Java-覆盖父类

Question

I am new to Java and I am working on a project that works with calculating prices with/without employee discounts. After reading the following code could someone explain to me how I would need to change my code in order to get the correct output? I will explain this question in more detail at the end of the post.

Parent Class (I am NOT allowed to edit this):

public class GroceryBill {
    private Employee clerk;
    private List<Item> receipt;
    private double total;
    private double internalDiscount;

    public GroceryBill(Employee clerk) {
        this.clerk = clerk;
        receipt = new ArrayList<Item>();
        total = 0.0;
        internalDiscount = 0.0;
    }

    public void add(Item i) {
        receipt.add(i);
        total += i.getPrice();
        internalDiscount += i.getDiscount();
    }

    public double getTotal() {
        return Math.rint(total * 100) / 100.0;
    }

    public Employee getClerk() {
        return clerk;
    }

    public void printReceipt() {
        System.out.println(this);
    }

    private String valueToString(double value) {
        value = Math.rint(value * 100) / 100.0;
        String result = "" + Math.abs(value);
        if(result.indexOf(".") == result.length() - 2) {
            result += "0";
        }
        result = "$" + result;
        return result;
    }

    public String receiptToString() {
        String build = "items:\n";
        for(int i = 0; i < receipt.size(); i++) {
            build += "   " + receipt.get(i);
            if(i != receipt.size() - 1) {
                build += "\n";
            }
        }
        return build;
    }

    public String toString() {
        return receiptToString() + "\ntotal: " + valueToString(total);
    }

    public String discountToString() {
        return receiptToString() + "\nsub-total: " + valueToString(total) + "\ndiscount: " + valueToString(internalDiscount) + "\ntotal: " + valueToString(total - internalDiscount);
    }

    public static class Employee {
        private String name;

        public Employee(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }
    }

    public static class Item {
        private String name;
        private double price;
        private double discount;

        public Item(String name, double price, double discount) {
            this.name = name;
            this.price = price;
            this.discount = discount;
        }

        public double getPrice() {
            return price;
        }

        public double getDiscount() {
            return discount;
        }

        private String valueToString(double value) {
            String result = "" + Math.abs(value);
            if(result.indexOf(".") == result.length() - 2) {
                result += "0";
            }
            result = "$" + result;
            return result;
        }

        public String toString() {
            return name + " " + valueToString(price) + " (-" + valueToString(discount) + ")";
        }
    }
}

Here is my code:

public class DiscountBill extends GroceryBill
{
    private int myDiscountCount;
    private double myDiscountAmount;
    private double myPrice;
    
    public DiscountBill(Employee clerk, boolean preferred)
    {
        super(clerk);
        
        String name = "";
        double price = 0;
        double discount = 0;
        
        GroceryBill.Item myBill = new GroceryBill.Item(name, price, discount);
        myDiscountAmount = myBill.getDiscount();
        
        if (myDiscountAmount > 0 && preferred)
        {
            myDiscountCount++;
        }
    }

    public void add(Item myBill)
    {
        myPrice += myBill.getPrice();
        myDiscountAmount = myBill.getDiscount();

        if (myDiscountAmount > 0 )
        {
            myDiscountCount++;
        }
    }
    public double getTotal()
    {
        if (myDiscountCount > 0)
        {
            return myPrice - myDiscountAmount;
        }
        return myPrice;
    }
    public int getDiscountCount()
    {
        return myDiscountCount;
    }
    public double getDiscountAmount()
    {
        return myDiscountAmount;
    }
    public double getDiscountPercent()
    {
        return ((myPrice - myDiscountAmount) / myPrice * 100);
    }
}

Lastly, here is the expected output followed by my specific question:

The outputs that I am getting for my methods are one step ahead of where they should be. That is to say, my getTotal, for example, should start out as 1.35 (the first value input by the website I am using that tests my child class that I wrote) and then after another step it should be reduced to 1.1 (the website uses the employee discount using the boolean preferred from the constructor), but my program outputs 1.1 because my child class overrides the parent class's getTotal() method and never starts at the total it should (1.35). Basically I need to know how to get those original values from my parent class and THEN use the override methods to get the values after they are changed. If you want to see how this website operates, here is a link to the question I'm working on.

PS Please let me know if I need to give more/less information and ways that I can clean up this post or make it easier to understand. If my question was too broad, please ask me what you don't understand about it and I'll try my best to tell you! Thank you!

Answer 1

As far as I understood your question, what you want to do is :

Add this additional code to your DiscountBill

public class DiscountBill extends GroceryBill
{
    private static boolean isFirstTime = true;

    public double getTotal()
    {
        if (!isFirstTime && myDiscountCount > 0)
        {
           return myPrice - myDiscountAmount;
        }
        isFirstTime = false;
        return myPrice;
    }

}

Answer 2

I'm not sure if that is what you want. Do you want to call parent method? For that you can use super.parentMethodName Please correct me if I'm wrong