Designing a Vending Machine in Java

Designing a Vending Machine in Java involves creating a simple program that simulates the process of selecting products, checking prices, accepting payment, and dispensing the selected item. A basic Vending Machine program typically includes elements such as products, prices, and user interactions.

Below is a basic implementation of a Vending Machine in Java that handles the selection of items, accepts payment, and returns change.

VendingMachine.java (Main Class)

import java.util.Scanner;

public class VendingMachine {
    
    // Defining products and their prices
    static String[] products = {"Soda", "Chips", "Candy", "Water"};
    static double[] prices = {1.50, 2.00, 1.00, 0.75}; 

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double userBalance = 0.0;
        int userChoice;

        // Display the available products and their prices
        displayProducts();

        // Take input from user for payment
        System.out.print("Enter money to insert (in dollars): ");
        userBalance = scanner.nextDouble();

        // Continue displaying products until user selects a valid item
        while(true) {
            // Display the products again after payment
            displayProducts();
            System.out.print("Enter the product number you want to buy (1-" + products.length + "), or 0 to exit: ");
            userChoice = scanner.nextInt();

            // If user selects 0, exit the program
            if (userChoice == 0) {
                System.out.println("Thank you for using the Vending Machine!");
                break;
            }
            
            // Check if the user entered a valid choice
            if (userChoice < 1 || userChoice > products.length) {
                System.out.println("Invalid choice, please try again.");
                continue;
            }

            // Handle purchase
            processPurchase(userChoice - 1, userBalance);
            
            // Ask user if they want to make another purchase
            System.out.print("Would you like to make another purchase? (yes/no): ");
            String continueShopping = scanner.next();
            if (!continueShopping.equalsIgnoreCase("yes")) {
                break;
            }
        }

        scanner.close();
    }

    // Method to display products and their prices
    public static void displayProducts() {
        System.out.println("\nAvailable Products:");
        for (int i = 0; i < products.length; i++) {
            System.out.println((i + 1) + ". " + products[i] + " - $" + prices[i]);
        }
    }

    // Method to process purchase
    public static void processPurchase(int productIndex, double balance) {
        double price = prices[productIndex];
        String product = products[productIndex];

        if (balance >= price) {
            double change = balance - price;
            System.out.println("\nYou have purchased " + product + " for $" + price);
            System.out.println("Your change is: $" + change);
        } else {
            System.out.println("\nInsufficient funds! Please insert more money.");
        }
    }
}

Explanation of the Program

1. Products and Prices:
   • We define an array products[] that holds the names of items in the vending machine.
   • prices[] holds the corresponding prices of the items.
2. User Input:
   • The program first asks the user how much money they want to insert.
   • It then displays the available products with their prices and prompts the user to choose an item to buy.
3. Purchase Processing:
   • The user selects an item by entering its corresponding number.
   • If the user has enough balance, the program processes the purchase, subtracts the price from the inserted money, and shows the change.
   • If the user doesn’t have enough money, it notifies them about the insufficient funds.
4. Loop for Multiple Purchases:
   • After each purchase, the program asks if the user wants to continue purchasing more items.
   • The program continues until the user decides to stop (by entering ‘no’) or exits by selecting 0.

Running the Program

Sample Output:

Available Products:
1. Soda - $1.5
2. Chips - $2.0
3. Candy - $1.0
4. Water - $0.75

Enter money to insert (in dollars): 5.0

Available Products:
1. Soda - $1.5
2. Chips - $2.0
3. Candy - $1.0
4. Water - $0.75
Enter the product number you want to buy (1-4), or 0 to exit: 1

You have purchased Soda for $1.5
Your change is: $3.5
Would you like to make another purchase? (yes/no): yes

Available Products:
1. Soda - $1.5
2. Chips - $2.0
3. Candy - $1.0
4. Water - $0.75
Enter the product number you want to buy (1-4), or 0 to exit: 2

You have purchased Chips for $2.0
Your change is: $1.5
Would you like to make another purchase? (yes/no): no
Thank you for using the Vending Machine!

Enhancements for a More Advanced Vending Machine

1. Track Inventory: You can track how many items are left for each product and decrease the count after each purchase.
2. Accepting Coins: You can create a method to accept different types of coins (quarters, dimes, nickels, etc.) rather than just a total balance.
3. Different Payment Methods: Expand the program to allow payment by credit card, digital wallets, or other payment methods.
4. Error Handling: Add error handling for invalid inputs (e.g., user enters non-numeric values).

This basic Vending Machine demonstrates how object-oriented programming can simulate a real-world process in Java. You can further enhance it by adding more complex features such as inventory management, advanced payment processing, and UI elements.