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Practice. Menu-driven "bank account" application

In current practice lesson we are going to develop a menu-driven application to manage simple bank account. It supports following operations:

deposit money;
withdraw money;
check balance.

Application is driven by a text menu.

Skeleton

First of all, let's create an application to run infinitely and ask user for a choice, until quit option is chosen:

import java.util.Scanner;

public class BankAccount {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int userChoice;

boolean quit = false;

do {

System.out.print("Your choice, 0 to quit: ");

userChoice = in.nextInt();

if (userChoice == 0)

quit = true;

} while (!quit);

}

Your choice, 0 to quit: 2

Your choice, 0 to quit: 6

Your choice, 0 to quit: 0

Bye!

Draw your attention to boolean variable quit, which is responsible for correct loop interruption. What a reason to declare additional variable, if one can check exit condition right in while statement? It's the matter of good programming style. Later you'll see why.

Bank account's functionality

It's time to add principal functionality to the program:

declare variable balance, default value 0f;
add deposit/withdraw/check balance functionality.

import java.util.Scanner;

public class BankAccount {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int userChoice;

boolean quit = false;

float balance = 0f;

do {

System.out.println("1. Deposit money");

System.out.println("2. Withdraw money");

System.out.println("3. Check balance");

System.out.print("Your choice, 0 to quit: ");

userChoice = in.nextInt();

switch (userChoice) {

case 1:

float amount;

System.out.print("Amount to deposit: ");

amount = in.nextFloat();

balance += amount;

break;

case 2:

System.out.print("Amount to withdraw: ");

amount = in.nextFloat();

balance -= amount;

break;

case 3:

System.out.println("Your balance: $" + balance);

break;

case 0:

quit = true;

break;

default:

System.out.println("Wrong choice.");

break;

}

System.out.println();

} while (!quit);

System.out.println("Bye!");

}

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 1

Amount to deposit: 100

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 2

Amount to withdraw: 50

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 3

Your balance: $50.0

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 0

Bye!

Safety checks

At the moment program allows to withdraw more than actual balance, deposit and withdraw negative amounts of money. Let's fix it, using if statement and conditions combinations.

import java.util.Scanner;

public class BankAccount {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int userChoice;

boolean quit = false;

float balance = 0f;

do {

System.out.println("1. Deposit money");

System.out.println("2. Withdraw money");

System.out.println("3. Check balance");

System.out.print("Your choice, 0 to quit: ");

userChoice = in.nextInt();

switch (userChoice) {

case 1:

float amount;

System.out.print("Amount to deposit: ");

amount = in.nextFloat();

if (amount <= 0)

System.out.println("Can't deposit nonpositive amount.");

else {

balance += amount;

System.out.println("$" + amount + " has been deposited.");

}

break;

case 2:

System.out.print("Amount to withdraw: ");

amount = in.nextFloat();

if (amount <= 0 || amount > balance)

System.out.println("Withdrawal can't be completed.");

else {

balance -= amount;

System.out.println("$" + amount + " has been withdrawn.");

}

break;

case 3:

System.out.println("Your balance: $" + balance);

break;

case 0:

quit = true;

break;

default:

System.out.println("Wrong choice.");

break;

}

System.out.println();

} while (!quit);

System.out.println("Bye!");

}

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 1

Amount to deposit: -45

Can't deposit nonpositive amount.

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 2

Amount to withdraw: 45

Withdrawal can't be completed.

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 2

Amount to withdraw: -45

Withdrawal can't be completed.

1. Deposit money

2. Withdraw money

3. Check balance

Your choice, 0 to quit: 0

Bye!

Final source

Program is complete. Below you can find final source code.

import java.util.Scanner;

public class BankAccount {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int userChoice;

boolean quit = false;

float balance = 0f;

do {

System.out.println("1. Deposit money");

System.out.println("2. Withdraw money");

System.out.println("3. Check balance");

System.out.print("Your choice, 0 to quit: ");

userChoice = in.nextInt();

switch (userChoice) {

case 1:

float amount;

System.out.print("Amount to deposit: ");

amount = in.nextFloat();

if (amount <= 0)

System.out.println("Can't deposit nonpositive amount.");

else {

balance += amount;

System.out.println("$" + amount + " has been deposited.");

}

break;

case 2:

System.out.print("Amount to withdraw: ");

amount = in.nextFloat();

if (amount <= 0 || amount > balance)

System.out.println("Withdrawal can't be completed.");

else {

balance -= amount;

System.out.println("$" + amount + " has been withdrawn.");

}

break;

case 3:

System.out.println("Your balance: $" + balance);

break;

case 0:

quit = true;

break;

default:

System.out.println("Wrong choice.");

break;

}

System.out.println();

} while (!quit);

System.out.println("Bye!");

}