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Java Java Objects Delivering the MVP Applying a Discount Code

Ray Green
Ray Green
4,690 Points
Posted by Ray Green
Ray Green
4,690 Points

illegalArgumentExceptions

Is my code incorrect or is the treehouse code challenge thing malfunctioning? When i run this the compiler literally prints my IllegalArgumentException which is the whole purpose of the challenge but its getting passed as incorrect.

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"
    }

  }
}

2 Answers

Yanuar Prakoso
Yanuar Prakoso
15,196 Points
Yanuar Prakoso
Yanuar Prakoso
15,196 Points

Hi Ray

You almost finish the challenge. You just make a small mistake here:

for(char letter : discountCode.toCharArray()){
      if (! Character.isLetter(letter) || letter != '$'){ <-- this part is wrong
      throw new IllegalArgumentException("Invalid discount code.");
      }
    }

the challenge said if the discountCode characters is NOT(a letter OR '$') then throw new IllegalArgumentException. Thus you should write the code as if(!(Character.isLetter(letter) || leter == '$')) like this:

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

or if you still want to use negation for each statement, you must transform it into: if(!Character.isLetter(letter) && letter != '$') like this: 

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

This is what is known as De Morgan's Law, you can read more about it here

I hope this can help a little

Jennifer Nordell
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STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there! You're doing great, but the logic in your character comparison is a bit off. You're saying if it's not a letter or it's not a dollar sign then throw an exception. So, for instance, if I sent in the letter "h" here, it would throw an exception, because it's not equal to the dollar sign. Remember, with an or, || only one must be true for the following block to execute. And since "h" is not equal to a dollar sign, the exception will be thrown.

What we want here is the neither/nor logic and this needs an and with &&. We're saying if it's not a letter and it's not a dollar sign, then throw the exception.

Long story short, switching out your || for && causes this to pass.

Hope this helps! :sparkles: