java - 如何重写java中的抽象方法？

Question

此代码的目的是查找人们希望购买的商品数量、这些商品的价格以及当前的促销情况。对于买三送一的销售，它看起来像

1 项为 5.0；折扣为0

2 项为 5.0；折扣为0

3 项为 5.0；折扣5.0

4 项为 5.0；折扣5.0

该类扩展了一个抽象类，其抽象方法是computeDiscount()

但是，我不知道如何使这个方法发挥作用，因为它不会将其视为静态，但如果该方法不是静态的，那么我不能在我的代码中使用它!

我不知道该怎么办，我迫切需要帮助

package homeFolder;

import java.util.Scanner;

public class BuyNItemsGetOneFree extends DiscountPolicy{

        static Scanner input = new Scanner(System.in);
        static double itemCost;
        static int count = count();
        static int n = getN();
        static double discount = 0;

        public static void main(String[] args) {

            itemCost = itemCost();

            for(int i = 1; i <= count; i ++) {

                discount = computeDiscount(i, itemCost);

                System.out.println(i + " items at " + itemCost +
                                    "; discount is " + discount);

            }

        }

        public static double itemCost() {

            System.out.print("Enter the cost of the item: ");
            itemCost = input.nextDouble();

            return itemCost;

        }

        public static int count() {

            System.out.print("How many items are you going to buy: ");
            count = input.nextInt();

            return count;

        }

        public static int getN() {

            System.out.print("How many items must you buy till you got one free? ");
            n = input.nextInt();

            return n;

        }

        public double computeDiscount(int count, double itemCost) {

            double discount = 0;

            if((count % n) == 0)
                discount += itemCost;

            return discount;

        }
    }

Answer 1

如果你想用 abstraction 做任何事情，你不能使用静态方法。在这里，最好使用实例变量结合工厂方法来完成所有初始化操作。

package homeFolder;

import java.util.Scanner;

public class BuyNItemsGetOneFree extends DiscountPolicy {

    // Below are your fields, or instance variables. Notice the lack of static.
    final double itemCost;
    final int count;
    final int n;

    public static void main(String[] args) {

        // Now you have an instance to work with.
        BuyNItemsGetOneFree sale = newInstance();

        for(int i = 1; i <= sale.count; i ++) {

            double discount = sale.computeDiscount(i, itemCost);

            System.out.println(i + " items at " + sale.itemCost +
                                "; discount is " + discount);

        }

    }

    // Only the factory method can access this.
    private BuyNItemsGetOneFree (double itemCost, int count, int n) {
        this.itemCost = itemCost;
        this.count = count;
        this.n = n;
    }

    public static BuyNItemsGetOneFree newInstance() {

        // The scanner really only needs to be used here.
        Scanner input = new Scanner(System.in);

        // Initilizes itemCost
        System.out.print("Enter the cost of the item: ");
        double itemCost = input.nextDouble();

        // Initilizes count
        System.out.print("How many items are you going to buy: ");
        int count = input.nextInt();

        // Initilizes n
        System.out.print("How many items must you buy till you got one free? ");
        int n = input.nextInt();

        // Constructs and returns
        return new BuyNItemsGetOneFree(itemCost, count, n);
    }

    @Override // Always add this when overriding a method.
    public double computeDiscount(int count, double itemCost) {

        double discount = 0;

        if((count % n) == 0)
            discount += itemCost;

        return discount;
    }
}

如果您想更进一步，则不需要 computeDiscount 中的参数，因为它们(据我所知)只是引用已经能够使用的字段。