How to resolve the error in java : Exception in thread "main" java.lang.NullPointerException in an online compiler

Asked Sep 28 '20 at 11:09

Active Sep 28 '20 at 11:24

Viewed 38 times

I have written a simple code to read a 2d integer array of size n1 and n2 and print the middle element in java.

import java.io.*;
import java.lang.*;
import java.util.*;
public class Main {
    public static void main(String args[])throws IOException {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        int n1=Integer.parseInt(br.readLine());
        int n2=Integer.parseInt(br.readLine());
        int[][] arr=new int[n1][n2];
        System.out.println("n1"+n1+"n2="+n2);
        String[] sarr=new String[n2];
        for(int i=0;i<n1;i++) {
            sarr = br.readLine().split(" ");//line 13
            for (int j = 0; j < n2; j++)
                arr[i][j] = Integer.parseInt(sarr[j]);
        }
        System.out.println(arr[n1/2][n2/2]);
    }
}

I was getting the below error in an online compiler but when executed in intellijIDEA there was no error.

Exception in thread "main" java.lang.NullPointerException
    at Main.main(Main.java:13)

edited Sep 28 '20 at 11:24

asked Sep 28 '20 at 11:09

Sasirekha MSVL

2

If you are getting this error in an online compiler, it probably means that it has some limitations. You are reading something from System.in, which is probably not supported properly there. – rapasoft Sep 28 '20 at 11:13
5

A `readLine()` call will return `null` when you get to the end of the file. – Stephen C Sep 28 '20 at 11:13
1

@rapasoft To be able to get to line 13 means it does support some input, else `int n1=Integer.parseInt(br.readLine())` would throw. Looks like OP did not define enough input data – Michael Sep 28 '20 at 11:14
2

@Michael true, but if he used the same input in Intellij IDEA where it works for him (which I suppose he did), it might be the problem with that environment. Anyhow, without additional inputs it's hard to tell. – rapasoft Sep 28 '20 at 11:16
1

I think you got NumberFormatException in line 13. – Sadman Sobhan Sep 28 '20 at 11:16
1

@SadmanSobhan no, just no. What gives you that impression? – luk2302 Sep 28 '20 at 11:17
This code won't work in IntelliJ either because at `arr[i][j] = ...` you will certainly run into problems because you never initialized `arr[i]`. – luk2302 Sep 28 '20 at 11:18
@luk2302 it worked perfectly in intellijIDEA – Sasirekha MSVL Sep 28 '20 at 11:22
You have hadcoded the size String[] sarr=new String[3]; this should be equal to the number of rows – Umesh Sanwal Sep 28 '20 at 11:22
@UmeshSanwal I just checked by placing it manually even though i gave n2=3 as input – Sasirekha MSVL Sep 28 '20 at 11:25
@SadmanSobhan No I got the above error. – Sasirekha MSVL Sep 28 '20 at 11:28
@StephenC I did not understand correctly what you said – Sasirekha MSVL Sep 28 '20 at 11:29
1

Works perfectly fine for me. Can you paste your input – Umesh Sanwal Sep 28 '20 at 11:33
Thanks everyone for your valuable time. I have found out that there was an error in the online compiler while taking the input . in sample test cases they mentioned the sample test cases are in format – Sasirekha MSVL Sep 28 '20 at 11:46
5 5\n 1 2 3 4 5\n 6 7 8 9 10\n 1 2 3 4 5\n 6 7 8 9 10\n 1 1 1 1 1\n – Sasirekha MSVL Sep 28 '20 at 11:46
but in hidden test cases they took in another format – Sasirekha MSVL Sep 28 '20 at 11:47
3\n 3\n 6 7 9 -7 -4 -3 -4 -3 -2\n – Sasirekha MSVL Sep 28 '20 at 11:47
Thanks @UmeshSanwal i understood. – Sasirekha MSVL Sep 28 '20 at 11:48
1

What I said means this: "If readLine() returns null *then* you are at the end of file". >>Your<< task would be to figure out why you are at the end of file when your code doesn't expect that. – Stephen C Sep 28 '20 at 23:12

How to resolve the error in java : Exception in thread "main" java.lang.NullPointerException in an online compiler

0 Answers0