How to set discount for each position in order class

Question

I have got a program where I set price and quantity for each position in Position class. In Order class I calculate products and give discount. I have calculateDiscount method where I sum discount for all products. I would like to make discount for each position but I don't know how. I ask a some suggestion.

 package programming.com.pl;

public class Position  {

    private String name;
    private double price = 0;
    private int quantity = 0;


    public Position(String name, double price, int quantity){
        this.name = name;
        this.price = price;
        this.quantity = quantity;
    }

    public double getPrice() {
        return price;
    }

    public int getQuantity() {
        return quantity;
    }

    public String toString(){
        String str = String.format("%4s,%4s zł,%2s szt.", name,price,quantity);
        return  str;
    }
}

package programming.com.pl;

import java.util.ArrayList;

public class Order {
    final private ArrayList<Position> positions = new ArrayList<>();



    private double calculateProduct() {
        double sum = 0;
        for (Position position : positions) {
            sum = position.getPrice();
        }
        return sum;
    }

    double sumOrder() {
        double sum = 0;
        for (Position x : positions) {
            sum += calculateProduct();
        }
        return sum;
    }


    void addPosition(Position p) {
        positions.add(p);
    }

    void deletePosition(int index) {
        positions.remove(index);
    }




    double calculateDiscount() {
        double salePrice = 0;
        for (Position position : positions) {
            if (position.getQuantity() >= 5 && position.getQuantity() <= 10) {
                salePrice = calculateProduct() - (calculateProduct() * 0.05);
            } else if (position.getQuantity() <= 10 && position.getQuantity() <= 20) {
                salePrice = calculateProduct() - (calculateProduct() * 0.1);
            } else {
                salePrice = calculateProduct() - (calculateProduct() * 0.15);
            }

        }

        return salePrice;
    }
    public String toString() {
        StringBuilder sb = new StringBuilder("Order is: \n");

        for (Position p : positions) {
            sb.append(p).append("\n");
        }
        sb.append("Order sum is: ").append(sumOrder()).append("\n");
        sb.append("Discount is: ").append(calculateDiscount());
        return sb.toString();
    }
}

Answer 1

Not exactly sure what you're asking here. Are you trying to update the salePrice with a discount based on quantity? If so just update it within the relevant if loop, for example if quantity between 5 and 10 applies a 5% discount then:

salePrice = (salePrice = calculateProduct() - (calculateProduct() * 0.05)) * 0.95

If the discount is to be applied elsewhere then just set a var for each quantity case:

if (position.getQuantity() >= 5 && position.getQuantity() <= 10) {
     salePrice = calculateProduct() - (calculateProduct() * 0.05);
     discount = 0.95
}

And apply that discount to the price by multiplying, wherever necessary.