Getting a InputMismatch error and I don't know why

Question

I am currently getting this error when I try to run the program. The code compiles fine but when I try to run the program, it gives me this exeception

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)

I tried commenting out the delimiter but it gives me this error

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)

Honestly I do not understand why I am getting these errors and I do not know what to do. Here is the runner class and object class/

//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();
    }


}

This is the input file. It is named 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

Any help is appreciated!

Answer 1

Delimiter in double can be different on your system, eq "," You can check if it works by changing "." to "," or just set locale on Scanner:

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

Answer 2

In your runner class, delete your 20th line which is scan2.useDelimiter(" "); and your code should run just fine.In java, delimiter method by default searches for whitespace in scanner so you don't need to use the delimiter method.
Along with this, You are not incrementing your variable "i".In your while loop, include i++ after your 26th line. Also, In your 10th line File f = new File ("input.txt"); Write the complete path of your input file rather than writing the name of the file. Fix these 3 things and your code will give you the desired output.