Question

This is my solution for sphere’s online judge palin problem. It runs fine on Netbeans, but the judge is rejecting my answer saying it gives a RuntimeError. I tried it on JCreator and it says:

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
    at java.lang.Integer.parseInt(Integer.java:468)
    at java.lang.Integer.parseInt(Integer.java:497)
    at Main.main(Main.java:73)

I’m not passing an empty string for it to parse, why is this?

The code:

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



class Main {

    public static int firstPalinLargerThanNum(int num){

        int foundPalin =0;

        int evalThisNum = ++num;

        while (true){


        if (isPalin(evalThisNum))


            break;

        evalThisNum++;
        }

        foundPalin = evalThisNum;
        return foundPalin;

    }

    public static boolean isPalin(int evalThisNum){

           boolean isItPalin = false;

           int dig=0;
           int rev=0;


          int  n = evalThisNum;

          while (evalThisNum > 0)
          {

           dig = evalThisNum % 10;
           rev = rev * 10 + dig;
           evalThisNum = evalThisNum / 10;

          }

           if (n == rev) {

               isItPalin=true;
           }

           return isItPalin;

    }


    public static void main(String args[]) throws java.lang.Exception{

        BufferedReader r1 = new BufferedReader(new InputStreamReader(System.in));

        /*BufferedReader r1 = new BufferedReader (new FileReader(new File ("C:\\Documents and Settings\\Administrator\\My Documents\\NetBeansProjects\\Sphere\\src\\sphere\\sphere\\PALIN_INPUT.txt")));*/

        String read = r1.readLine();

        int numberOfTestCases = Integer.parseInt(read);

        for (int i=0; i<numberOfTestCases;i++){

        read = r1.readLine();

        if (read!=null){

        int num = Integer.parseInt(read);

        System.out.println(firstPalinLargerThanNum(num));

        }
        }
    }


}

Input:

2
808
2133

line 73 is: int num = Integer.parseInt(read);

Answer 1

You will get that error if you hit <Enter> when the program is expecting a number.

Suppose your input is

2
3 
<Enter>

You will receive the error you have indicated after processing the number 3, as you have told your routine to iterate twice.

As an aside, on top of error handling around the number parsing, you might also want to introduce a trim() to the readLine() method calls:

String read = r1.readLine().trim();

This will allow you to handle gracefully the input in the event that the user to put in whitespace around the numbers.