Why do I fail the test?

Question about the task

Splitting a file

Java Core, Level 8, Lesson 5

Resolved

The output is correct but fail condition 2 and 3.

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; /* Splitting a file */ import java.io.*; import java.util.ArrayList; public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String file1 = reader.readLine(); String file2 = reader.readLine(); String file3 = reader.readLine(); FileInputStream fileName1 = new FileInputStream(file1); FileOutputStream fileName2 = new FileOutputStream(file2); FileOutputStream fileName3 = new FileOutputStream(file3); byte[] buffer = new byte[fileName1.available()]; while(fileName1.available() > 0){ int count = fileName1.read(buffer); int mid = count % 2 == 0 ? count / 2 : (count + 1 ) / 2 ; fileName2.write(buffer, 0, mid); fileName3.write(buffer, (mid + 1), count); } reader.close(); fileName1.close(); fileName2.close(); fileName3.close(); } }

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Mateusz

Level 31 , Gdańsk, Poland

2 January 2021, 16:29

solution

move lines 24-27 out of the while loop and try

fileName3.write(buffer, mid, count - mid);

Liliane Top Backend Developer at Procura

2 January 2021, 16:55

I removed the while loop. But I do not understand you line of code: fileName3.write(buffer, start, end) I thought I'm writing all the bytes from the buffer starting in mid and ending at end which is count. Why do you suggest I end with count-mid which is the mid? The start and end value of the write method is the part we want to write from the buffer, or do I misunderstand that?

Liliane Top Backend Developer at Procura

2 January 2021, 17:10

solution

I looked into it and my understanding is now as follows: fileOutputStream.write(fileInputStream, int from, int length) so the first parameter is the fileInputStream from where we reading which is a byte[]. The second parameter is from which byte we start reading en the third is NOT the end of the byte[] but the length. So how many bytes we will be writing to the fileOutputStream. That was my misunderstanding!

Mateusz

Level 31 , Gdańsk, Poland

2 January 2021, 17:18

Don't worry, I had same problem with this task :)

Liliane Top Backend Developer at Procura

2 January 2021, 18:42

Some are really confusing but always so happy when I pass the test 🥳

Nouser

Level 36 , Germany

2 January 2021, 15:55

write(byte[], start, end)... start is inclusive, end exclusive. If mid is eg 1000 then you write to the file 2 bytes 0 - 999 and to file 3 1001 to end

Liliane Top Backend Developer at Procura

2 January 2021, 16:05

I changed it to: fileName2.write(buffer, 0, (mid + 1)); fileName3.write(buffer, (mid + 1), count); still fail....

Liliane Top Backend Developer at Procura

2 January 2021, 16:08

also tried: fileName2.write(buffer, 0, (mid + 1)); fileName3.write(buffer, (mid + 2), count); I'm flabbergasted why this is not passing the test.

Nouser

Level 36 , Germany

2 January 2021, 17:28

solution

try

fileName2.write(buffer, 0, mid);
fileName3.write(buffer, mid, count / 2);

The first parameter is not a stream but a byte array. Before you used an inputStream to read the contents of a file into that byte array. The second parameter is the start index, from where in the byte array to read and then to write into the output stream. The last parameter is the length it should write. Example: your file has a length of 1000 bytes. To each file the half should be written (500 bytes). The indexes of the byte array range from 0 to 999, the first file from 0 to 499, so start is 0, length 500 the second from 500 to 999, start 500, 500.

fileName2.write(buffer, 0, 500); //500 is excluding, so it's writing bytes 0 to 499
fileName3.write(buffer, 500, 500);

try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
     FileInputStream in = new FileInputStream(reader.readLine());
     FileOutputStream out1 = new FileOutputStream(reader.readLine());
     FileOutputStream out2 = new FileOutputStream(reader.readLine())) {

    int length = in.available();
    byte[] buffer = new byte[length];
    if (length > 0) {
        int mid = (length + 1) / 2;

        in.read(buffer);
        out1.write(buffer, 0, mid);
        out2.write(buffer, mid, length / 2);
    }
} catch (IOException e) {
    e.printStackTrace();
}