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java - 在 Java 中找不到行

问题描述

我无法从文件中读取数据。我收到的错误是：

Exception in thread "main" java.util.NoSuchElementException: No line found
    at java.base/java.util.Scanner.nextLine(Scanner.java:1651)
    at Driver.readFile(Driver.java:20)
    at Driver.main(Driver.java:9)

我不明白为什么当明显更多时找不到该行。我的教授说通过在读取最后一行（ String temp）后创建一个临时变量来保存新行来清除缓冲区。我仍然得到同样的错误。清晰度将不胜感激。对不起，高级的长帖子。想展示所有工作以帮助大家理解我的问题。

这是我的驱动程序类：

import java.util.Scanner;

public class Driver {

public static void main(String[] args) {
    Pets [] pets = new Pets[25];
    
    int numPets = readFile(pets);
    System.out.println(numPets);
    
}
public static int readFile(Pets [] pets) {
    Scanner kb = new Scanner("pets.dat");
    
    int count = 0;
    while (kb.hasNext()) {
        
        String name = kb.nextLine();
        String owner = kb.nextLine();
        String species = kb.nextLine();
        String breed = kb.nextLine();
        double age = kb.nextDouble();
        double weight = kb.nextDouble();
        String temp = kb.nextLine();
        
        Pets pet = new Pets(name, owner, species, breed, age, weight);
        pets [count] = pet;
        count++;
    }
    return count;
}
}

如果需要，这是我的宠物课程：

public class Pets {

private String name;
private String owner;
private String species;
private String breed;
private double age;
private double weight;

Pets() {
    
}
Pets(String name, String owner, String species, String breed, double age, double weight) {
    this.name = name;
    this.owner = owner;
    this.species = species;
    this.breed = breed;
    this.age = age;
    this.weight = weight;
    
}
boolean isSpecies(String species) {
    if (this.species == species) {
        return true;
    }
    return false;
}
public String toString() {
    return "Name: " + name + "\n" + "Owner: " + owner + "\n" + "Species: " + species + "\n" + "Breed: " + breed + "\n" + "Age: " + age + "\n"  + "Weight: "+ weight;
}
}

这是数据文件：

Izzy
Liz Davidson
cat
domestic shorthair
2
10.5
Duncan
Sofia Berrios
dog
basset hound
9
56
Otis Redding
Scott Grasso
hamster
golden
0.5
0.1
Guinness
Kumar Chaudhuri
dog
mutt
6
32
Snape
Liping Xiang
snake
grass snake
3.5
0.5
Artemis
Ali Khan
cat
domestic shorthair
11
12
KD
Rachel Kauffman
dog
Akita
6
65
Morgan
Nick McEntire
cat
Russian blue
.8
8.4
Max
Kelly Luiselli
dog
mutt
15
38
Ingrid
Terry Dumas
snake
boa constrictor
3.5
4.6

标签： javafile

解决方案

您的代码中需要更改一些小东西。以下是您的代码以及我的更正。代码后的解释。

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Driver {

    public static void main(String[] args) {
        File source = new File("pets.dat");
        List<Pets> list = new ArrayList<Pets>();
        try (Scanner kb = new Scanner(source)) {
            while (kb.hasNextLine()) {
                String name = kb.nextLine();
                String owner = kb.nextLine();
                String species = kb.nextLine();
                String breed = kb.nextLine();
                String ageStr = kb.nextLine();
                double age = Double.parseDouble(ageStr);
                String weightStr = kb.nextLine();
                double weight = Double.parseDouble(weightStr);
                Pets pet = new Pets(name, owner, species, breed, age, weight);
                list.add(pet);
            }
        }
        catch (IOException xIo) {
            xIo.printStackTrace();
        }
        System.out.println("count = " + list.size());
    }
}

class Pets {
    private String name;
    private String owner;
    private String species;
    private String breed;
    private double age;
    private double weight;

    Pets() {
        
    }
    Pets(String name, String owner, String species, String breed, double age, double weight) {
        this.name = name;
        this.owner = owner;
        this.species = species;
        this.breed = breed;
        this.age = age;
        this.weight = weight;
        
    }
    boolean isSpecies(String species) {
        if (this.species == species) {
            return true;
        }
        return false;
    }
    public String toString() {
        return "Name: " + name + "\n" + "Owner: " + owner + "\n" + "Species: " + species + "\n" + "Breed: " + breed + "\n" + "Age: " + age + "\n"  + "Weight: "+ weight;
    }
}

由于您的问题是读取文件，因此我只是编写了一个main()方法来演示您应该如何读取文件。

请注意，while循环条件是kb.hasNextLine()而不是kb.hasNext()。您的数据文件每行包含一项数据。因此，您需要一次阅读一行。nextLine()这就是为什么我只在while循环内调用方法。您需要阅读一行并处理它。因此，我最初读取包含 adouble作为字符串的行，然后将该字符串转换为双精度。我从您的代码中删除了这一行：

String temp = kb.nextLine();

这不是必需的。我认为您的教授试图告诉您将年龄和体重读取为字符串，然后将每个字符串转换为双精度，就像我所做的那样。这就是为什么他建议使用临时变量。

此外，我将 a 存储Pets在 a而不是数组中，因为（理论上）a可以包含List多少个元素没有限制。List

阅读完所有内容后，关闭数据文件也很重要。这就是我使用try-with-resources的原因。

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