java为什么我输入itemName后我的程序就不能继续了？

Question

当我输入字符串“end”作为其中一项时，我不明白为什么我的程序不能继续通过while循环。我试着把println语句放在while循环之后，但在我输入“end”之后它们就不打印了。我还试着在while循环的末尾放一个print语句，但在我输入“end”后它就不打印了，所以在我输入“end”后它不会运行while循环，但在它之后它也不会运行任何东西。有什么想法吗？以下是代码：

package a1;

import java.util.Scanner;

public class A1Adept {
    public static void main(String[] args) {
           Scanner s = new Scanner(System.in);

           process(s);
    }

    public static void process(Scanner s) {

           int[] numbers = new int[10];
           double[] cost = new double[10];
           String itemName = "";
           int categoryNumb;
           int quantities;
           double costs;

           System.out.println("Please enter the names of the items, their category, their quantity, and their cost.");

           while(!itemName.equals("end")){             

               itemName = s.next();
               categoryNumb = s.nextInt();
               quantities = s.nextInt();
               costs = s.nextDouble();

               numbers[categoryNumb] += quantities;
               cost[categoryNumb] += (costs*quantities);

               }
           System.out.println("win");
           int qMax = 0;
           int qMin = 0;
           int cLarge = 0;
           int cLeast = 0;
           int max = 0;
           int min = 100;
           double large = 0;
           double least = 100;

           for (int i = 0; i < 10; i++){
               if (numbers[i] >= max)
               {
                   max = numbers[i];
                   qMax = i;
               }
               if (numbers[i] <= min){
                   min = numbers[i];
                   qMin = i;
               }
               if (cost[i] >= large){
                   large = cost[i];
                   cLarge = i;                
               }
               if (cost[i] <= least){
                   least = cost[i];
                   cLeast = i;
               }
           }

           System.out.println("Category with the most items:"+qMax);
           System.out.println("Category with the least items:"+qMin);
           System.out.println("Category with the largest cost:"+cLarge);
           System.out.println("Category with the least cost:"+cLeast);


           }

    }

Answer 1

如果你写“end”，后跟一个int，另一个int和一个double，它就会停止

这是因为您首先检查“结束”，然后请求4个输入

while（条件）在每个循环开始时进行评估

所以你的程序是这样的：

1. 检查itemName是否等于“end”
2. 询问物品名称
3. 问categoryNumb
4. 问数量
5. 询问成本
6. 做你的事
7. 回到1

如果要在用户键入“结束”后立即退出，请将其更改为：

while (true) {  // Creates an "endless" loop, will we exit from it later
  itemName = s.next();
  if (itemName.equals("end")) break; // If the user typed "end" exit the loop
  // Go on with the rest of the loop