将数组中对象的值相加

Question

我正在尝试在我的方法 getTotalCost 中将所有成本值和数量值相加，并将它们从我的数组对象 list[i] 相乘（如代码所示）：

public class GroceryList {
    private int i;

    GroceryItemOrder list[] = new GroceryItemOrder[10];

    public void addItem(String name, double cost, int quantity) {
        try {
            for (i = 0; i < list.length; i++) {
                list[i] = new GroceryItemOrder(name, cost, quantity);

                if (list[i] == list[9] && list[i] != null) {
                    System.out.format("%6s %-15S %10gKR. %4d stk.%n", "",
                            list[i].getName_Food(),
                            list[i].getCost_Food(),
                            list[i].getQuantity_Food()
                    );
                }
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("You put too many groceries in your cart!");
            System.exit(0);
        }
    }

    public void getTotalCost(){
        System.out.println();

        try {
            double totalAmount;
            totalAmount = list[i].getCost_Food() * list[i].getQuantity_Food();
            System.out.println("The Total Amount is: " + totalAmount);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Something went wrong");
        }
    }
}

this below is my main class:    

package com.company;

public class Main {

public static void main(String[] args) {

    GroceryList gL = new GroceryList();

    receipt();

    gL.addItem("Bananer",10,6);
    gL.addItem("Toiletpapir",40,2);
    gL.addItem("Svinekød",30,1);
    gL.addItem("Papir",25,1);
    gL.addItem("Sødmælk",10,3);
    gL.addItem("Færdigret",15,5);

    //=130
    /*
    gL.addItem("Kylling",10,2);
    gL.addItem("Kaffe",10,2);
    gL.addItem("Bønner",10,2);
    gL.addItem("Kage",10,2);
    //*/

    gL.getTotalCost();


}

public static void receipt(){
    System.out.println("");
    System.out.printf("%9S %1S%n","","\"~discount supermarket receipt~\"");
    System.out.printf("%15S %15S %15S%n","Grocery:","Cost:","Quantity:");
    System.out.println("");
}

}

这是我现在在删除 try/catch 时遇到的输出错误：

线程“main”中的异常 java.lang.ArrayIndexOutOfBoundsException: 10 在 com.company.GroceryList.getTotalCost(GroceryList.java:33) 在 com.company.Main.main(Main.java:26)

我想得到：

总金额为：xxx

Answer 1

您必须跟踪添加到数组中的项目数。
所以在类级别声明这个变量，而不是i：

private int counter = 0;

您的 addItem() 方法包含一个 for 循环。为什么？
这个方法应该给list增加1项，所以改成这样：

public void addItem(String name, double cost, int quantity) {
    if (counter == list.length) {
        System.out.println("Your cart is full! No more items can be added.");
        return;
    }
    list[counter] = new GroceryItemOrder(name, cost, quantity);
    counter++;
}

现在在getTotalCost() 中，您确实需要一个for 循环来遍历列表中的所有项目并获得您需要的总数：

public void getTotalCost(){
    double totalAmount = 0.0;
    System.out.println();
    for (int i = 0; i < counter; i++) {
        totalAmount += list[i].getCost_Food() * list[i].getQuantity_Food();
        System.out.format("%6s %-15S %10gKR. %4d stk.%n", "",
                        list[i].getName_Food(),
                        list[i].getCost_Food(),
                        list[i].getQuantity_Food()
        );
    }
    System.out.println("The Total Amount is: " + totalAmount);
}