Java Java Objects Delivering the MVP Applying a Discount Code

Austin Miller
Austin Miller
3,142 Points

Not really sure how to check if a String has letters.

On line 24 of Order.java I'm very confused on how I can see if a String has letters in it. The previous lesson video explains how to see if a char has a specific letter in it.

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;
  }

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

  public void applyDiscountCode(String discountCode) {
    this.discountCode = normalizeDiscountCode(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

Steven Parker
Steven Parker
195,812 Points

Using the technique you know for checking a single char, you could loop through the string and check that each char in it meets the criteria.

Also, the parentheses in the "if" statement are unbalanced, the expression needs one more ")" at the end.

Austin Miller
Austin Miller
3,142 Points

I tried looping it through the String and everything seemed to work but now I'm getting an error that says "order.applyDiscountCode("h1!") and I expected it to throw an IllegalArgumentException, but it didn't". My code looks like it would do the right thing but I seem to be getting different results.

Order.java
private String normalizeDiscountCode(String discountCode) {
    char[] chars = discountCode.toCharArray();
    for (int i = 0; i <= discountCode.length(); i++) {
      if (Character.isLetter(chars[i]) || discountCode.contains("$")) {
        return discountCode = discountCode.toUpperCase();
      } else {
        throw new IllegalArgumentException("Invalid discount code");
      }
    }
    return discountCode = discountCode.toUpperCase();
  }
Steven Parker
Steven Parker
195,812 Points

The "return" should only be done after the loop finishes. Inside the loop, you only want to throw an exception if a character is bad, and keep checking the other characters if it is OK.

Also, "contains" will check the entire string. Instead, just check if the current character is a "$".

Austin Miller
Austin Miller
3,142 Points

I followed what you said and it looks like it would work but I'm still getting an error, "java.lang.IllegalArgumentException: Invalid discount code"

Order.java
private String normalizeDiscountCode(String discountCode) {
    char[] chars = discountCode.toCharArray();
    for (int i = 0; i <= discountCode.length(); i++) {
      //if the code is not a letter or a '$' then it will throw the exception
      if (! Character.isLetter(chars[i]) || chars[i] != '$') {
        throw new IllegalArgumentException("Invalid discount code");
      }
    }
    return  this.discountCode = discountCode.toUpperCase();
  }
Steven Parker
Steven Parker
195,812 Points

Very close now! I see two remaining issues:

  • the loop should stop before the index reaches the length
  • combining two "not" tests should be done with AND (&&) instead of OR (||)
Austin Miller
Austin Miller
3,142 Points

It works! Thank you for your help!