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

What did I do wrong?

I don't really understand what I did wrong here Can someone please explain? It says: "Bummer: java.lang.IllegalArgumentException: Invalid discount code (Look around Order.java line 31)"

Order.java
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) { 

    for ( char letter : discountCode.toCharArray() ) {
        if ( !(Character.isLetter(letter)) || !(letter == '$') ) {
          throw new IllegalArgumentException("Invalid discount code"); 
        }
    }
    discountCode = discountCode.toUpperCase();
    return discountCode;

}
}
Example.java
public class Example {

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

    Order order = new Order(
            "Yoda PEZ Dispenser",
            600);

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

    order.applyDiscountCode("$ale");
    order.getDiscountCode(); // $ALE


    try {
      // This will throw an exception because it contains numbers
      order.applyDiscountCode("ABC123");
    } catch (IllegalArgumentException iae) {
      System.out.println(iae.getMessage());  // Prints "Invalid discount code"
    }
    try {
      // This will throw as well, because it contains a symbol.
      order.applyDiscountCode("w@w");
    }catch (IllegalArgumentException iae) {
      System.out.println(iae.getMessage());  // Prints "Invalid discount code"
    }

  }
}

1 Answer

Simon Coates
Simon Coates
8,377 Points

I think you've incorrectly applied demorgan's law. It seems to accept

private String normalizeDiscountCode(String discountCode) { 

    for (char letter : discountCode.toCharArray() ) {
        if ( !Character.isLetter(letter) && letter != '$' ) {
          throw new IllegalArgumentException("Invalid discount code."); 
        }
    }
    return discountCode.toUpperCase();
   }

A character is valid if it's a letter OR it's a $. To invert things, it becomes if not a letter AND not a $. (In honesty, a lot of people trip over this one. There are 14 pages of community questions for that challenge. I've written that code at least 10 times and I still have to think about the conditions)

Thank you!