NullPointerException - reading not empty file returns Null

Question

I'm fairly new to programming and I wanted to learn how to read data from a file. I watched this video and tried to copy the idea for my own purpose. https://www.youtube.com/watch?v=3RNYUKxAgmw

Whenever I try to run my main it says Error Line 22 - NullPointerException. I have a text file with numbers and I have checked if the names match. I simply do not understand why it says my file is empty.

package uge4;
import java.util.*;
import java.io.*;

public class ReadFile {

    private Scanner x;
    public void openFile () {
        try {
            x = new Scanner (new File("gradeconverter.txt"));
        } catch(FileNotFoundException e){
            System.out.println("File not found.");
        }
    }

    public void readFile() {
        Scanner input = new Scanner(System.in);
        System.out.print("Insert old grade ");
        int grade = input.nextInt();
        input.close();

    // line 22 
    while(x.hasNextInt()) {
        int a = x.nextInt();
        int b = x.nextInt();
        if ( a == grade) {
            System.out.println("Your new grade is: "+b);
        }
    }
}

public void closeFile() {
    x.close();
}
}

This is my .txt file 13 12 11 12 10 10 9 7 8 7 7 4 6 2 5 0 3 0 0 -3 — Tacolips
– Tacolips, Commented Oct 20, 2015 at 9:45
I suspect what's actually happened is that your x variable is null. Was there a "File not found." prompt in the console when you ran it? Had you actually called openFile() before you called readFile()? — JonK
– JonK, Commented Oct 20, 2015 at 9:47
Usually "NullPointerExeption" means that something is not initialized, try to debug it — Shell Scott
– Shell Scott, Commented Oct 20, 2015 at 9:52
This is the order of my main. ReadFile r = new ReadFile(); r.openFile(); r.readFile(); r.closeFile(); — Tacolips
– Tacolips, Commented Oct 20, 2015 at 9:52

TheNorthon · Accepted Answer · 2015-10-20 09:57:49Z

2

After first int a = x.nextInt() calls another int b = x.nextInt();, it may happend that x Scanner has no more data to return. You need to check x.hasNextInt() before each call of x.nextInt() method.

answered Oct 20, 2015 at 9:57

TheNorthon

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Parth Anjaria · Accepted Answer · 2015-10-20 09:57:33Z

0

i guess it is because you havnt specified the path of your file

if you are uding a file from your pc/latop's harddisk please give the complete path

x = new Scanner (new File("C://newfolder//gradeconverter.txt"));// just an example, add the actual path of you files location

answered Oct 20, 2015 at 9:57

Parth Anjaria

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2 Comments

Tacolips Over a year ago

It worked! thanks a lot for all the help every1 :) now.. is there a way to set default pathing? So if i save the file under my workspace i would not have to add the path each time

Parth Anjaria Over a year ago

@Tacolips you can take an global variable where you add the path of your external directory(or workspace) and the n give that variable each and every place

Manu Zi · Accepted Answer · 2015-10-20 09:59:47Z

0

Can u simply use the java 8 "way"

Files.lines(Paths.get(FILE_PATH)).forEach(System.out::print);

PS: You have forget to open the Scanner -> x

answered Oct 20, 2015 at 9:59

Manu Zi

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