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Java Java Objects Delivering the MVP Applying a Discount Code

Ankit Nandi
Ankit Nandi
750 Points

nullPointerException error

The Question

For this first task, create a new private method named normalizeDiscountCode. It should take the discount code that is passed into the method and return the uppercase version. Call it from the current applyDiscountCode method and set this.discountCode to the result.


The Error

java.lang.NullPointerException (Look around Order.java line 7)

Order.java
public class Order {
  private String itemName;
  private int priceInCents;
  private String discountCode;
  private String normalizeDiscountCode(String str){

    return str.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) {
    normalizeDiscountCode(this.discountCode) ;
    this.discountCode = 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

andren
andren
28,521 Points

On the first line of your applyDiscountCode method you pass the contents of this.discountCode into the normalizeDiscountCode method. But at that point nothing has been assigned to this.discountCode, so you pass null as a value.

Therefore when toUpperCase() is called on it in the normalizeDiscountCode method, a null-pointer exception is raised.

What you should be passing into the method is actually discountCode the parameter, also you should combine your two lines into one like this:

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

That way this.discountCode will be assigned to whatever the normalizeDiscountCode returns. Which is what the instructions of the task asked you to do.

Hi Ankit,

Your normalize method is fine. However, if the applyDiscountCode method, you want to pass the parameter into normalize and assign the returned value into this.discountCode. So, applyDiscountCode receives the code as an incoming string. - pass that into the normalize method, assign the result that it returns into the member variable.

That looks like:

  private String normalizeDiscountCode(String str){
    return str.toUpperCase() ; 
  }

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

Steve.