Java程序中的空指针异常

Question

Question: you have to check for n test cases that multiplication of a and b is equal to 3rd input value or not.If equal then print YES otherwise NO. Input: 2 5 6 30 4 3 20

Output: YES NO

Explanation: 2 is number of test cases. 5 is a & 6 is b ,multiplication is 30 so YES

Constraints :

0 < test cases <= 1000000000 0 < a < b <= 10000000

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.Scanner;


class ques1 
{
    public static void main(String[] args) throws Exception
    {

        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        Scanner sc=new Scanner(System.in);
        BigInteger test=new BigInteger(sc.next());

        while(!test.equals(BigInteger.ZERO))
        {
            Scanner s=new Scanner(br.readLine());
            s.useDelimiter(" ");
            BigInteger p=new BigInteger(s.next());
            BigInteger q=new BigInteger(s.next());
            BigInteger r=new BigInteger(s.next());
            if(p.multiply(q).equals(r))
            {
                System.out.println("YES");
            }
            else
            {
                System.out.println("NO");
            }
            test=test.subtract(BigInteger.ONE);
        }
    }
}

This program is working fine in eclipse.But while running on online compilers like ideone.com,etc it is giving error message as following:

Exception in thread "main" java.lang.NullPointerException
    at java.io.StringReader.<init>(StringReader.java:50)
    at java.util.Scanner.<init>(Scanner.java:702)
    at ques1.main(Main.java:18)

Constraints are so big so i am using biginteger.I had also used stringtokenizer instead of scanner of input separation,but it is also giving same error. i have to take input in a spacing format so i am using stringtokenizer or scanner. Is there is any other way to separate them.

Answer 1

br.readLine() will return null when reaching the end of the file. And new Scanner(String) won't accept null as parameter. Apart from that you should always check for valid input / if you can read data from a resource.