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!

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 don't understand what's wrog with my code ?

I've seen that other people are solving the problem with a For Statement and I don't understand why and I don't understand a lot of what it says in their code like this one: for(i=0; i<discountCode.length(); i++){ char ch = discountCode.charAt(i); if (! (Character.isLetter(ch)) || ch == '$')){ // double ' ) ' throw new IllegalArgumentException("Invalid discount code") I mean I could just copy this and that's it, but I want to understand why am I understanding a different instruction or what am I not understanding. Could somebody help me with this ?

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) {
    this.discountCode = normalizeDiscountCode (discountCode);

    private String normalizeDiscountCode (String discountCode) {
      if (! Character.isLetter  (letter | $)) {
      throw new IllegalArgumentException("Invalid discount code");
    return discountCode.toUpperCase();
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"


1 Answer

normalizeDiscountCode method is not implemented in a right way

  private String normalizeDiscountCode(String discountCode){
    for(char letter: discountCode.toCharArray()){
        if(!Character.isLetter(letter) && letter != 36){
         throw new IllegalArgumentException("Invalid discount code.");
    return discountCode.toUpperCase();      

if you need more help, please post here in the Community :)