How to verify a specific character?

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 code, char ignore) {

                              for (char ch: code.toCharArray()){ 
                                if  ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))  {

                                discountCode= code.toUpperCase();
                              } 

                              else {
                              throw new IllegalArgumentException("Invalid discoubt code");  
                              }
                              }
                              return discountCode;  
                              }

public String getItemName() {
return itemName;
}

public int getPriceInCents() {
return priceInCents;
}

public String getDiscountCode() {
return discountCode;
}

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

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"
    }

  }
}