Why am I getting NumberFormatException?

Question

I did a question in CodeChef platform and the code is getting executed well in my IDE and not in CodeChef Platform.

The same is the case when I use Scanner in place of Buffered Reader, I get NoSuchElementException.

Exception in thread "main" java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:542)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Codechef.main(Main.java:13)

Here is the link to the question : https://www.codechef.com/problems/LAYERS

/* package codechef; // don't place package name! */

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

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
{
    public static void main (String[] args) throws java.lang.Exception
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine());
        while (T>0)
        {
            StringTokenizer st = new StringTokenizer(br.readLine());
            int N = Integer.parseInt(st.nextToken());
            int C = Integer.parseInt(st.nextToken());
            int L[] = new int [N];
            int B[] = new int [N];
            int c[] = new int [N];
            int maxL =0, maxB=0;
            for(int i = 0;i<N;i++)
            {
                st = new StringTokenizer(br.readLine());
                L[i] = Integer.parseInt(st.nextToken());
                B[i] = Integer.parseInt(st.nextToken());
                c[i] = Integer.parseInt(st.nextToken());
                if(maxL<L[i])
                    maxL = L[i];
                if(maxB<B[i])
                    maxB = B[i];
            }
            int Graph[][] = new int[maxL/2][maxB/2];
            for(int i=0;i<N;i++)
            {
                for(int j=0;j<L[i]/2;j++)
                {
                    for(int k=0;k<B[i]/2;k++)
                    {
                      Graph[j][k]= c[i];
                    }
                }
            }
            int result[] =new int [C];
            for(int i=0;i<maxL/2;i++)
            {
                for(int j=0;j<maxB/2;j++)
                {
                    if(Graph[i][j]>0)
                    {
                        result[Graph[i][j]-1]++;
                    }
                }
            }
            for(int i=0; i<C;i++)
            {
                System.out.print(result[i]*4+" ");
            }
            T--;
        }
    }
}

Help me why I am getting the Error.

Answer 1

If I can count to line 13 (which is always shaky in code posted here), your exception is coming from this line:

int T = Integer.parseInt(br.readLine());

br.readLine() returns null when there is no more input. Since this is your first call to readLine(), it means that your input is empty. The null in your exception message means that a null was passed to parseInt (or the string "null", but that’s unlikely).

This explanation for your error also agrees with your reported NoSuchElementException from Scanner.

Tip: I know that your variables come from a problem statement that used T, N, C, L and B in uppercase. Still in Java, let the Java naming conventions win: use lowercase for variables. So t or capitalT. The variable name T is particularly confusing since T is very often used as a type parameter in generics.