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Java Java Objects Delivering the MVP Applying a Discount Code

normalizeDiscountCode => NullPointerException - why?

What is wrong here?

private String normalizeDiscountCode(String aDiscountCode) { String newString = aDiscountCode.toUpperCase(); return newString; }

I am returning the upper case version of the String aDiscountCode. Why is there an error here?

Isn't this what I am asked to do? Transform a string to upper case?

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

  public Order(String itemName, int priceInCents) {
    this.itemName = itemName;
    this.priceInCents = priceInCents;

  private String normalizeDiscountCode(String aDiscountCode) {
    String newString = aDiscountCode.toUpperCase();
    return newString; 

  public String getItemName() {
    return itemName;

  public int getPriceInCents() {
    return priceInCents;

  public String getDiscountCode() {
    return discountCode;

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

2 Answers

Hi Massimo,

The issue here seems to be the call to normalizeDiscountCode. The compiler is complaining about the parameter you are sending out of applyDiscountCode. It doesn't like the fact that the class member variable is being passed, this.discountCode. If you just pass discountCode it work fine; in terms of the exception, anyway. I'm not sure but this may be because this.discountCode is private; perhaps that means it can't be directly passed - without loading the code into Intelli-J to get more detailed error messages, I can't tell.

Back to the challenge, though. In normalizeDiscountCode for the first part of this challenge, you just want to return the received string in upper case form. We don't need to create a new string variable, but you can if you want to. Fewer lines of code would look like:

  private String normalizeDiscountCode(String aDiscountCode) {
    return aDiscountCode.toUpperCase();

Inside applyDiscountCode, assign the returned value from normalizeDiscountCode into this.discountCode. The parameter you send to normalizeDiscountCode is the same that this method receives. Don't send the member variable directly.

  public void applyDiscountCode(String discountCode) {  // <- send that one
    this.discountCode = normalizeDiscountCode(discountCode); // <- no 'this' here

I hope that makes sense.


There was a problem with the compiler as even something like this didn't work:

public String normalizeString(String aString) 
   return aString.toUpperCase();

Which works in other IDEs. After I restarted everything worked again properly.

The challenge compiler is very precise as to what it is expecting to see - entering general code in there is unlikely to work. The Preview button will show you any syntax errors but the challenge will fail if the task isn't passed.

Some of the challenges won't be 'fully loaded' so they'll only understand certain aspects of Java relating to the task in hand.

I hope you got it sorted and can move on. The next part of the challenge is frequently asked about; think your logic through about the allowed characters.

Good luck!


P.S. Shout if you need any help on any courses.