdown:
Shop Class:
 This code creates a blueprint for building shop objects.
Shop Inventory:


It keeps track of available items using an ‘ArrayList’ named ‘items.’ This list stores
‘Item’ objects, which likely represent individual products in the shop.
Sample Items: The code initializes the shop with some sample items like laptops,
notebooks, and pens, each with a name, price, and quantity.
Cart Management:

The ‘Shop’ class also has a ‘Cart’ object. This suggests the shop allows customers to
add items to a virtual cart before checkout (potentially implemented in the ‘Cart’ class).
Shop Functionality:



‘getItems’ Method: This public method returns the entire list of available items (‘items’)
in the shop, allowing other parts of the code to access the product information.
‘getCart’ Method: This public method returns the ‘Cart’ object, potentially enabling
access to cart functionalities (adding/removing items, calculating total price, etc.).
‘getItem’ Method: This method takes an item name as a String and searches through
the ‘items’ list. If it finds an item with a matching name (ignoring case with
‘equalsIgnoreCase’), it returns that specific ‘Item’ object. Otherwise, it returns ‘null.’
This allows other parts of the code to retrieve details of a particular item based on its
name.
In essence, this code defines a ‘Shop’ class that manages a list of available items and
provides a cart for customer purchases. It offers methods to access the entire inventory,
individual items, and potentially interact with the cart (although cart functionality is not
shown here).
This code defines a Checkout class in Java, which is likely used in an online shopping
system. Here is a breakdown:




Class Declaration: It defines a class named Checkout. This class handles the
checkout process for a shopping cart.
Attribute: The class has a private attribute named cart of type Cart. This attribute
stores the Cart object that holds the items the user is purchasing.
Constructor: The Checkout constructor takes a Cart object as a parameter and
assigns it to the internal cart attribute. This creates a link between the Checkout and
the specific cart being checked out.
process Method: This public method is responsible for processing the checkout. Here
is what it does:
o Retrieves the total cost of all items in the cart using the cart.getTotal() method
(assuming the Cart class has this functionality).
o Prints the total cost to the user.
o Prints a thank-you message for the purchase.
In essence, this class acts like a manager for the checkout process. It takes a cart,
calculates the total, and displays the final information to the user.
This code snippet focuses on error handling during user registration. It defines four
custom exception classes that inherit from the general Exception class in Java. Each
exception class represents a specific type of validation error a user might encounter while
registering:




InvalidNameException: Thrown when the entered name contains characters other
than letters, enforcing a valid name format.
InvalidIDException: Thrown if the student ID contains non-numeric characters,
ensuring a valid ID format.
InvalidUsernameException: Thrown if the username contains spaces or other
restricted characters, promoting secure username formats.
InvalidPasswordException: Thrown if the password does not meet complexity
requirements, like lacking letters or numbers, enforcing strong password creation.
By using these custom exceptions, the code can catch specific validation errors during
registration and provide informative messages to the user. This improves the user
experience by guiding them towards valid input and preventing unexpected program
crashes due to invalid data.
This code defines the main class (UniversityShoppingSystem) for a text-based user
interface (TUI) of an online university shopping system. Here is a breakdown:
Scanner and Shop Objects:


private static Scanner scanner = new Scanner(System.in); This line creates a Scanner
object to read user input from the console.
private static Shop shop = new Shop(); This line (assuming there is a Shop class)
creates a Shop object, likely responsible for managing products, shopping carts, and
other shopping-related functionalities.
Welcome and Main Loop:


System.out.println("Welcome to the University Online Shopping System\n"); This line
greets the user upon program launch.
The while (true) loop creates an infinite loop that keeps the program running until the
user chooses to exit.
Main Menu:


Inside the loop, the code displays a menu with two options:
1. Register
2. Login
It prompts the user to enter their choice.
Choice Handling:

Based on the user's choice:
o If 1 (Register), the registerUser() method is called to handle user registration.
o If 2 (Login), the loginUser() method is called to authenticate the user and
potentially lead them to a shopping interface.
o Any other choice results in an "Invalid choice" message, prompting the user to
try again.
This code provides a basic structure for user interaction in the University Online Shopping
System. It allows users to register or login, with further functionalities likely handled within
the registerUser() and loginUser() methods (not shown here).
This code snippet defines a method called registerUser that handles the user registration
process. Here is a breakdown of what it does:
User Input and Validation:



