Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Java Java Objects Delivering the MVP Applying a Discount Code

Joe Tran
Joe Tran
4,768 Points

Can't pass through the compile error

when i try to check my work, it keeps saying that a compile error happens at != in line 8, does anyone know the error?

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

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

  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) {
    try {
          this.discountCode = normalizeDiscountCode(discountCode);  
         } catch (IllegalArgumentException iae) {
                 System.out.println(iae.getMessage());
         }
   }
}
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"
    }

  }
}

2 Answers

Cam Richardson
seal-mask
MOD
.a{fill-rule:evenodd;}techdegree
Cam Richardson
Front End Web Development Treehouse Moderator 16,894 Points

The error is this:

./Order.java:8: error: incomparable types: char and String
      if (!Character.isLetter(letter) && (letter != "$")) {

Which means that you are trying to compare letter (a char) and "$" (a string). This is because in Java (and C# I believe) you must denote a character literal with single quotes like this:

char letter = 'A';

If you don't do this, the compiler will think you're meaning to define a String literal even if the string is a single character. Give it a try and let me know if that helps! :)

Joe Tran
Joe Tran
4,768 Points

Thx Richarson!

I have changed it to single quote and it compiled successfully!

However, I bumped into a new error:

Bummer: Hmmm...I ran order.applyDiscountCode("h1!") and I expected it to throw an IllegalArgumentException, but it didn't

Why cant the code throw the error in this h1! example.... any help?

Joe Tran
Joe Tran
4,768 Points

Oops, i find out the reason.

It is because the question has not asked me to catch the exception....