public class ATM
{
    private boolean userAuthenticated;
    private int currentAccountNumber;
    private Screen screen;
    private Keypad keypad;
    private CashDispenser cashDispenser;
    private DepositSlot depositSlot;
    private BankDatabase bankDatabase;

    private static final int BALANCE_INQUIRY = 1;
    private static final int WITHDRAWAL = 2;
    private static final int DEPOSIT = 3;
    private static final int EXIT = 4;

    public ATM()
    {
        userAuthenticated = false;
        currentAccountNumber = 0;
        screen = new Screen();
        keypad = new Keypad();
        cashDispenser = new CashDispenser();
        depositSlot = new DepositSlot();
        bankDatabase = new BankDatabase();
    }

    public void run()
    {
        while(true)
        {
            while(!userAuthenticated)
            {
                screen.displayMessageLine("\nWelcome!");
                authenticateUser();
            }

            performTransactions();
            userAuthenticated=false;
            currentAccountNumber=0;
            screen.displayMessageLine("\nThank you! Goodbye!");
        }
    }

    private void authenticateUser()
    {
        screen.displayMessage("\nPlease enter your account number : ");
        int accountNumber = keypad.getInput();
        screen.displayMessage("\nEnter your PIN: ");
        int pin = keypad.getInput();

        userAuthenticated =
            bankDatabase.authenticateUser(accountNumber, pin);

        if(userAuthenticated)
        {
            currentAccountNumber = accountNumber;
        }
        else
            screen.displayMessageLine(
                "Invalid account number or PIN. Please try again");
    }

    private void performTransactions()
    {
        Transaction currentTransaction = null;

        boolean userExited = false;

        while (!userExited)
        {
            int mainMenuSelection = displayMainMenu();

            switch(mainMenuSelection)
            {
                case BALANCE_INQUIRY:
                case WITHDRAWAL:
                case DEPOSIT:

                    currentTransaction =
                        createTransaction(mainMenuSelection);

                    currentTransaction.execute();
                    break;
                case EXIT:
                    screen.displayMessageLine("\nExiting the system...");
                    userExited = true;
                    break;
                default:
                    screen.displayMessageLine(
                    "\nYou did not enter a valid selection. Try again");
                    break;
                }
            }
        }
    private int displayMainMenu()
    {
        screen.displayMessageLine("\nMain menu:");
        screen.displayMessageLine("1 - View my balance");
        screen.displayMessageLine("2 - Withdraw cash");
        screen.displayMessageLine("3 - Deposit funds");
        screen.displayMessageLine("4 - Exit\n");
        screen.displayMessage("Enter a choice : ");
        return keypad.getInput();
    }

    private Transaction createTransaction(int type)
    {
        Transaction temp = null;

        switch(type)
        {
            case BALANCE_INQUIRY:
                temp = new BalanceInquiry(
                    currentAccountNumber, screen, bankDatabase);
                    break;
            case WITHDRAWAL :
                temp = new Withdrawal(currentAccountNumber, screen,
                    bankDatabase, keypad, cashDispenser);
                    break;
            case DEPOSIT:
                temp = new Deposit (currentAccountNumber, screen,
                    bankDatabase, keypad, depositSlot);
                    break;
                }
        return temp;
    }
}