java - 尝试对 ArrayList 使用 for 循环时出现 .length 错误

Question

首先，我对这个标题感到抱歉，我想不出更好的措辞方式。实际的错误在于选项 3(每当我尝试将选项 1 中的所有销售额加在一起时)。当我尝试使用 salesList.length 跟踪数组的大小时，我得到 cannot find symbol-variable length 我对使用数组列表非常陌生，并且该方法有效对我来说在早期的数组中，但该数组不是动态的。有没有特定的方法来跟踪动态数组列表的长度？

import java.util.*;
public class CustomerTest
{
public static void main(String[] args)
        {
            double totalSales = 0;
            ArrayList<String> nameList;
            nameList = new ArrayList<String>();
            ArrayList<Double> salesList;
            salesList = new ArrayList<Double>();
            Scanner myScanner = new Scanner(System.in);
            boolean done = true;     
            do
            {

                System.out.println("1) Add a new customer \n 2) Print all customers \n 3) Compute and print the total sales \n 4) Quit");
                int choice = Integer.parseInt(myScanner.nextLine());
                if (choice == 1)
                {
                    System.out.print("Add a new customer ");
                    String answer = myScanner.nextLine();
                    nameList.add(answer);
                    System.out.print("Enter their sales ");
                    String answer2 = myScanner.nextLine();
                    double answer3 = Double.parseDouble(answer2);
                    salesList.add(answer3);
                }
                else if(choice == 2)
                {
                    System.out.println("Customers: " + nameList);
                    System.out.println("Sales: " + salesList);
                }
                else if(choice == 3)
                {
                    for(int i = 0; i < salesList.length; i++)
                    {
                     totalSales = totalSales + salesList[i];   
                    } 
                    System.out.println(totalSales);
                }
                else if(choice == 4)
                {
                    System.out.println("Goodbye   *Bows gracefully*"); 
                    done = false;
                }
                else
                    System.out.println("Invalid Choice");     
            }
            while (done);
           System.exit(0);
        }
}

Answer 1

将其更改为salesList.size();。与数组不同，ArrayList 的长度不是可直接访问的字段。