CODEWITHSUNDEEP
java
Joel
Joel

Reputation: 13

grand total using arraylist

I'm trying to learn Java, and came across a problem on one of the exercises listed in the book that I'm using. The exercise asks for me to make use of the ArrayLists to create a program that simulates a shopping cart. I've got everything up and running, however, when I try to add up the grand total finalPrice, I get a number that is way off. Any help would be great.

import java.util.ArrayList;
import java.util.Scanner;

public class Shop1 {
    public static void main(String[]args) {
        ArrayList < Item > cart = new ArrayList();

        Item item;
        String itemName;
        double itemPrice;
        int quantity;
        double finalPrice = 0;

        Scanner scan = new Scanner(System.in);

        String keepShopping = "y";

        do {
            System.out.print("Enter the name of the item: ");
            itemName = scan.next();

            System.out.print("Enter the unit price: ");
            itemPrice = scan.nextDouble();

            System.out.print("Enter the quantity: ");
            quantity = scan.nextInt();

            // create a new item and add it to the cart
            item = new Item(itemName, itemPrice, quantity);
            cart.add(item);

            for (int i = 0; i < cart.size(); i++) {
                Item temp = cart.get(i);
                System.out.println(temp);
                double subTotal =
                    ((temp.getPrice()) * (temp.getQuantity()));
                finalPrice += subTotal;

            }

            System.out.print("Continue shopping (y/n)? ");
            keepShopping = scan.next();
        } while (keepShopping.equals("y"));

        System.out.println("Please pay: $" + finalPrice);
    }
}

Upvotes: 1

Views: 3646

Answers (3)

Mike
Mike

Reputation: 2434

You're not clearing the 'finalPrice' variable before adding to it, so each time an item is added, you're starting with the 'finalPrice' from all the previous items and then adding from there.

finalPrice =0;
for (int i=0; i<cart.size(); i++)
{
    Item temp = cart.get(i);
    System.out.println(temp);
    double subTotal = ((temp.getPrice()) * (temp.getQuantity()));
    finalPrice += subTotal;
}

Since the counter 'i' isn't actually needed in this case, you can also write the code more succinctly as...

finalPrice =0;
for (Item temp: cart)
{
    System.out.println(temp);
    double subTotal = ((temp.getPrice()) * (temp.getQuantity()));
    finalPrice += subTotal;
}

But... since you're updating the final price after each item, you don't need to iterate through the entire list each time an item is added. You just need to add the price of the most recent item to the current total, so you could simply replace...

for (int i=0; i<cart.size(); i++)
{
    Item temp = cart.get(i);
    System.out.println(temp);
    double subTotal = ((temp.getPrice()) * (temp.getQuantity()));
    finalPrice += subTotal;

}

With

finalPrice += itemPrice * quantity;

Upvotes: 4

AC2MO
AC2MO

Reputation: 1637

You need to zero-out finalPrice before entering your loop, otherwise it will increase [somewhat] exponentially with each iteration. 

...
finalPrice = 0;
for (int i=0; i<cart.size(); i++)
...

Upvotes: 0

Greg Hewgill
Greg Hewgill

Reputation: 992857

It looks like you don't reset finalPrice to zero before adding up all the items in the cart. Your code will work the first time, but not if you keep shopping.

Upvotes: 0

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