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API Reference - Library Management System

Overview

This document provides a quick reference for all methods, data structures, and usage patterns in the Library Management System.

Table of Contents

Core Methods

Authentication Methods

register()

public static void register()

Description: Handles user registration with interactive input.

Behavior:

  • Prompts for username and password via console
  • Validates username uniqueness
  • Loops until valid unique username is provided
  • Stores credentials in registeredAcc

Side Effects: Modifies global registeredAcc hashtable

Example Flow:

Input: username = "newuser", password = "mypass"
Result: registeredAcc.put("newuser", "mypass")

checkAccount(String username, String password)

public static String checkAccount(String username, String password)

Description: Validates user login credentials.

Parameters:

Parameter Type Description
username String User's login identifier
password String User's password

Returns:

Return Value Description
null Valid credentials
"Username doesn't exist!" Username not found
"Wrong password!" Invalid password

Example:

// Valid login
String result = checkAccount("carlo", "morva");
// result = null

// Invalid username
String result = checkAccount("nonexistent", "password");
// result = "Username doesn't exist!"

// Wrong password
String result = checkAccount("carlo", "wrongpass");
// result = "Wrong password!"

Borrowing Management

borrowersHandler(String username)

public static boolean borrowersHandler(String username)

Description: Checks if a user has any borrowed books.

Parameters:

Parameter Type Description
username String Username to check

Returns:

Return Value Description
true User has borrowed books
false User has no borrowed books

Algorithm:

  1. Iterates through borrowers TreeMap keys
  2. Splits each key by comma: "username, date, (count)"
  3. Checks if any key contains the target username

Example:

// Assuming borrowers contains: "john, 2024-01-15, (1)" → "Java Book"
boolean hasBorrowed = borrowersHandler("john");
// hasBorrowed = true

boolean hasBorrowed = borrowersHandler("mary");
// hasBorrowed = false (if mary has no borrowed books)

Data Structures

registeredAcc: Hashtable<String, String>

Purpose: Store user account credentials

Structure:

Key (Username) → Value (Password)
"carlo" → "morva"
"john" → "password123"

Operations:

// Add user
registeredAcc.put(username, password);

// Check user exists
if (registeredAcc.get(username) != null) { }

// Validate password
if (password.equals(registeredAcc.get(username))) { }

borrowers: TreeMap<String, String>

Purpose: Track borrowed books with timestamps and borrowing counts

Key Format: "username, date, (borrowCount)" Value: Book title

Structure:

Key → Value
"john, 2024-01-15, (1)" → "Java Programming"
"john, 2024-01-15, (2)" → "Web Development"
"mary, 2024-01-16, (1)" → "Data Structures"

Key Components:

  1. Username: Borrower's username
  2. Date: Borrowing date (LocalDate format)
  3. Count: Sequential borrowing number (1 or 2)

Operations:

// Add borrowed book
borrowers.put(username + ", " + date + ", " + "(" + borrowCount + ")", bookName);

// Find user's borrowed books
for (String key : borrowers.keySet()) {
    if (key.contains(username)) {
        String borrowedBook = borrowers.get(key);
    }
}

// Remove returned book
borrowers.remove(key);

books: Hashtable<String, String>

Purpose: Store available books with their access links

Structure:

Key (Book Title) → Value (Book Link)
"Java" → "https://pdfdrive.com/Java"
"JavaScript" → "https://pdfdrive.com/JavaScript"

Operations:

// Add book
books.put(bookTitle, bookLink);

// Remove book
books.remove(bookTitle);

// Check book exists
if (books.get(bookTitle) != null) { }

// Get book link
String link = books.get(bookTitle);

// List all books
for (String title : books.keySet()) {
    System.out.println(title + " - " + books.get(title));
}

suggestedBooks: HashSet<String>

Purpose: Store unique book suggestions from users

Structure:

Set of book titles (duplicates automatically removed)
{"Advanced Java", "Python Basics", "Database Design"}

Operations:

// Add suggestion
suggestedBooks.add(bookTitle);

// Check if suggestion exists
if (suggestedBooks.contains(bookTitle)) { }

// Remove suggestion (when added to library)
suggestedBooks.remove(bookTitle);

