I/O code exception

[gurneeraj singh]

  import java.io.*;
 
class Test {
  public static void main( String args[ ]) throws IOException {
 
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String s=in.readLine();
 
    File f=new File("c:\\dog.txt");
    FileWriter fw=new FileWriter(f);
    fw.write(s);
    fw.flush();
    fw.close();
 
    char[] o=new char[50];
 
    FileReader fr=new FileReader(f);
    fr.read(o);
    fr.close();
 
    String str= new String(o);
    System.out.println(str);
    int i=Integer.parseInt(str); //-------->Line 1
    System.out.println(2*i);
 
 }
}  

If we run the above code by typing a integer value say 3 it produces NumberFormatException in Line 1. Why?
When we know that string "3" can be changed into integer value 3 by parseInt() method without any exception.

[ March 26, 2008: Message edited by: gurneeraj singh ]

[Ulf Dittmer]

What is the value of "str" when parseInt is called?

[gurneeraj singh]

value of str was 3 when parseInt was called

[Ulf Dittmer]

Just a single character? No white space around it? That would sound like a bug.

[gurneeraj singh]

yes, just a single chracter "3" no white space. Line just above Line 1 prints 3 but when we use parseInt it throws exception.

[gurneeraj singh]

Thanks Ulf,
Acctually I got the answer from your reply, there is whitespace with string str because of the empty char array elements when converted to string str. There are two ways to get rid of this
1) Use str=str.trim(); just above the Line 1
2) Or set the char array size to 1.
[ March 26, 2008: Message edited by: gurneeraj singh ]

[Deepak Chopra]

Hi. Tell you the way to test String value in a program..!!
always try to print String value like this
System.out.println("["+ str + "]");
so Atmost you know whether string was blank,containing space etc..!!

[Ben Souther]

Originally posted by gurneeraj singh:
... 2) Or set the char array size to 1.

What if the user types '33'?

[gurneeraj singh]

Dear Ben,
You are right so we have to opt first option i.e. to use trim method.

[gurneeraj singh]

I think sunny's method is also good to check whether string has whitespace or not

[gurneeraj singh]

   import java.io.*;
class Test {
 public static void main( String args[ ]) throws IOException {
 
   BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
   String s=in.readLine();
 
   int n=s.length(); //------ Line a1
   
   File f=new File("c:\\dog.txt");
   FileWriter fw=new FileWriter(f);
   fw.write(s);
   fw.flush();
   fw.close();
   
   char[] o=new char[n]; //------ Line a2
 
   
   FileReader fr=new FileReader(f);
   fr.read(o);
   fr.close();
   String str= new String(o);
   i=Integer.parseInt(str);  //-------->Line 1
   System.out.println(2*i);
 }
} 

Dear Ben,
I think if we make following changes to code at line a1 & line a2. We are somewhat able to solve the problem of exception at line 1. Please suggest!