ATM.java

// ATM.java
import java.util.*;

public class ATM {
    private HashMap<String, UserAccount> users;
    private Scanner scanner;

    public ATM() {
        users = new HashMap<>();
        scanner = new Scanner(System.in);
        seedUsers(); // Demo users
    }

    private void seedUsers() {
        users.put("himanshu", new UserAccount("himanshu", "1234", 5000));
        users.put("neha", new UserAccount("neha", "4321", 10000));
    }

    public void start() {
        System.out.println("===== Welcome to the Java ATM =====");

        int attempts = 3;
        while (attempts > 0) {
            System.out.print("Enter username: ");
            String username = scanner.nextLine();

            System.out.print("Enter PIN: ");
            String pin = scanner.nextLine();

            UserAccount user = users.get(username);
            if (user != null && user.authenticate(pin)) {
                showMenu(user);
                return;
            } else {
                attempts--;
                System.out.println("Invalid login. Attempts left: " + attempts);
            }
        }

        System.out.println("Too many failed attempts. Account blocked.");
    }

    private void showMenu(UserAccount user) {
        int choice;
        do {
            System.out.println("\nHello " + user.getUsername() + " 👋");
            System.out.println("1. Check Balance");
            System.out.println("2. Deposit Money");
            System.out.println("3. Withdraw Money");
            System.out.println("4. Transaction History");
            System.out.println("5. Change PIN");
            System.out.println("6. Exit");
            System.out.print("Choose option: ");
            choice = scanner.nextInt();

            switch (choice) {
                case 1 -> System.out.printf("Your balance is ₹%.2f\n", user.getBalance());
                case 2 -> {
                    System.out.print("Enter amount to deposit: ₹");
                    double amount = scanner.nextDouble();
                    user.deposit(amount);
                    System.out.println("Deposited successfully.");
                }
                case 3 -> {
                    System.out.print("Enter amount to withdraw: ₹");
                    double amount = scanner.nextDouble();
                    if (user.withdraw(amount)) {
                        showDenominations(amount);
                        System.out.println("Withdrawal successful.");
                    } else {
                        System.out.println("Insufficient balance.");
                    }
                }
                case 4 -> user.printTransactions();
                case 5 -> {
                    System.out.print("Enter new PIN: ");
                    scanner.nextLine(); // consume newline
                    String newPIN = scanner.nextLine();
                    user.changePIN(newPIN);
                    System.out.println("PIN changed successfully.");
                }
                case 6 -> System.out.println("Thank you for using Java ATM!");
                default -> System.out.println("Invalid option. Try again.");
            }
        } while (choice != 6);
    }

    private void showDenominations(double amount) {
        System.out.println("Dispensed as:");
        int[] notes = {2000, 500, 200, 100};
        for (int note : notes) {
            int count = (int) amount / note;
            if (count > 0) {
                System.out.println("₹" + note + " x " + count);
                amount %= note;
            }
        }
    }
}