Shopping Cart in Java: Solution, Explanation & Practice

Problem summary

Create Item and Cart classes. Cart should track items and calculate total.

Starter code

// Create Item class with name and price
// Create Cart class with:
// - addItem(Item item)
// - double getTotal()
// - int getItemCount()

public class Main {
    public static void main(String[] args) {
        // Add items and print total
        // Print: Items: <count>, Total: lt;total>
    }
}

Expected output and test cases

• 3 items totaling 45.5

  Items: 3, Total: $45.5

• Single item

  Items: 1, Total: $100.0

• Empty cart

  Items: 0, Total: $0.0

Hints

1. Use ArrayList to store items
2. Sum prices in getTotal()
3. getItemCount() returns list size

Validated solution

import java.util.ArrayList;
import java.util.List;

class Item { final double price; Item(double price) { this.price = price; } }
class Cart {
    private final List<Item> items = new ArrayList<>();
    void add(Item item) { items.add(item); }
    double total() { double total = 0; for (Item item : items) total += item.price; return total; }
    int count() { return items.size(); }
}
public class Main {
    public static void main(String[] args) {
        Cart cart = new Cart(); cart.add(new Item(10)); cart.add(new Item(15.5)); cart.add(new Item(20));
        System.out.println("Items: " + cart.count() + ", Total: quot; + cart.total());
    }
}

How to approach the problem

A Cart composes a list of Item objects and calculates its own total. The item count is derived from the collection rather than maintained as a separate, error-prone counter.

Approach

1. Represent one purchasable item.
2. Add items to the cart-owned list.
3. Derive the total by iterating over current items.

Time and space complexity

Time: O(n) for total; O(1) for add and count. Space: O(n).

Edge cases to test

• An empty cart has zero items and total zero.
• Currency rounding should be handled by BigDecimal in real checkout code.

Common mistakes

• Keeping a total field without updating it on every removal.
• Letting callers mutate the cart’s internal list.

Follow-up challenge

Add quantities and a remove-by-product operation without exposing the list.

Related OOP Basics exercises

• Practice Student Grade Calculator in Java
• Practice Bank Account Operations in Java
• Practice Circle Class in Java

Practice all OOP Basics exercises · Run this idea in the Java compiler