Where do the extra lines come from?

Question about the task

Reversing a file

Java Core, Level 8, Lesson 5

Resolved

I did the task and it's valid, but i tested my code and got this question now: My fileinput was:

Start
hi, this is a test.
how are you?
thank you for visiting
blank
blank
blank

end.

But when i checked outcome in the textfile it was:

.dne


knalb

knalb

knalb

gnitisiv rof uoy knaht

?uoy era woh

.tset a si siht ,ih

tratS

So it worked, but there are additional line breaks (not one extra per line break tho, there would be one missing before ".dne"). Oddly enough when i red the destination file via FileInputStream to the console the output was as should be: reversed without extra line breaks. Why is this, and why does it look different in the file than from what the FileInputStream reads? Thanks for answering.

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Guadalupe Gagnon

Level 37 , Tampa, United States

9 December 2020, 16:40

Can't answer without seeing your code

MoJo

Level 18 , Cairns, Australia

Expert

9 December 2020, 17:45

package com.codegym.task.task18.task1809;

/*
Reversing a file

*/

import java.io.*;

public class Solution {
    public static void main(String[] args) throws IOException {

        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        String file1 = bf.readLine();
        String file2 = bf.readLine();
        bf.close();

        FileInputStream fis = new FileInputStream(file1);
        FileOutputStream fos = new FileOutputStream(file2);

        byte[] buffer = new byte[fis.available()];

        while (fis.available() >0)
        {
            fis.read(buffer);
        }

       // System.out.println(buffer.toString());

        fis.close();

        for(int i = buffer.length-1; i >= 0; i--){                          //there's an extra line on lines brake all the time
                                                                            //there's an extra line on lines brake all the time
            fos.write(buffer[i]);                                           //there's an extra line on lines brake all the time
        }                                                                   //there's an extra line on lines brake all the time
                                                                            //there's an extra line on lines brake all the time
        fos.close();

    //   fis = new FileInputStream(file2);

    //   String s ="";

    //   while (fis.available()>0){
    //       s+= (char)fis.read();
    //   }
    //   System.out.print(s);



    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 December 2020, 14:30

solution

Sorry for the delay. After doing some research I found that different operating systems use different ways of ending a line. In the windows environment you will have a carriage return followed by a new line (this would be byte 13 followed by byte 10, or "/r/n"). The carriage return is a legacy item that still holds over today from the first computers that interfaced with typewriters. MacOS used to use the carriage return as its standard, but has switched to new line. Link to more reading on this When you read a txt file in windows you are going to get the standard CR LF (carriage return line feed) each new line. When the bytes are reversed it also reverses those two and windows handles it differently... by adding an additional space. It actually does some weird things depending on if you have CRLF, LF, CR, or LFCR. Here is a quick program for you to run and consider:

Guadalupe Gagnon

Level 37 , Tampa, United States

10 December 2020, 14:30

public static void main(String[] args) throws IOException {
   // a string with different CR(\r) and LF(\n) configurations
   String x = "Only a\r\nprogrammer\rcould figure\n\rthis\nout";

   // this outputs the raw bytes to console
   System.out.println("The String 'x' in raw bytes:");
   System.out.println(Arrays.toString(x.getBytes()));

   //this outputs the string in the way java handles it
   System.out.println("\nThe String 'x' as compiled by the Java compiler");
   System.out.println(x);

   // enter a txt file on your computer here to compare the output to Java's output above
   // this will output the string how your OS would handle it
   new FileOutputStream("Enter_a_path_to_a_file_on_your_system_here").write(x.getBytes());
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 December 2020, 14:33

Also, thanks for sharing this question. I was unaware about this and had to do research to get to this answer. I learned something new!!

Misiu

Level 41 , Gdansk, Poland

10 December 2020, 15:00

Strange things with these 13, 10. Thank you GG :)

MoJo

Level 18 , Cairns, Australia

Expert

14 December 2020, 11:30

Thanks for the extra lesson. "Also, thanks for sharing this question. I was unaware about this and had to do research to get to this answer. I learned something new!!" -> means a lot form you, thank you.

Guadalupe Gagnon

Level 37 , Tampa, United States

14 December 2020, 14:26

We are all learning =)