从. txt文件扫描时出现Java . util . inputmismatchexception错误

Question

我正在创建一个使用2个类的程序。在一个类中，我创建方法，然后由第二个类调用。所有方法都包含在第一个类中，第二个类只是调用它们并执行代码。

第 1 类

 import java.io.File;
 import java.io.FileNotFoundException;
 import java.util.Scanner;


 public class Student {


    private Scanner scanner;
    private String firstName;
    private String lastName;
    private int homeworkScore;
    private int testScore;
    private String letterGrade;
    private int numberOfStudents;

    public Student () {

        String firstName = null;
        String lastName = null;
        int homeworkScore = 0;
        int testScore = 0;
        String letterGrade = null;
        int numberOfStudents = 0;
    }


    public void openFile(){
        try { 
            scanner = new Scanner(new File("grades.txt"));
        } catch (FileNotFoundException e) { 
            System.out.println("Error opening file. Please make sure that you have a grades.txt file in the same folder as GradeCalculator.class");
            System.exit(0); 
        }
    }


    public void setNumberOfStudents() {
        System.out.println("It kinda works");
        numberOfStudents = scanner.nextInt();
    }

 public void setFastName() {
        fastName = scanner.next();
    }

 public void setLastName() {
        lastName = scanner.next();
    }

public void setHomeworkScore() {

        int subAssignment = 0;
        int assignment = 0;

        for(int i = 1; i <= 21; i++) { 
            subAssignment = scanner.nextInt();
            assignment += subAssignment;
        }

        homeworkScore = assignment;
    }

第二类

  import java.io.File;
  import java.io.FileNotFoundException;
  import java.util.Scanner;


 public class CourseGrade {

public static void main(String[] args) {

    Student myStudent = new Student();

    myStudent.openFile();

    myStudent.setNumberOfStudents();

    myStudent.setFirstName();

    myStudent.setLastName();

    myStudent.setHomeworkScore();


}

 }

这是我得到的错误:

 It kinda works
 Exception in thread "main" java.util.InputMismatchException
 at java.util.Scanner.throwFor(Unknown Source)
 at java.util.Scanner.next(Unknown Source)
 at java.util.Scanner.nextInt(Unknown Source)
 at java.util.Scanner.nextInt(Unknown Source)
 at Student.setHomeworkScore(Student.java:54)
 at CourseGrade.main(CourseGrade.java:20)

...“它有点工作”语句只是为了看看它是否正确调用了该方法，看起来确实如此。

根据我的理解，这个错误告诉我它从。txt文件，但idk为什么会这样。它能正确读取文件吗？任何类型的帮助都很好，因为我已经盯着这段代码看了几个小时了！

Answer 1

根据oracle java留档，当令牌不符合请求的模式（int）或超出范围时，会引发该异常。

如果文件中不再有int，就会抛出异常。< br >您可以通过检查是否有另一个int值要用Scanners方法hasNextInt读取来避免该异常。

例如：

for(int i = 1; i <= 21 && scanner.hasNextInt(); i++) { 
            subAssignment = scanner.nextInt();
            assignment += subAssignment;
}

(如果这不能解决您的问题，您还应该包括您的输入文件)

Answer 2

根据错误消息以及错误发生的位置，很可能您正在尝试读取一个整数，但您正在读取的实际数据不是数字。

您可以通过将您的< code>scanner.nextInt()更改为< code>scanner.next()并打印出您实际获得的值来验证这一点。或者，您可以添加以下形式的“错误处理”:

    for(int i = 1; i <= 21; i++) { 
        if (scanner.hasNextInt()
          subAssignment = scanner.nextInt();
        else
          throw new RuntimeException("Unexpected token, wanted a number, but got: " + scanner.next());
        assignment += subAssignment;
    }