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!");
         }
     }

     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);
         userAuthenticated = bankDatabase.authenticateUser(accountNumber, pin);
         if(userAuthenticated){
             currentAccountNumber = accountNumber;
         }
         else{
             screen.displayMessageLine("Invalid Account Number or PIN.");
             screen.displayMessageLine("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.");
                     screen.displayMessageLine("Please 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;
     }
}