Trouble reading integer from text file

Question

I have a text file (data.txt) with the following lines:

1   3   t1  a   b   c   d   1
2   1   t2  a   b   c   d   3

The values are separated by tabs and each line represents a new object. I'm reading data from the file and using it to create an object. I've been able to read the first 7 values, but when I reach the integer at the end, the scanner is unable to read it and I get an InputMisMatchException.

This is what I'm getting right now:

ID: 1
Category: 3
Title: t1
Option 1: a
Option 2: b
Option 3: c
Option 4: d
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.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at TestApp.readFile(TestApp.java:35)
    at TestApp.main(TestApp.java:9)

But I'm expecting something like this:

ID: 1
Category: 3
Title: t1
Option 1: a
Option 2: b
Option 3: c
Option 4: d
Result: 1
ID: 2
Category: 1
Title: t2
Option 1: a
Option 2: b
Option 3: c
Option 4: d
Result: 3

I have a Test class and a TestApp class to run the code

Test class:

import java.util.ArrayList;

public class Test {
    private int ID;
    private int category;
    private String title;
    private ArrayList<String> options;
    private int results;

    public Test(int ID, int category, String title, ArrayList<String> options, int result) {
        this.ID = ID;
        this.category = category;
        this.title = title;
        this.options = options;
        this.results = result;
    }
}

TestApp:

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

public class TestApp {
    public static void main(String[] args) {
        ArrayList<Test> tests = new ArrayList<>();
        readFile(tests, "data.txt");
    }

    public static void readFile(ArrayList<Test> tests, String inputFile) {
        File testFile = new File(inputFile);
        ArrayList<String> optionsList = new ArrayList<>();
        try {
            Scanner input = new Scanner(testFile);
            input.useDelimiter("[\t\n]");

            // Read data
            while(input.hasNext()) {
                int ID = input.nextInt();
                System.out.println("ID: " + ID);
                int category = input.nextInt();
                System.out.println("Category: " + category);
                String title = input.next();
                System.out.println("Title: " + title);
                String option1 = input.next();
                System.out.println("Option 1: " + option1);
                String option2 = input.next();
                System.out.println("Option 2: " + option2);
                String option3 = input.next();
                System.out.println("Option 3: " + option3);
                String option4 = input.next();
                System.out.println("Option 4: " + option4);
                int result = input.nextInt();
                System.out.println("Result: " + result);

                // Add to ArrayList
                optionsList.add(option1);
                optionsList.add(option2);
                optionsList.add(option3);
                optionsList.add(option4);

                // Create object
                Test newTest = new Test(ID, category, title, optionsList, result);
                // Add to test bank
                tests.add(newTest);
                // Clear ArrayList
                optionsList.clear();
            }
        } catch (FileNotFoundException error) {
            System.out.println("File not found");
        }
    }
}

I don't understand why the code fails at int result = input.nextInt(); when it was able to read the prior values. How can I fix this?

I bet you're on Windows, and that the text file uses \r\n as line terminators, and since you replaced the default delimiter of "\\p{javaWhitespace}+" with a simplified "[\t\n]" that doesn't handle \r\n pairs, or \r at all, the token seen is "1\r", which is not a valid integer value. Try useDelimiter("[\t\n]|\r\n") — Andreas
– Andreas, Commented Apr 15, 2021 at 21:53
Use try-with-resource for your Scanner, like this : try (Scanner input = new Scanner(testFile)) { to avoid memory leak. But in real world, use files JSON or XML with jackson, jaxb or Java built-in DOM parser. — Stéphane Millien
– Stéphane Millien, Commented Apr 15, 2021 at 22:21

Manuel González Costa · Accepted Answer · 2021-04-15 22:00:40Z

1

What's giving you trouble is the useDelimiter() function.

I have tested the code and if you comment the line input.useDelimiter("[\t\n]"); it works fine and returns the correct output.

answered Apr 15, 2021 at 22:00

Manuel González Costa

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1 Comment

Andreas Over a year ago

Simply removing the useDelimiter() call is very likely not the right solution. OP likely added it for a reason, e.g. so input 1\t3\tt1\ta\t\t\td\t1 would correct be read as meaning that options 2 and 3 are empty strings, i.e. consecutive tab characters are treated as multiple delimiters.

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