How do I fix a NoSuchElementException from a input file?

Question

I was wondering if anyone could help solve this NoSuchElements exception in my program which scans a text very large text and then is added to the ArrayList.

I have tried re-arranging the order of the code to see if that would fix it but now I don't know how to fix it.

Exception itself:

Exception in thread "main" java.util.NoSuchElementException
    at java.base/java.util.Scanner.throwFor(Scanner.java:937)
    at java.base/java.util.Scanner.next(Scanner.java:1478)
    at mainTest.main(mainTest.java:11)

mainTest class:

import java.io.*;
import java.util.*;

public class mainTest {
    public static void main(String args[]) throws FileNotFoundException {
        ArrayList<String> bigBoi = new ArrayList<>(500000);

        Scanner scan1 = new Scanner(new File("LargeDataSet.txt"));

        while (scan1.hasNextLine()) {
            scan1.next();
            String data = scan1.next() + " " + scan1.next();
            bigBoi.add(data);
        }

        ArrayList<String> successful = new ArrayList<>(500000);
       }
    }

The unit of a .txt file : https://drive.google.com/file/d/1MWfMKMhSvuopOt9WwquABgYBTt0M4eLA/view?usp=sharing

(sorry for needing you to download it from a google drive, the file is so long I probably would've been reported or something if I had pasted 500,000 lines)

It would have been more helpful if you shared the exception logs as well. — Shubham Marathia, Jan 03 '20 at 03:43
Yes it has three strings in each line. First one is an int and the other two are one first name string and one last name. — Walter Medly, Jan 03 '20 at 03:49
https://stackoverflow.com/a/50750997/9020698 I believe LargeDataSet.txt is not there in your classpath. You can try by providing a full path. — Mayank Pande, Jan 03 '20 at 03:56

score 1 · Accepted Answer · answered Jan 03 '20 at 03:56

1

Please check with scan1.hasNext() instead of scan1.hasNextLine():

while (scan1.hasNext()) {
        scan1.next();
        String data = scan1.next() + " " + scan1.next();
        bigBoi.add(data);
}

answered Jan 03 '20 at 03:56

Anuradha

570
6
20

score 0 · Answer 2 · answered Jan 03 '20 at 04:43

There is an empty line at the end of LargeDataSet.txt which is valid for scan1.hasNextLine() check, but the scan1.next() throws NoSuchElementException as there's nothing to read.

Changing validation to scan1.hasNext() as suggested in the accepted answer, solves that problem, but the program could still crash if there are less than 3 entries on any line and accepts lines with more than 3 entries.

A better practice is to validate all externally supplied data:

while (scan1.hasNextLine()) {
    String line = scan1.nextLine();
    String[] tokens = line.split("\\s+"); //split by space(s)
    if(tokens.length != 3) { //expect exactly 3 elements on each line
        throw new IllegalArgumentException("Invalid line: " + line);
    }
    bigBoi.add(tokens[1] + " " + tokens[2]);
}

How do I fix a NoSuchElementException from a input file?

2 Answers2