Why does it throw an exception when reading int array from file in java

Question

I am trying to read an integer array from a file. the file format is as follows:

893

410

243

264

357

33

793

...

...

I will later split that array into 4 and calculate it's sum using MPI, but i can't seem to be able to read the file. I get this exception:

java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at runtime.starter.MulticoreStarter$1.run(MulticoreStarter.java:281)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NumberFormatException: For input string: "893"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at lab3.main(lab3.java:28)
... 6 more

Process finished with exit code 0

So from what i understand, the format of the read string is not correct to be cast as an integer, here is the Code:

        //create an array of length 400
        int[] array = new int[400];

        //read the array from the file using the scanner class
        try {
            Scanner scanner = new Scanner(new File("random1000.txt"));
            for (int i = 0; i < array.length; i++) {
                array[i] = Integer.parseInt(scanner.nextLine());

            }
        }
        catch (FileNotFoundException e) {
            System.out.println("File not found");
        }

I also tried scanner.nextInt() and Integer.valueof() instead of parseInt, here is the error i got for scanner.nextInt()

java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at runtime.starter.MulticoreStarter$1.run(MulticoreStarter.java:281)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:864)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextInt(Scanner.java:2117)
at java.util.Scanner.nextInt(Scanner.java:2076)
at lab3.main(lab3.java:30)
... 6 more

It is my first time using the Scanner class and i am fairly new to java, what am i doing wrong and how do i fix this?

Here is the FULL code, i haven't tested any of the mpi stuff out yet, but i tried reading the file without the mpi code and i had the same problem.

import mpi.*;

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

public class lab3 {


//Build a program that sums a big array (for example 1000 elements) over four processes
public static void main(String[] args) {

    //initialize MPI
    MPI.Init(args);

    //get the rank of the process
    int rank = MPI.COMM_WORLD.Rank();

    //if the rank is 0
    if (rank == 0) {
        // read the array from the file
        int[] array = new int[400];

        //read the array from the file using file reader
        try {
            Scanner scanner = new Scanner(new File("random1000.txt"));
            for (int i = 0; i < array.length; i++) {
                array[i] = scanner.nextInt();

            }
        }
        catch (FileNotFoundException e) {
            System.out.println("File not found");
        }


        //divide the array into 4 parts and send it to the other processes
        int[] array1 = new int[array.length / 4];
        int[] array2 = new int[array.length / 4];
        int[] array3 = new int[array.length / 4];
        int[] array4 = new int[array.length / 4];
        for (int i = 0; i < array.length / 4; i++) {
            array1[i] = array[i];
            array2[i] = array[i + array.length / 4];
            array3[i] = array[i + array.length / 2];
            array4[i] = array[i + array.length / 4 + array.length / 2];
        }
        //send each part to the other processes
        MPI.COMM_WORLD.Send(array2, 0, array2.length, MPI.INT, 1, 0);
        MPI.COMM_WORLD.Send(array3, 0, array3.length, MPI.INT, 2, 0);
        MPI.COMM_WORLD.Send(array4, 0, array4.length, MPI.INT, 3, 0);

        //calculate the sum of the array 1
        int sum1 = 0;
        for (int i = 0; i < array1.length; i++) {
            sum1 += array1[i];
        }

        //receive the summation from the other processes
        int sum2 = 0;
        MPI.COMM_WORLD.Recv(sum2 ,0, 0, MPI.INT, 1, 0);
        int sum3 = 0;
        MPI.COMM_WORLD.Recv(sum3 ,0, 0, MPI.INT, 2, 0);
        int sum4 = 0;
        MPI.COMM_WORLD.Recv(sum4 ,0, 0, MPI.INT, 3, 0);

        //calculate the final sum
        int sum = sum1 + sum2 + sum3 + sum4;

        //print the final sum
        System.out.println("The Final sum is: " + sum);

        //finalize MPI
        MPI.Finalize();
    }
    else {
        //receive the array from the process 0
        int[] array = new int[1000 / 4];
        MPI.COMM_WORLD.Recv(array, 0, array.length, MPI.INT, 0, 0);

        //calculate the sum of the array
        int sum = 0;
        for (int i = 0; i < array.length; i++) {
            sum += array[i];
        }

        //send the sum to the process 0
        MPI.COMM_WORLD.Send(sum, 0, 0, MPI.INT, 0, 0);
        //print local sum and rank
        System.out.println("The sum of the array is: " + sum + " and the rank is: " + rank);
    }
}


}

IntelliJ Idea , Windows 11.

EDIT:

i tried doing it this way:

List<Integer> ints = Files.lines(Paths.get("random1000.txt"))
                    .map(Integer::parseInt)
                    .collect(Collectors.toList());
array = ints.stream().mapToInt(i -> i).toArray();

throws java.lang.NumberFormatException: For input string: "893"

Answer 1

I created a new file and added some random numbers manually and it worked, to my understanding, the random number generator I used to create the text file might have added some extra bytes at the beginning which might be the cause of the problem.