Code for the ATM System

We've covered different aspects of the ATM and observed the attributes attached to the problem using various UML diagrams. Let's now explore the more practical side of things where we will work on implementing the ATM using multiple languages. This is usually the last step in an object-oriented design interview process.

We have chosen the following languages to write the skeleton code of the different classes present in the ATM system:

• Java

• C#

• Python

• C++

• JavaScript

ATM classes#

In this section, we will provide the skeleton code of the classes designed in the class diagram lesson.

Note: For simplicity, we are not defining getter and setter functions. The reader can assume that all class attributes are private and accessed through their respective public getter methods and modified only through their public method functions.

Enumerations #

The following code provides the definition of the enumeration used in the ATM system.

ATMState: This enumeration keeps track of the following states of an ATM:

• Idle

• Card inserted by the user

• Option selected

• Cash withdrawal

• Money transfer

• Display the account balance

Note: JavaScript does not support enumerations, so we will be using the Object.freeze() method as an alternative that freezes an object and prevents further modifications.

User and ATM card #

The User class stores the user's ATMcard and bank account, where the ATMCard class holds the card number, customer name, card expiration date, and PIN. The definitions of these classes are provided below:

Bank and bank account #

The Bank class represents a bank having a name and code and can also add an ATM. The BankAccount class represents a bank account that has two child classes: SavingAccount and CurrentAccount. These derived classes have a method for finding the withdrawal limit. The definitions of these classes are provided below:

Card reader, card dispenser, printer, screen, and keypad#

The CardReader, CashDispenser, Keypad, Screen and Printer classes compose the ATM and have the following functionalities:

• CardReader: It reads the card inserted by the user.

• CashDispenser: It dispenses cash upon withdrawal request.

• Keypad: It is used by the user to enter the PIN for authentication.

• Screen: It displays messages.

• Printer: It prints receipts.

The definitions of these classes are provided below:

ATM state#

ATMState is an abstract class that is extended by IdleState, HasCardState, SelectOperationState, CheckBalanceState, CashWithdrawalState and TransferMoneyState. All of these derived classes override the returnCard() and exit() functions of the ATMState class. The derived classes individually override the following functions:

• IdleState: This class overrides the insertCard() function.

• HasCardState: This class overrides the authenticatePin() function.

• SelectOperationState: This class overrides the selectOperation() function.

• CheckBalanceState: This class overrides the displayBalance() function.

• CashWithdrawalState: This class overrides the cashWithdrawal() function.

• TransferMoneyState: This class overrides the transferMoney() function.

The definitions of these classes are provided below:

ATM and ATM room#

An ATMRoom has an ATM and a User with the following:

• A specific state at a given moment

• Balance

• A limited number of hundred, fifty, and ten dollar bills

The definitions of these classes are provided below:

Wrapping up#

We've explored the complete design of the ATM in this chapter. We've looked at how a basic ATM system can be visualized using various UML diagrams and designed using object-oriented principles and design patterns.