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Java Java Objects Delivering the MVP Applying a Discount Code

May you assist getting a Bummer: java.lang.NullPointer Exception on java objects task 2

Where am I getting my code worng

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

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

giraffekey
giraffekey
11,650 Points

The global variable "discountCode" does not have a value when you first call the "applyDiscountCode" method in the Example class. Within the "applyDiscountCode" method, the global variable "discountCode" is being set to the return value of the "normalizeDiscountCode" method. The problem is in this method. The "normalizeDiscountCode" method uses the "discountCode" variable in its first line. However, the variable has not been declared a value yet, so the "toCharArray" method cannot be used on it since it is null, which causes an error.