NullPointerException with jagged array

Asked Mar 08 '18 at 04:39

Active Mar 08 '18 at 04:53

Viewed 22 times

I am having trouble seeing what is causing my error. Code is below and below that is the error message I am receiving. Thank you.

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

public class IO {

public static void main(String[] args) throws Exception {
    File inFile = new File("src/passign6/grades.txt");
    File outFile = new File("src/passign6/finalgrades.txt");

    try (
            Scanner input = new Scanner(inFile);
            PrintWriter output = new PrintWriter(outFile);) {

        int[][] grades = new int[42][];
        for (int i = 0; input.hasNextLine() && i < grades.length; i++) {
            String line = input.nextLine();
            Scanner input2 = new Scanner(line);
            for (int j = 0; input2.hasNextInt() && j < grades[i].length; j++) {
                grades[i][j] = input.nextInt();
            }

            input.close();
            output.close();
        }

    }

}
}

Exception in thread "main" java.lang.NullPointerException
at io.IO.main(IO.java:20)

edited Mar 08 '18 at 04:53

Sotirios Delimanolis

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asked Mar 08 '18 at 04:39

Mike Brown

2

What do you think `new int[42][];` does? – Sotirios Delimanolis Mar 08 '18 at 04:41
Created ragged array based off of input file – Mike Brown Mar 08 '18 at 04:42
No input file is involved in that expression. It initialized the "first dimension". The second dimension is just a bunch of `null`s. – Sotirios Delimanolis Mar 08 '18 at 04:44
Are you able to explain what I can change to fix that? Do I need to move my array? – Mike Brown Mar 08 '18 at 04:47
You need to initialize each element of that first dimension. `grades[i] = new int[someSize];` – Sotirios Delimanolis Mar 08 '18 at 04:48
Ok thank you for the help. I will work on that. – Mike Brown Mar 08 '18 at 04:52

NullPointerException with jagged array

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