Question

我正在使用toString()方法编写一个子类，当在数组列表中读取该子类的项时，我希望将其打印出来，但是当该类型的项目将添加到arraylist。这是子类的代码：

toString()

这是超类package shop; import java.text.DecimalFormat; public class MultiBuyProduct extends Product{ private int minDiscountedQuantity; private int discountPercent; public MultiBuyProduct(String name, double price, int quantity, int minDiscountedQuantity, int discountPercent) { super(name, price, quantity); this.minDiscountedQuantity = minDiscountedQuantity; this.discountPercent = discountPercent; } //getters and setters public double getTotalPrice() { if (getQuantity() >= getMinDiscountedQuantity()) { double total = getPrice() * getQuantity(); double discountedTotal = total - ((discountPercent/100) * total); return discountedTotal; } return getPrice() * getQuantity(); } public double discount() { double total = getPrice() * getQuantity(); double discount = (discountPercent/100) * total; return discount; } @Override public String toString() { DecimalFormat format = new DecimalFormat("#.00"); return String.format("%s,\n%20s%5.2f)", super.toString(), format.format(getTotalPrice()), "(Multibuy Discount: GBP ", discount()); } }

中的toString

Products

我在这里是包含主要方法public String toString() { DecimalFormat format = new DecimalFormat("#.00"); return String.format("%3d * GBP %5s %-20s= GBP %7s", quantity, format.format(price), name, format.format(getTotalPrice())); }的类的一部分：

ShoppingCart

打印：

public class ShoppingCart {
private ArrayList<Product> cart;

    public ShoppingCart() {
        cart = new ArrayList<>();
    }
    @Override
    public String toString() {
        double total = 0;
        StringBuilder sb = new StringBuilder();
        for (Product p : cart) {
            sb.append(p.toString()).append("\n");
            total += p.getTotalPrice();
        }
        sb.append(String.format("%48s \n%40s%8.2f", "------------", "TOTAL GBP", total));
        return sb.toString();
    }

    public static void main(String[] args) {
        ShoppingCart newCart = new ShoppingCart();

        Product apple, milk, caulk, ice, snakes;
        MultiBuyProduct snakesMulti;
        apple = new Product("Apples (4 pack)", 1.20, 1);
        milk = new Product("Milk (1l)", 0.75, 1);
        caulk = new Product("Caulk (1l)", 6.84, 1);
        ice = new Product("Ice (1kg)", 4.30, 1);
        snakes = new Product("Snake (5m)", 32.0, 1);
        snakesMulti = new MultiBuyProduct("Snakes", 30.0, 12, 3, 20);

        newCart.add(apple);
        newCart.add(apple);
        newCart.add(apple);
        newCart.add(caulk);
        newCart.add(milk);
        newCart.add(milk);
        newCart.add(snakes);
        newCart.add(ice);
        newCart.add(ice);
        newCart.add(snakesMulti);


        System.out.println(newCart);


    }

但它应该打印：

  3 * GBP  1.20  Apples (4 pack)     = GBP    3.60
  1 * GBP  6.84  Caulk (1l)          = GBP    6.84
  2 * GBP   .75  Milk (1l)           = GBP    1.50
  1 * GBP 32.00  Snake (5m)          = GBP   32.00
  2 * GBP  4.30  Ice (1kg)           = GBP    8.60
 12 * GBP 30.00  Snakes              = GBP  360.00
                                    ------------ 
                               TOTAL GBP  412.54

我是否需要3 * GBP 1.20 Apples (4 pack) = GBP 3.60 1 * GBP 6.84 Caulk (1l) = GBP 6.84 2 * GBP .75 Milk (1l) = GBP 1.50 1 * GBP 32.00 Snake (5m) = GBP 32.00 2 * GBP 4.30 Ice (1kg) = GBP 8.60 12 * GBP 30.00 Snakes = GBP 288.00 (Multibuy Discount: GBP 72.00 ------------ TOTAL GBP 340.54本身的主要方法，还是可以使用MultiBuyProduct中的主要方法？如果需要，我可以为上下文提供更多代码。

编辑：我已经找到问题的根源。在ShoppingCart中，我检查该项目，如果它不在arraylist中，它将创建该项目的副本并将其添加到arraylist中：

ShoppingCart.add()

public void add(Product p) { if (cart.size() > 0) { for (Product i : cart) { if (i.getName().equals(p.getName()) && i.getPrice() == p.getPrice()) { i.setQuantity(i.getQuantity() + p.getQuantity()); return; } } cart.add(new Product(p)); //this is done because if it were just cart.add(p), it would change the product being assigned as well as the product in the arraylist } else { cart.add(new Product(p)); } }在Product (p)中定义为

Product

这意味着public Product(Product p) { this.name = p.name; this.price = p.price; this.quantity = p.quantity; }类型的所有项目都会丢失其MultiBuyProduct和minDiscountedQuantity的值。我不确定如何解决此问题，因为我无法将discountPercent扩展到public Product(Product p)

Answer 1

这是一些示例代码。请查看这是否是您的应用程序试图执行的操作（这是行为）吗？

该示例具有Animal类。 Dog类扩展了 Animal。两者都覆盖了java.lang.Object的{{1}}方法。

toString

输出：

class Animal {

    private String name;

    public Animal(String s) {
        name = s;
    }

    public String toString() {
        return "Animal name: " + name;
    }
}

class Dog extends Animal {

    private String name;

    public Dog(String s) {
        super(s);
        name = s;
    }

    public String toString() {
        return "Dog Name: " + name + ", " + super.toString();
    }
}


Public class TestingInheritance {
    public static void main(String [] args) {

        Animal d0 = new Animal("just animal");  
        Animal d1 = new Dog("mutt");
        Dog d2 = new Dog("pup");

        System.out.println(d0);
        System.out.println(d1);
        System.out.println(d2);
        System.out.println("");

        List<Animal>  anims = Arrays.asList(d0, d1, d2);
        for (Animal a : anims) {
            System.out.println(a.toString());
        }
    }
}

为什么我的toString（）方法没有正确覆盖其超类中的toString（）方法？

1 个答案: