File input using FileInputStream does not work properly

Question

The following program should print the String "Humpty Dumpty sat on a wall,\n Humpty Dumpty had a great fall." to a file and input it back.

package io;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;

public class ByteIO {

    /**
     * @param args
     */
    public static void main(String[] args) {
        String output = "Humpty Dumpty sat on a wall,\n Humpty Dumpty had a great fall.";
        System.out.println("Output String : " + output);
        try(PrintStream out = new PrintStream("F:\\Test.txt")) {
            out.println(output);
        } catch(FileNotFoundException e) {
            e.printStackTrace();
        }

        String input = "";
        try(FileInputStream in = new FileInputStream("F:\\Test.txt")) {
            while(in.read() != -1)
                input += (char)in.read();
        } catch(FileNotFoundException e) {
            e.printStackTrace();
        } catch(IOException e) {
            e.printStackTrace();
        }
        System.out.println("Input String : " + input);
    }
}

However, the String I got from the FileInputStream was "upyDmt a nawl, upyDmt a ra al?"! Also, when I opened the file "Test.txt" I found that the output String had become "Humpty Dumpty sat on a wall, Humpty Dumpty had a great fall." in a single line. Where did the \n go?

The \n is there, but maybe your editor won't show it. Regarding your input: your loop is broken insofar as it delivers only every 2nd character. — Ingo
– Ingo, Commented Dec 18, 2012 at 14:29
You should close the file between writing and reading from it. — Peter Lawrey
– Peter Lawrey, Commented Dec 18, 2012 at 14:55
@JavaNewbie always accept the answer, when you got your solution. — Ravi
– Ravi, Commented Dec 19, 2012 at 13:10
@PeterLawrey Not required, because I use try-with-resources : The file is automatically closed at the end of the try block. — JavaNewbie_M107
– JavaNewbie_M107, Commented Dec 19, 2012 at 13:21
@JavaNewbie_M107 Using try-with will solve this. I would catch the exceptions unles syou are going to do something useful with them. If you don't catch teh exception, it will print them out anyway. — Peter Lawrey
– Peter Lawrey, Commented Dec 19, 2012 at 13:46

Hunter McMillen · Accepted Answer · 2012-12-20 15:35:53Z

4

You are calling in.read() twice:

while(in.read() != -1)
    input += (char)in.read();

This reads two characters each iteration instead of one, so you are effectively discarding a character each time.

Try storing the character in the while condition, then just adding that character to input:

EDIT: based on JavaNewbie_M107's comment

int i;    
while((i = in.read()) != -1)
   input += (char)i;

edited Dec 20, 2012 at 15:35

answered Dec 18, 2012 at 14:27

Hunter McMillen

61.8k25 gold badges124 silver badges176 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

JavaNewbie_M107 Over a year ago

The problem with your code is that the char c will never return -1, instead, it will keep returning zero, thus setting an infinite loop.

Hunter McMillen Over a year ago

@JavaNewbie_M107 You are absolutely right, I missed that earlier. I will make an edit.

SJuan76 · Accepted Answer · 2012-12-18 14:28:35Z

1

For the second part, Windows (and many applications like Notepad) do not recognize \n as new line. In Windows, \r\n marks a new line. Try opening with a more serious edit program (WordPad should suffice) and you will see it correctly formatted.

answered Dec 18, 2012 at 14:28

SJuan76

24.9k7 gold badges52 silver badges95 bronze badges

Comments

Ravi · Accepted Answer · 2012-12-18 14:29:30Z

0

As Hunter said, you need to change your code to this

char c;
while((c=in.read()) != -1)
input += c;

answered Dec 18, 2012 at 14:29

Ravi

31.6k44 gold badges124 silver badges180 bronze badges

Comments

JavaNewbie_M107 · Accepted Answer · 2012-12-20 10:58:26Z

0

This is the correct solution to my problem :

int i = 0;
char c;
    do {
        c = (char)i;
        input += c;
        i = in.read();
    } while(i != -1);

The extra space at the front is removed by using a .trim() method.

answered Dec 20, 2012 at 10:58

JavaNewbie_M107

2,0475 gold badges21 silver badges37 bronze badges

Collectives™ on Stack Overflow

File input using FileInputStream does not work properly

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related