Getting a NumberFormatException

问题:

I was writing some code for an interviewstreet.com challenge My code gives a NumberFormatException

import java.io.*;

public class BlindPassenger
{
  public static void main(String [] args) throws IOException
  {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String line = br.readLine();
    int t,n;
    //System.out.println(line);
    t = Integer.parseInt(line);
    for(int i=0;i<t;++i)
    {
      line = br.readLine();
      n = Integer.parseInt(line); --n;
      if(n == 0)
      {
        System.out.println("poor conductor");
      }
      else
      {
        char direction='l',seat_posn='l';
        int row_no = 0, relative_seat_no = 0;
        row_no = (int) Math.ceil(n/5.0);
        relative_seat_no = n % 5;
        if(row_no % 2 == 0)
        {
          //even row, need to reverse the relative seat no
          relative_seat_no = 6 - relative_seat_no;
        }

        if(relative_seat_no < 3)
        {
          direction = 'L';
          if(relative_seat_no == 1) seat_posn = 'W';
          else seat_posn = 'A';
        }
        else
        {
          direction = 'R';
          if(relative_seat_no == 3) seat_posn = 'A';
          else if(relative_seat_no == 4) seat_posn = 'M';
          else seat_posn = 'W';
        }

        System.out.println(row_no + " " + seat_posn + " " + direction);
      }
    }
  }
}

Here is the test case that they use

3 
1 
2 
3 

Output: 
poor conductor 
1 W L 
1 A L

There seems to be a trailing space or something at the end of each line that causes the exception.

$ java BlindPassenger <input00.txt
Exception in thread "main" java.lang.NumberFormatException: For input string: "3
 "
        at java.lang.NumberFormatException.forInputString(NumberFormatException.
java:65)
        at java.lang.Integer.parseInt(Integer.java:492)
        at java.lang.Integer.parseInt(Integer.java:527)
        at BlindPassenger.main(BlindPassenger.java:11)

This has taken up half an hour and I don't know how to fix this. Kills the fun of the event doesn't it. Can someone tell me what I'm doing wrong.

回答1:

Integer.parseInt() can't handle strings that don't fit its expected format, as you've found out. You could trim() the string before you parse it:

t = Integer.parseInt(line.trim());

This gets rid of leading and trailing whitespace.

回答2:

You have to trim the string

import java.io.*;

public class BlindPassenger
{


    public static boolean isEmpty(final String string)  
            {  
               return string == null  || string.trim().isEmpty();  
            }  
  public static void main(String [] args) throws IOException
  {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String line = br.readLine();
    int t,n=0;
    //System.out.println(line);
    t = Integer.parseInt(line);
    for(int i=0;i<t;++i)
    {
      line = br.readLine();

     if(!isEmpty(line)){
      n = Integer.parseInt(line.trim());
      --n;
     }

      if(n == 0)
      {
        System.out.println("poor conductor");
      }
      else
      {
        char direction='l',seat_posn='l';
        int row_no = 0, relative_seat_no = 0;
        row_no = (int) Math.ceil(n/5.0);
        relative_seat_no = n % 5;
        if(row_no % 2 == 0)
        {
          //even row, need to reverse the relative seat no
          relative_seat_no = 6 - relative_seat_no;
        }

        if(relative_seat_no < 3)
        {
          direction = 'L';
          if(relative_seat_no == 1) seat_posn = 'W';
          else seat_posn = 'A';
        }
        else
        {
          direction = 'R';
          if(relative_seat_no == 3) seat_posn = 'A';
          else if(relative_seat_no == 4) seat_posn = 'M';
          else seat_posn = 'W';
        }

        System.out.println(row_no + " " + seat_posn + " " + direction);
      }
    }
  }
}