如何修复我的 NoSuchElementException？

Question

我尝试了很多不同的方法来修复错误。我知道它与hasNext有关，我只是不确定错误在哪里。请帮忙。另外，如果有人能告诉我如何从我的 getLargestQuantityItem 方法中将变量 largestQuantity 的值获取到 main 方法中，我将不胜感激。干杯！

这是一个 .txt 文件的输入文件：

The Shawshank Redemption
100
19.95
DVD
The Dark Knight
50
19.95
DVD
Casablanca
137
9.95
DVD
The Girl With The Dragon Tattoo
150
14.95
Book
Vertigo
55
9.95
DVD
A Game of Thrones
100
8.95
Book

这是我的代码：

import java.util.*;
import java.io.*;

public class Project01 {

public static void main(String[] args) {
    ArrayList<String> Titles = new ArrayList<String>();
    ArrayList<String> Types = new ArrayList<String>();
    ArrayList<Double> Prices = new ArrayList<Double>();
    ArrayList<Integer> Quantities = new ArrayList<Integer>();
    int count = 0;
    Scanner in = new Scanner(System.in);
    String database = getFile(in);
    try {
        File file = new File(database);
        Scanner inputFile = new Scanner(file);
        System.out.println();
        System.out.println("Product Summary Report");
        System.out.println("------------------------------------------------------------");
        while (inputFile.hasNext()) {
            getTitle(Titles, inputFile.nextLine());
            getQuantity(Quantities, inputFile.nextInt());
            getPrice(Prices, inputFile.nextDouble());
            getType(Types, inputFile.next());
            System.out.println("Title: " + Titles.get(count));
            System.out.println(" Product Type: " + Types.get(count));
            System.out.println(" Price: " + Prices.get(count));
            System.out.println(" Quantity: " + Quantities.get(count));
            System.out.println();
            count++;
            inputFile.next();
        }
        System.out.println("-----------------------------------------------------------------");
        System.out.println("Total products in database: " + count);
        System.out.println("Largest quantity item: " + largestQuantity);
        System.out.println("Highest total dollar item: ");
        System.out.println("Smallest quantity item: ");
        System.out.println("Lowest total dollar item: ");
        System.out.println("-----------------------------------------------------------------");
        inputFile.close();
    } catch (IOException e) {
        System.out.println("There was a problem reading from " + database);
    }
    in.close();
}
private static String getFile(Scanner inScanner) {
    System.out.print("Enter database filename: ");
    String fileName = inScanner.nextLine();
    return fileName;
}
private static void getTitle(ArrayList<String> Titles, String title) {
    Titles.add(title);
}
private static void getType(ArrayList<String> Types, String type) {
    Types.add(type);
}
private static void getPrice(ArrayList<Double> Prices, double price) {
    Prices.add(price);
}
private static void getQuantity(ArrayList<Integer> Quantities, int quantity) {
    Quantities.add(quantity);
}
private static void getLargestQuantityItem(ArrayList<Integer> Quantities){
    Integer largestQuantity = Collections.max(Quantities);
    }
}

这是输出和我收到的错误：

Enter database filename: 

Product Summary Report

------------------------------------------------------------
Title: The Shawshank Redemption
 Product Type: DVD
 Price: 19.95
 Quantity: 100

Title:  Dark Knight
 Product Type: DVD
 Price: 19.95
 Quantity: 50

Title: 
 Product Type: DVD
 Price: 9.95
 Quantity: 137

Title:  Girl With The Dragon Tattoo
 Product Type: Book
 Price: 14.95
 Quantity: 150

Title: 
 Product Type: DVD
 Price: 9.95
 Quantity: 55

Title:  Game of Thrones
 Product Type: Book
 Price: 8.95
 Quantity: 100

java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Scanner.java:838)
    at java.util.Scanner.next(Scanner.java:1347)
    at Project01.main(Project01.java:31)

Answer 1

参考 this post 和您的 txt 文件。

在您的 nextInt()、nextDouble() 方法之后添加 inputFile.nextLine()。

getQuantity(Quantities, inputFile.nextInt());
inputFile.nextLine();
getPrice(Prices, inputFile.nextDouble());
inputFile.nextLine();

更改以下代码

getType(Types, inputFile.nextLine());

并在 while 循环结束时删除 inputFile.next();。

第二种方法 将仅添加 if 块围绕您的 next(); 方法调用。

if (inputFile.hasNext()) {
    inputFile.next();
}

问题是 while 循环末尾的 next(); 正在读取下一个元素。但是在 Book 之后的文件末尾没有任何内容可读，因此它在该行抛出异常。

更新：

largestQuantity是局部变量，方法外不能访问。你应该 return 它来自 getLargestQuantityItem 方法。因此，更改方法的 return 类型，然后 return 最大值。

private static Integer getLargestQuantityItem(ArrayList<Integer> Quantities){
    return Collections.max(Quantities);
}

并且在 main 方法中

获得最大数量的项目：

System.out.println("Lowest total dollar item: ");
Integer largestQuantityMainVariable = getLargestQuantityItem(Quantities);
System.out.println("Largest quantity : " + largestQuantityMainVariable);

int index;
for (int i = 0; i < Quantities.size(); i++) {
    if (Quantities.get(i) != null && Quantities.get(i).equals(largestQuantityMainVariable)) {
        index = i;
        break;
    }
}

System.out.println("Largest quantity item : " + Titles.get(index));

更新 2：

对于评论中的问题The only thing I have left is to find the highest and lowest total dollar value. I need to somehow take the quantity times the price and then look for the max and min value out of those values

private static List<Double> generateTotalPriceList(List<Double> prices, List<Integer> quantities) {
    List<Double> totalPriceList = null;
    if (prices != null && prices.size() > 0
            && quantities != null && quantities.size() > 0) {
        if (prices.size() == quantities.size()) {
            totalPriceList = new ArrayList<Double>();
            double totalValue;
            for (int i = 0; i < prices.size(); i++) {
                totalValue = prices.get(i) * (double) quantities.get(i);
                totalPriceList.add(totalValue);
            }
        }
    }
    return totalPriceList;
}

在主要方法中

List<Double> totalPriceList = generateTotalPriceList(Prices, Quantities);

现在您可以按照我们为 Quantity 所做的步骤进行操作。

如何修复我的 NoSuchElementException？

How can I fix my NoSuchElementException?

java

exception-handling