It prompts the user to enter their name, student ID, username, and password using
System.out.print.
For each piece of information entered, it calls a corresponding validation method
(validateName, validateStudentID, etc.) to ensure the data meets specific criteria (e.g.,
name containing only letters).
If validation fails, an exception (likely one of the custom exceptions described earlier)
might be thrown, indicating the error.
User Creation and Registration:



If all validations pass, a new User object is created using the provided information
(name, studentID, etc.).
It then calls another method, registerUser(user, "users.txt"), which presumably writes
the user's details to a file named "users.txt". This is likely for storing user data
persistently.
Finally, it displays a success message upon successful registration.
Error Handling:


The entire try block encapsulates the user input, validation, and registration logic.
If any exceptions are thrown during these operations (e.g., validation error or file
writing issue), the catch block catches the exception and prints a generic error
message with the exception's message.
In essence, this code snippet collects user information, validates it to ensure data integrity,
creates a user object, stores the user data, and handles potential errors during the
registration process.
This code defines a method called `loginUser` that manages the user login process. It
prompts the user to enter their username and password. Then, it calls a separate method,
likely `loginUser(loginUsername, loginPassword, "users.txt”) `, to validate the credentials
against a user data source (potentially a file named "users.txt"). If the credentials are
valid, the user receives a success message and is directed to the shop interface through
another method call (possibly `showShopPage`). However, if the login attempt fails, the
user sees a message indicating invalid login details. Additionally, the code incorporates
error handling using a `try-catch` block. This ensures that any unexpected errors during
login, such as issues reading the user file, are caught and a generic error message is
displayed. This approach provides a user-friendly login experience with informative
feedback and safeguards against potential issues.
This code defines a method named showShopPage that presents a menu to users who
have successfully logged in. It utilizes a continuous loop (while(true)) to keep displaying
the menu until the user decides to log out. Within the loop, a menu is presented with
options like viewing products, checking their cart, initiating checkout, and logging out. The
user's choice is captured using scanner.nextLine and converted to an integer. Based on
the chosen option, the code calls relevant methods like showProducts, showCart, or
checkout. If an invalid option is entered, an error message is displayed. Notably, choosing
option 4 (logout) breaks out of the loop, ending the shop menu display and presenting a
logout message. This approach creates a user-friendly and interactive shop interface
where users can navigate through various functionalities after logging in.
Shows available products and lets you add them to your cart:
1. It lists all products with their names, prices, and stock levels.
2. You can either:
 Type the name of a product to add it to your cart.
 Type "back" to return to the shop menu.
3. If you enter a product name:
 It asks you how many of that product you want.
 It tries to find the product in the shop.
 If found, it adds the requested quantity to your cart and tells you how many were
added.
 If not found, it tells you the item is not available.
4. If you enter anything other than a product name or "back", it shows an error message.
Shows what is in your shopping cart:
1. Cart Header:
 It starts by printing a title "Cart Summary:" to let you know you are about to see
your cart contents.
2. Checking for Empty Cart:
 It retrieves the list of items and quantities in your cart from the shop object. These
are likely stored in separate lists, items, and quantities.
 It checks if the items list is empty. This means there are no items in your cart at all.
3. Displaying Cart Contents (if not empty):
 If the items list is not empty (meaning you have items in your cart):
o It uses a loop to iterate through both the items and quantities lists at the same
time. This ensures it matches the quantity with the correct item.
o Inside the loop:
– It retrieves the quantity (how many of an item) from the quantities list.
– It retrieves the item object (information about the product) from the items
list.
o It prints a line for each item in your cart, showing:
– The quantity you have (e.g., "2")
– The name of the item (e.g., "Notebook")
– The price of the item (e.g., "$50.00")
4. Empty Cart Message (if applicable):
 If the items list was empty (meaning no items in the cart), it simply prints a message
like "Cart is empty." This lets you know there is nothing to display in the cart
summary.
In essence, this code provides a detailed breakdown of your shopping cart, listing each
item and its quantity along with the price. It also considers the case where there are no
items in the cart and displays a clear message accordingly. This enhances the user
experience by offering informative feedback on the cart status.
This code snippet defines a method named checkout that initiates the checkout process
for the user's shopping cart. Here is a breakdown of what it does:
Checkout Object Creation:


