Designing a Vending Machine in Java

Vending machines have become an integral part of our daily lives, offering a convenient way to access a variety of snacks and beverages. Behind their seemingly simple functionality lies a complex software design that ensures smooth user interactions and inventory management. In this section, we will walk through the process of designing a basic vending machine in Java, covering the key components and steps involved.

Understanding the Requirements

Before diving into the code, it's essential to understand the requirements of our vending machine. In this section, we will create a vending machine with the following features:

Display a list of available products.
Allow users to select a product.
Accept coins as payment (quarters, dimes, and nickels).
Calculate the total amount inserted.
Dispense the selected product and return change if necessary.
Manage product inventory.
Setting up the Project

Let's start by creating a new Java project. You can use any Integrated Development Environment (IDE) of your choice or a simple text editor and the command line. We'll call our project "VendingMachine."

Building the VendingMachine Class

The heart of our vending machine will be the VendingMachine class, which will contain methods to handle various operations. Here's a simplified version of this class:

public class VendingMachine {
    private int balance;
    private Map<String, Integer> products;
    public VendingMachine() {
        balance = 0;
        products = new HashMap<>();
    }
    public void addProduct(String product, int price, int quantity) {
        products.put(product, price * quantity);
    }
    public void insertCoin(int coinValue) {
        balance += coinValue;
    }
    public int getBalance() {
        return balance;
    }
    public void displayProducts() {
        for (Map.Entry<String, Integer> entry : products.entrySet()) {
            System.out.println(entry.getKey() + ": $" + entry.getValue() / 100.0);
        }
    }
    public void selectProduct(String product) {
        if (products.containsKey(product)) {
            int price = products.get(product);
            if (balance >= price) {
                dispenseProduct(product, price);
            } else {
                System.out.println("Please insert more coins.");
            }
        } else {
            System.out.println("Invalid product selection.");
        }
    }
    private void dispenseProduct(String product, int price) {
        System.out.println("Dispensing " + product);
        balance -= price;
        products.remove(product);
    }
}

In this class, we maintain a balance to keep track of the amount inserted by the user and a Map to store product information (name and price). The methods addProduct(), insertCoin(), getBalance(), displayProducts(), selectProduct(), and dispenseProduct() handle the various vending machine operations.

Implementation of Vending Machine

Now that we have our VendingMachine class, we can create a Main class to interact with the vending machine. Here's a simple example:

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        VendingMachine vendingMachine = new VendingMachine();
        vendingMachine.addProduct("Soda", 150, 5);
        vendingMachine.addProduct("Chips", 100, 3);
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("Welcome to the Vending Machine!");
            System.out.println("Current balance: $" + vendingMachine.getBalance() / 100.0);
            vendingMachine.displayProducts();
            System.out.print("Select a product (type 'exit' to quit): ");
            String choice = scanner.nextLine();
            if (choice.equalsIgnoreCase("exit")) {
                System.out.println("Thank you for using the Vending Machine!");
                break;
            }
            vendingMachine.selectProduct(choice);
        }
        scanner.close();
    }
}

The Main class sets up our vending machine, adds products, and allows users to interact with it through the command line.

Testing the Vending Machine

Compile and run the Main class, and we should have a simple vending machine application up and running. Users can insert coins, select products, and receive their items along with change.

File Name: VendingMachine.java

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
public class VendingMachine {
    private int balance;
    private Map<String, Integer> products;
    public VendingMachine() {
        balance = 0;
        products = new HashMap<>();
    }
    public void addProduct(String product, int price, int quantity) {
        products.put(product, price * quantity);
    }
    public void insertCoin(int coinValue) {
        balance += coinValue;
    }
    public int getBalance() {
        return balance;
    }
    public void displayProducts() {
        for (Map.Entry<String, Integer> entry : products.entrySet()) {
            System.out.println(entry.getKey() + ": $" + entry.getValue() / 100.0);
        }
    }
    public void selectProduct(String product) {
        if (products.containsKey(product)) {
            int price = products.get(product);
            if (balance >= price) {
                dispenseProduct(product, price);
            } else {
                System.out.println("Please insert more coins.");
            }
        } else {
            System.out.println("Invalid product selection.");
        }
    }
    private void dispenseProduct(String product, int price) {
        System.out.println("Dispensing " + product);
        balance -= price;
        products.remove(product);
    }
    public static void main(String[] args) {
        VendingMachine vendingMachine = new VendingMachine();
        vendingMachine.addProduct("Soda", 150, 5);
        vendingMachine.addProduct("Chips", 100, 3);
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("Welcome to the Vending Machine!");
            System.out.println("Current balance: $" + vendingMachine.getBalance() / 100.0);
            vendingMachine.displayProducts();
            System.out.print("Select a product (type 'exit' to quit): ");
            String choice = scanner.nextLine();
            if (choice.equalsIgnoreCase("exit")) {
                System.out.println("Thank you for using the Vending Machine!");
                break;
            }
            vendingMachine.selectProduct(choice);
        }
        scanner.close();
    }
}

Output:

Welcome to the Vending Machine!
Current balance: $0.0
Soda: $1.5
Chips: $1.0
Select a product (type 'exit' to quit): Soda
Dispensing Soda
Welcome to the Vending Machine!
Current balance: $0.0
Chips: $1.0
Select a product (type 'exit' to quit): Chips
Please insert more coins.
Welcome to the Vending Machine!
Current balance: $0.0
Chips: $1.0
Select a product (type 'exit' to quit): Water
Invalid product selection.
Welcome to the Vending Machine!
Current balance: $0.0
Chips: $1.0
Select a product (type 'exit' to quit): exit
Thank you for using the Vending Machine!

In this example, we can see the vending machine's functionality, including displaying available products, accepting user input, dispensing products, and handling balance and invalid selections.

Conclusion:

This section provides a basic foundation for building a vending machine in Java. We can expand upon this design by adding features like user authentication, more product options, and the ability to restock items. With some creativity and Java expertise, the possibilities are endless.

Next TopicMonolithic Applications in Java

← prev next →