Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Objects Delivering the MVP Applying a Discount Code


I can't figure out how to consider if the discount code contains both letters AND the $ symbol.

public class Order {
  private String itemName;
  private int priceInCents;
  private String discountCode;

  public Order(String itemName, int priceInCents) {
    this.itemName = itemName;
    this.priceInCents = priceInCents;

  public String getItemName() {
    return itemName;

  public int getPriceInCents() {
    return priceInCents;

  public String getDiscountCode() {
    return discountCode;

  public void applyDiscountCode(String discountCode) {
    discountCode = normalizeDiscountCode(discountCode);

  private String normalizeDiscountCode(String discountCode) {
    for (char code : discountCode.toCharArray()) {
      if (!Character.isLetter(code) || discountCode.indexOf('$') != -1) {
        throw new IllegalArgumentException("Invalid discount code.");    
      } else {
        this.discountCode = discountCode.toUpperCase();
    return discountCode;
public class Example {

  public static void main(String[] args) {
    // This is here just for example use cases.

    Order order = new Order(
            "Yoda PEZ Dispenser",

    // These are valid.  They are letters and the $ character only
    order.getDiscountCode(); // ABC

    order.getDiscountCode(); // $ALE

    try {
      // This will throw an exception because it contains numbers
    } catch (IllegalArgumentException iae) {
      System.out.println(iae.getMessage());  // Prints "Invalid discount code"
    try {
      // This will throw as well, because it contains a symbol.
    }catch (IllegalArgumentException iae) {
      System.out.println(iae.getMessage());  // Prints "Invalid discount code"


2 Answers

Richard Lambert
Richard Lambert
Courses Plus Student 7,180 Points

Hello mate,

You're correctly iterating over each character of the string argument passed into normalizeDiscountCode(), but thereafter you're running into a couple of issues:

  1. Within your for loop, you have created an an else clause that calls discountCode.toUpperCase() every time a character is iterated over that satisfies this character is a letter or $. This is inefficient. The call discountCode.toUpperCase() should be made once, when you have validated that no illegal characters are present. Keep in mind also that this method is returning this validated and normalised string and not directly assigning it to the discountCode instance variable declared within the the Order class.
  2. Your logic determining whether a new IllegalArgumentException will be thrown is a little off. I approached this by stating if this character is not a letter and this character does not equal the $ symbol then throw exception.

Hope this helps


Thank you for responding. I think at one point I was really close to getting it. It took me a little bit to understand, but I got it now. Thank you for helping!!

Does this work with?

private String normalizeDiscountCode(String discountCode){ if (!discountCode.contains("[^a-zA-Z\$]+")){ throw new IllegalArgumentException("Invalid discount code."); } return discountCode.toUpperCase();