It creates a new Checkout object. This object likely represents the checkout system
or logic within the shop.
It passes the user's current shopping cart (shop.getCart()) as an argument to the
Checkout constructor. This provides the checkout system with the items and
quantities the user wants to purchase.
Checkout Processing:

It calls the process() method on the newly created checkout object. This method
likely handles all the steps involved in the checkout process, such as:
o Calculating the total cost of the items in the cart.
o Handling payment processing (potentially calling other methods for credit card
details or other payment options).
o Confirming the order.
o Updating inventory levels (reducing stock based on purchased quantities).
In summary, this code creates a dedicated checkout object and delegates the entire
checkout process to that object's process() method. This promotes modularity and
separation of concerns, making the code more organized and easier to maintain.
This code defines a series of validation methods specifically designed to ensure user
input adheres to certain criteria during registration. Here is a breakdown of each method:
validateName(String name) throws InvalidNameException:



This method validates the user's name.
It throws an InvalidNameException if the name contains characters other than letters
(a-z and A-Z). This enforces names to only consist of alphabetical characters.
The throws InvalidNameException part indicates that this method can potentially
throw this exception if the validation fails.
validateStudentID(String id) throws InvalidIDException:



This method validates the user's student ID.
It throws an InvalidIDException if the ID contains characters other than numbers (09). This ensures student IDs only consist of numeric digits.
Like the validateName method, it throws an exception if validation fails.
validateUsername(String username) throws InvalidUsernameException:


This method validates the user's username.
It throws an InvalidUsernameException if the username contains spaces. This
prevents usernames from having spaces, potentially improving readability, and
avoiding conflicts.
validatePassword(String password) throws InvalidPasswordException:


This method validates the user's password.
It throws an InvalidPasswordException if the password does not meet certain
criteria. The specific criteria are defined by the regular expression ^(?=.*[09])(?=.*[a-zA-Z]).+$. This regex likely enforces passwords to contain both letters and
numbers, potentially improving security.
In essence, these methods act as checkpoints during user registration, ensuring data
entered adheres to specific rules. If any validation fails, the corresponding exception is
thrown, which can be caught and handled elsewhere in the code to provide informative
error messages to the user. This approach helps prevent invalid data from entering the
system and improves the overall user experience during registration.
This code snippet defines two methods for user management:
RegisterUser(User user, String filename) throws IOException:



This method registers a new user in the system.
It takes two arguments:
o User user: This object likely contains the user's information like name, student
ID, username, and password.
o String filename: This specifies the filename where user data will be stored
(potentially a text file).
It uses a try-with-resources statement to manage a FileWriter object automatically.
This object writes data to the specified file.
o Inside the try block:
– It writes each piece of user information (name, student ID, username,
password) to the file on separate lines.
–

It adds an extra blank line after each user's information for better readability
and separation in the file.
The throws IOException part indicates this method can potentially throw an
IOException if there are issues writing to the file (e.g., file not found, permission
issues).
LoginUser(String username, String password, String filename) throws IOException:





This method attempts to log in a user with the provided credentials.
It takes three arguments:
o String username: The username entered by the user during login.
o String password: The password entered by the user during login.
o String filename: This specifies the filename containing user data (same file used
for registration).
It uses a try-with-resources statement to manage a BufferedReader object
automatically. This object reads data from the specified file line by line.
o Inside the try block:
– It reads lines from the file one by one using a while loop.
– It checks if the current line read from the file matches the provided
username.
o If the username matches:
 It reads the next line, assuming it stores the password for that
user.
 It compares the stored password with the password entered by
the user.
 If both usernames and passwords match, the method returns
true, indicating a successful login.
– If the username does not match or the passwords do not match, the loop
continues reading the file.
The throws IOException part indicates this method can potentially throw an
IOException if there are issues reading from the file.
If no matching username is found in the file or the passwords do not match, the method
returns false, indicating a failed login attempt.
In summary, these methods provide functionalities for registering new users and logging
in existing users using a text file for data storage. The code uses exception handling to
gracefully handle potential file access issues.