收到 InputMismatch 错误，我不知道为什么

Question

当我尝试运行该程序时，我目前收到此错误。 代码编译得很好，但是当我尝试运行程序时，它给了我这个异常

Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Scanner.java:939)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextDouble(Scanner.java:2564)
    at Runner.main(Runner.java:23)

我尝试注释掉分隔符，但它给了我这个错误

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Box.getSurfaceArea()" because "<parameter1>[<local5>]" is null
    at Runner.averageSurfaceArea(Runner.java:33)
    at Runner.main(Runner.java:25)

老实说，我不明白为什么会出现这些错误，也不知道该怎么做。 这是跑步者 class 和 object 类/

//runner 
import java.util.Scanner;
import java.io.File;
import java.io.IOException;

class Runner{
    public static void main(String [] args) throws IOException{
        File f = new File ("input.txt");
        Scanner scan =  new Scanner(f);
        int i = 0;
        int count = 0;
        int index = 0; 
        while(scan.hasNextLine()){//getting the array size
            scan.nextLine();
            count++;
        }
        Scanner scan2 = new Scanner(f);
        scan2.useDelimiter(" ");
        Box [] boxarr = new Box [count]; // Box array 
        while(scan2.hasNextDouble()){
            boxarr[i] = new Box();
            boxarr[i].setLength(scan2.nextDouble());//setting atrubutes
            boxarr[i].setHeight(scan2.nextDouble());
            boxarr[i].setWidth(scan2.nextDouble());
        }
        averageSurfaceArea(boxarr);//uses this method to get average surface area
        index = getBigBox(boxarr); // gets the largest box
    }

    public static double averageSurfaceArea(Box [] arr){ 
        double average = 0; 
        double surfaceAreaTotal = 0;
        for(int i = 0; i<arr.length;i++){
            surfaceAreaTotal = surfaceAreaTotal + arr[i].getSurfaceArea(); 
        }
        average = surfaceAreaTotal / arr.length;
        return average; 
    }

    public static int getBigBox(Box [] arr){
        int index = 0;
        for(int i = 0 ; i<arr.length-1; i++){
            if(arr[i].compareTo(arr[i+1])){
                index = i;
            }else{
                index = i+1;
            }
        }
        return index;
    }

}

//object class
public class Box{
    private double length;
    private double height;
    private double width;

    Box(){}
    //constructures
    Box(double length, double height, double width){
        this.length = length;
        this.height = height;
        this.width = width;
    }
    //setters
    public void setLength(Double length){
        this.length = length;
    }

    public void setHeight(Double height){
        this.height = height;
    }
    public void setWidth(Double width){
        this.width = width;
    }
    //getters
    public double getLength(){
        return this.length;
    }
    public double getHeight(){
        return this.height;
    }
    public double getWidth(){
        return this.width;
    }
    //Gets the surface area 
    public double getSurfaceArea(){
        return 2*(this.length*this.width + this.length*this.height + this.width*this.height); 
    }
    //compares the box objects
    public boolean compareTo(Box box){
        return 2*(this.length*this.width + this.length*this.height + this.width*this.height) >= box.getSurfaceArea();
    }


}

这是输入文件。 它被命名为 input.txt

8.2 17.1 2.9
3.4 4.6 3.1 
1.4 19.9 1.6 
4.9 6.7 5.3 
18.5 2 16.3
4.0 7.2 10.8

任何帮助表示赞赏！

Answer 1

double 中的分隔符在您的系统上可能不同，eq "," 您可以通过更改 "." 来检查它是否有效。 到 "," 或者只是在扫描仪上设置区域设置：

Scanner scanner = new Scanner(System.in).useLocale(Locale.US);

Answer 2

在您的跑步者 class 中，删除您的第 20 行，即 scan2.useDelimiter(" "); 并且您的代码应该可以正常运行。在 java 中，delimiter 方法默认在扫描仪中搜索空格，因此您不需要使用 delimiter 方法。
除此之外，您不会增加变量“i”。在您的 while 循环中，在第 26 行之后包含 i++。 此外，在您的第 10 行 File f = new File ("input.txt"); 写入输入文件的完整路径，而不是写入文件名。 修复这三件事，您的代码将为您提供所需的 output。