// List all suggestions
for (String suggestion : suggestedBooks) {
    System.out.println(suggestion);
}

Usage Examples

Complete User Registration Flow

// 1. User chooses to register
System.out.print("Do you have an account?[y/n]: ");
String response = input.nextLine(); // "n"

// 2. Registration process
if (response.equals("n")) {
    register(); // Handles input and validation
}

Complete Login and Access Flow

// 1. User provides credentials
System.out.print("Enter username: ");
String username = input.nextLine();
System.out.print("Enter password: ");
String password = input.nextLine();

// 2. Validate credentials
String validation = checkAccount(username, password);

// 3. Route based on validation and role
if (validation == null) {
    if (username.equals("carlo") && password.equals("morva")) {
        // Admin access
        handleAdminDashboard();
    } else {
        // Guest access
        handleGuestDashboard();
    }
} else {
    System.out.println(validation); // Error message
}

Book Borrowing Flow

// 1. Check borrowing eligibility
if (borrowCount < 2) {
    // 2. Display available books
    for (String book : books.keySet()) {
        System.out.println(book);
    }
    
    // 3. User selects book
    String selectedBook = input.nextLine();
    
    // 4. Validate book exists
    if (books.get(selectedBook) != null) {
        // 5. Update borrowing records
        borrowCount++;
        String key = username + ", " + date + ", (" + borrowCount + ")";
        borrowers.put(key, selectedBook);
    }
}

Constants and Configuration

Default Accounts

// Admin account
Username: "carlo"
Password: "morva"

// Pre-registered guest accounts
"carlo2" → "morva2"
"carlo3" → "morva3"
"carlo32" → "morva"

Initial Books

"Java" → "https://pdfdrive.com/Java"
"JavaScript" → "https://pdfdrive.com/JavaScript"

System Limits

MAX_BORROW_LIMIT = 2;           // Maximum books per user
BORROW_DURATION_DAYS = 30;      // Maximum borrowing period

Menu Options

// Admin menu
String[] adminCommands = {
    "Add a new book",
    "Remove a book", 
    "See list of borrowers",
    "View suggestions",
    "Log-out"
};

// Guest menu
String[] guestCommands = {
    "Browse a book",
    "Borrow a book",
    "Return a book",
    "Suggest a book",
    "Log-out"
};

Error Codes

Authentication Errors

Error Message Cause Solution
"Username already taken!" Registration with existing username Choose different username
"Username doesn't exist!" Login with non-existent username Register first or check spelling
"Wrong password!" Incorrect password Enter correct password

Borrowing Errors

Error Message Cause Solution
"You already borrowed 2 books!" Borrowing limit reached Return a book first
"You already borrowed this book!" Duplicate borrowing attempt Choose different book
"No book found!" Invalid book title Check available books list
"You have not borrowed any books." Return attempt with no borrowed books Borrow books first

System Messages

Message Context Meaning
"No books available at the moment" Empty library Admin needs to add books
"No guests borrowed for a moment.." Empty borrowers list No current borrowers
"No user-suggestions at the moment..." Empty suggestions No pending suggestions

State Management

Global State Variables

static Hashtable<String, String> registeredAcc = new Hashtable<>();
static TreeMap<String, String> borrowers = new TreeMap<String, String>();
static Hashtable<String, String> books = new Hashtable<>();
static Set<String> keys = registeredAcc.keySet();

Session Variables (Local to main)

LocalDate date = LocalDate.now();                    // Current date
HashSet<String> suggestedBooks = new HashSet<>();    // User suggestions
ArrayList<String> borrowCountHistory = new ArrayList<>(); // Borrow count tracking
int borrowCount = 0;                                  // Current user's borrow count

State Transitions

Application Start → User Choice (y/n for account)
    ↓
Registration/Login → Credential Validation
    ↓
Role Detection → Admin Dashboard / Guest Dashboard
    ↓
Menu Selection → Feature Execution → Back to Menu
    ↓
Logout → Back to Main Menu

Version: 1.0
Last Updated: [Current Date]
Compatible with: Java 8+