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Java Java Objects (Retired) Delivering the MVP Defaulting Parameters

So at your new Java job, you've written a brand new Shopping Cart system for the website. After some developers have...

I don't think I am getting the question. Could you please guide me to the approach to take while solving this question.. Thanks.

public class Example {

  public static void main(String[] args) {
    ShoppingCart cart = new ShoppingCart();
    Product pez = new Product("Cherry PEZ refill (12 pieces)");
    cart.addItem(pez, 5);
    /* Since a quantity of 1 is such a common argument when adding a product to the cart,
     * your fellow developers have asked you to make the following code work, as well as keeping
     * the ability to add a product and a quantity.
    Product dispenser = new Product("Yoda PEZ dispenser");
    // Uncomment this line after using method signatures to solve their request in ShoppingCart.java
    // cart.addItem(dispenser);

public class ShoppingCart {

  public void addItem(Product item, int quantity) {
    System.out.printf("Adding %d of %s to the cart.%n", quantity, item.getName());
    /* Other code omitted for clarity */
public class Product {
  /* Other code omitted for clarity, but you could imagine
     it would store price, options like size and color
  private String mName;

  public Product(String name) {
      mName = name;

  public String getName() {
      return mName;

2 Answers

Ken Alger
Ken Alger
Treehouse Teacher


I left a, rather lengthy, response to this same question on this post. Sorry for not wanting to type it all out again.

Post back if you need further explanation.

Happy coding,


Thanks Ken. Your response was very descriptive. You broke it down to such easy explanation.

Thanks again.

Here's my simplest explanation of what's going on in the 'defaulting parameters' code challenge:

Example.java has a line of code that is commented out


If all you do is uncomment this line and check your work, you get a compiler error. We need to write a second addItem method that only takes one argument, rather than two.

So, in ShoppingCart.java, we can copy and paste the existing addItem method, but remove the second argument. We also need to change what is printed, because we know that we are "Adding 1 of" of the item to the cart.