Question

我试图调试它，但我不知道我丢失了什么代码。介意检查我？我想将项目名称，价格和数量添加到ITEM[]数组中，但是当我尝试打印时，它不会返回任何内容

item.java

import java.text.NumberFormat;

public class Item {
    private String name;
    private double price;
    private int quantity;

    public Item(String itemName, double itemPrice, int numPurchased) {
        name = itemName;
        price = itemPrice;
        quantity = numPurchased;
    }

    public String toString() {
        NumberFormat fmt = NumberFormat.getCurrencyInstance();
        return (name + "\t" + fmt.format(price) + "\t" + quantity + "\t"
                + fmt.format(price * quantity));
    }

    public double getPrice() {
        return price;
    }

    public String getName() {
        return name;
    }

    public int getQuantity() {
        return quantity;
    }

}

ShoppingCart.java

import java.text.NumberFormat;
public class ShoppingCart {
private int itemCount; // total number of items in the cart
private double totalPrice; // total price of items in the cart
private int capacity; // current cart capacity
private Item[] cart = new Item[capacity];

// -----------------------------------------------------------
// Creates an empty shopping cart with a capacity of 5 items.
// -----------------------------------------------------------
public ShoppingCart()
{
capacity = 5;
itemCount = 0;
totalPrice = 0.0;
}

// -------------------------------------------------------
// Adds an item to the shopping cart.
// -------------------------------------------------------
public void addToCart(String itemName, double price, int quantity)
{if(itemCount==cart.length)
 increaseSize();
else{
cart[itemCount]=new Item(itemName, price, quantity);
totalPrice += (totalPrice * quantity);
itemCount++;
}
}
// -------------------------------------------------------
// Returns the contents of the cart together with
// summary information.
// -------------------------------------------------------

public String toString()
{
NumberFormat fmt = NumberFormat.getCurrencyInstance();
String contents = "\nShopping Cart\n";
contents += "\nItem\t\tUnit Price\tQuantity\tTotal\n";
for (int i = 0; i < itemCount; i++)
contents += cart[i].toString() + "\n";
contents += "\nTotal Price: " + fmt.format(totalPrice);
contents += "\n";
return contents;
 }
// ---------------------------------------------------------
// Increases the capacity of the shopping cart by 3
// ---------------------------------------------------------
private void increaseSize()
{Item[] temp = new Item[cart.length + 3];
for (int num = 0; num < cart.length; num++)
{
temp[num] = cart[num];
cart = temp;

}

}



}

Shopping1.java

import java.util.Scanner;
public class Shopping1 {


 public static void main(String[] args)
{
 String answer="y";
 ShoppingCart cart = new ShoppingCart();
 while(answer=="y")
 {
 System.out.println("Enter the Name, Price, and Quantity of Item:");
 Scanner scan = new Scanner (System.in);
 String name = scan.next();
 double price = scan.nextDouble();
 int quantity = scan.nextInt();

 cart.addToCart(name, price, quantity);

 String printout = cart.toString();
 System.out.println(printout);
 System.out.println("Do you want to continue? y/n");
 Scanner ans = new Scanner (System.in);
 answer = ans.next();
 }
 System.out.println("thank you !");
}
}

我的输出是：

输入物品的名称，价格和数量：   yuvin
  3
  2

Shopping Cart

Item        Unit Price  Quantity    Total

Total Price: MYR0.00

你想继续吗？ Y / N
  ñ
  谢谢！

虽然我期待一些我刚刚插入的数组的返回

Answer 1

此行中totalPrice始终为0：

totalPrice += (totalPrice * quantity);

我想你想要：

totalPrice + =（price * quantity）;

Answer 2

行

private Item[] cart = new Item[capacity];

在构造函数之前执行，因此当时容量将为零，并且您将获得一个没有元素空间的数组...

//编辑：

此外，addToCart方法存在缺陷......

if（itemCount == cart.length）为true，您要添加的项目将被丢弃，因为您只增加了数组大小...您应该增加数组大小然后添加项目... < / p>

Answer 3

当您实例化购物车时：

private Item[] cart = new Item[capacity];

容量为空。（设置 NullPointerException ）。当你去实例化它时，你需要确保容量除了null之外还有某种类型的值。如何将购物车的尺寸设为0，因此您无法实际添加任何内容。

考虑使用ArrayList，因此大小是动态的？

Answer 4

您应该单独测试每个方法，并确保它符合您的预期，而不是尝试将程序调试为单个质量。例如，这种方法：

private void increaseSize()
{
    Item[] temp = new Item[cart.length + 3];
    for (int num = 0; num < cart.length; num++)
    {
        temp[num] = cart[num];
        cart = temp;
    }
}

没有做你想做的事情：它会增加cart的大小，是的，但它也会将cart的每个元素设置为null，{{1}除外}。如果你测试过这种方法，你会看到这个问题。

我的数组没有返回任何内容。对于shopping1.java

4 个答案: