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Keep getting the following mentor recommendation: When there is an odd number of bytes in the first file, your program writes the smaller half of the bytes. It should write the larger half. When there is an odd number of bytes in the first file, your program writes the larger half to the third file. It should write the smaller half. I've tried all combinations of +1/-1/+2 etc in lines 29/30 and 32/33 - nothing works

Read 3 file names from the console: file1, file2, file3.
Split file1 as follows:
Write the first half of its bytes to file2,and write the second half of its bytes to file3.
If the number of bytes in file1 is odd, then file2 should contain the larger half.
Close the streams.

Requirements:

The program should read a file name three times from the console.
Use FileInputStream to read from a file, and use FileOutputStream to write to files.
The first half of the bytes in the first file must be written to the second file.
The second half of the bytes in the first file must be written to the third file.
The FileInputStream and FileOutputStream must be closed.

package com.codegym.task.task18.task1808; import java.io.*; /* Splitting a file */ public class Solution { public static void main(String[] args) throws Exception{ BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String file1 = reader.readLine(); String file2 = reader.readLine(); String file3 = reader.readLine(); FileInputStream fileReader1 = new FileInputStream(file1); FileOutputStream fileWriter2 = new FileOutputStream(file2); FileOutputStream fileWriter3 = new FileOutputStream(file3); byte[] buffer = new byte[fileReader1.available()]; int count = 0; while (fileReader1.available()>0){ count += fileReader1.read(buffer); } if (count%2==0){ fileWriter2.write(buffer,0,(count/2)-1); fileWriter3.write(buffer,((count/2)),count); }else{ fileWriter2.write(buffer,0,((count/2)+1)); fileWriter3.write(buffer,((count/2)+2),count); } fileReader1.close(); fileWriter2.close(); fileWriter3.close(); } }

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jonathan D

Level 26 , Lille, France

9 January 2020, 09:20

The problem is the length of the third argument and the offset when you call write(). Let's admit you have 5 bytes in file 1, you reach your else and call => fileWriter2.write(buffer,0,((count/2)+1)) then you write from the byte at the offset 0 from your buffer with a length of 3 (5/2 + 1) After you call => fileWriter3.write(buffer,((count/2)+2),count) then you write from the byte at the offset 4 (5/2 + 2) from your buffer with a length of 5. (4 + 5) => IndexOutOfBoundsException. And the 4th byte is not treated. You should simply check if the number is odd (count/2 + 1) or even (count + 2) in order to define the offset and subtract it from count in your 3rd argument, for this example: else{ fileWriter2.write(buffer, 0, count/2+1); fileWriter3.write(buffer, count/2+1, count - (count/2+1)); }

Anthony Chalk

Level 30 , London, United Kingdom

9 January 2020, 10:04

I'm sorry I don't understand. I changed my code to:

if (count%2==0){
    fileWriter2.write(buffer,0,(count/2));
    fileWriter3.write(buffer,((count/2)),count);
}else{
    fileWriter2.write(buffer, 0, count/2+1);
    fileWriter3.write(buffer, count/2+1, count - (count/2+1));
}

and it's still failing

jonathan D

Level 26 , Lille, France

9 January 2020, 10:11

solution

It's normal you didn't adapt the if block, try this I think it should be ok:

if (count%2==0){
            fileWriter2.write(buffer,0,count/2);
            fileWriter3.write(buffer,count/2,count - count/2);
        }else{
            fileWriter2.write(buffer,0,count/2+1);
            fileWriter3.write(buffer,count/2+1,count - (count/2+1));
        }

Anthony Chalk

Level 30 , London, United Kingdom

9 January 2020, 10:50

Thank you very much. I'm still unclear though, why it should be count - count/2 and count - (count/2+1) From what I understood, that argument determines the index in the buffer where it should stop writing i.e. if the buffer is 10 elements in length:

write(buffer,0,6);

would write from the 0 element to the 6th element so:

write(buffer,count/2,count - count/2);

would write from half-way through the buffer to half-way through the buffer? Edit: having looked at the documentation, it actually seems that for: public void write(byte[] b, int off, int len) len determines the amount of bytes to be written, not the index in the buffer

jonathan D

Level 26 , Lille, France

9 January 2020, 12:08

useful

Yes this is the reason that made me talking about length for the 3rd argument. Let's take an example, in file 1 we have the word "hello". If 1 letter = 1 byte: length = 5 According to the task we need to determine whether there is an even or odd number of letters and put the larger half in file2. In our case the number of bytes is 5 so we have to put 3 of them in file2 and 2 in file3 5/2 + 1 => 3 this allows us to find the larger half for the file 2 (count/2 + 1) then :

fileWriter2.write(buffer, 0, count/2+1);

will write, for our example, "hel" => 3 bytes (3rd argument in write() , from the offset 0 => 2nd argument) After that there are 2 bytes remaining ("lo"), we first need to adapt the offset to start from the right position (2nd arg in write() and adapt le length/amount of bytes remaining => 3rd argument):

fileWriter3.write(buffer, count/2+1, count - (count/2+1));

In our case it's equivalent to:

fileWriter3.write(buffer, 3 , 2);

From the offset 3 we write 2 bytes ("lo") If the number of bytes is even we just have to spit them in 2 equal parts, then we must use count/2

Anthony Chalk

Level 30 , London, United Kingdom

9 January 2020, 12:43

Thank you very much for explaining it to me