How do you parse input from a text file in JAVA?

Question

I tried to parse the String from my input.txt file, but I get the NumberFormatException thrown every time. I've added all the code that I have so far. I have tried .trim as well. I am very new to text files in Java; therefore, I have no idea what is wrong here. However, any bit of help would be appreciated.

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class Lab5_Exceptions_Redo extends Exception {

    public static void main(String[] args) throws FileNotFoundException {

        String file = "inputt.txt";
        String file1 = "outputt.txt";
        String file2 = "errorr.txt";

        PrintWriter errorr = new PrintWriter(file2);

        PrintWriter inputt = new PrintWriter(file);
        inputt.println(15951);
        // int whatever = Integer.parseInt(file);
        // System.out.print(whatever);
        inputt.close();
        Scanner scan = new Scanner(file);
        String number = scan.nextLine();
        int num = Integer.parseInt(number.trim());
        System.out.printf("%d", num);

        PrintWriter outputt = new PrintWriter(file1);
        outputt.println(num);
        outputt.close();
        // inputt.close();

        scan.close();
        // System.out.printf("%d", num);

        try {

        } catch (InputMismatchException e) {
            errorr.println("There was an input mismatch error.");
        } catch (NoSuchElementException e) {
            errorr.println("There is no such element.");
        } catch (UnsupportedOperationException e) {
            errorr.println("An unsupported operation occured.");
        } catch (NumberFormatException e) {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
        errorr.close();

    }
}

Did you try debugging the issue?. What do you see when you try to print num? — TheLostMind
– TheLostMind, Commented Mar 28, 2016 at 7:03

Rahman · Accepted Answer · 2016-03-28 07:13:12Z

4

You are doing a mistake. In Scanner constructor you should pass File object not String object. Since you are passing string "inputt.txt" its trying to parse this string and as a result you are getting NFE. Try this

Scanner scan = new Scanner(new File(file));

answered Mar 28, 2016 at 7:13

Rahman

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Comments

ninja.coder · Accepted Answer · 2016-03-28 07:05:27Z

0

You must be getting the whitespaces along with the input while doing nextLine(). Use trim() function to get rid of any whitespaces.

int num = Integer.parseInt(number.trim());

Alternatively, you can try using nextInt() instead of nextLine().

Here is the JAVA Doc of parseInt():

Parses the string argument as a signed decimal integer. The characters in the string must all be decimal digits, except that the first character may be an ASCII minus sign '-' ('\u002D') to indicate a negative value or an ASCII plus sign '+' ('\u002B') to indicate a positive value. The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to the parseInt(java.lang.String, int) method.

edited Mar 28, 2016 at 7:05

answered Mar 28, 2016 at 7:01

ninja.coder

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2 Comments

SlackStack Over a year ago

I tried the .trim, and unfortunately it does not work \: . I am very new to creating text files in Java, and that is why I am so confused as to why it will not parse the integer from the input text file.

Rahman Over a year ago

This is not the actual root cause

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