CodeGym/Help with Java Tasks/What am I doing wrong?

Level 32

Budapest

03.09.2024
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10comments

What am I doing wrong?

Question about the task

Resolved

My code is supposed to read several file names from the console until the "end", sort them by the number that follows the "part" word in the name (tried to do so with the help of my Sorter class), create a file in the same directory and name it the same way as the other files, just without "partN", and then copy the data from the read files to the one I created. According to my logic, I did all of that, while the validator doesn't agree with me at all:(. I wonder what I'm missing here.

Let's build a file from various pieces.
Read file names from the console.
Each file has a name: <someName>.partN.

For example, Lion.avi.part1, Lion.avi.part2, ..., Lion.avi.part37.

The file names are supplied in random order. The word "end" is used to stop reading in file names.
In the folder where all the files are located, create a file without the "part" suffix, i.e. without ".<partN>".

For example, Lion.avi.

Use a buffer to copy all the bytes from the partial files to the created file.
Copy the first in the proper order, first the first part, then the second, ..., finally - the last part.
Close the streams.

Requirements:

The program must read file names from the console until the word "end" is entered.
Create a stream to write to the file without the "part" suffix (".<partN>") in the folder with all the "part" files.
Copy all the bytes from the *.partN files to the new file.
You should use a buffer for the reading and writing.
The file streams must be closed.
Don't use static variables.

package com.codegym.task.task18.task1825; import java.io.*; import java.util.*; import java.util.stream.Collectors; import java.util.stream.Stream; /* Building a file */ public class Solution { public static void main(String[] args) throws IOException, IndexOutOfBoundsException { //• The program must read file names from the console until the word "end" is entered. - OK BufferedReader breader = new BufferedReader(new InputStreamReader(System.in)); TreeSet<String> fileNames = new TreeSet<String>(new Sorter()); String fileName = null; while (breader.ready()) { fileName = breader.readLine(); fileNames.add(fileName); if (fileName.equalsIgnoreCase("end")) break; } //find out the name of the folder where the files are stored (one file's location is enough, I guess?) File file = new File(fileName); File directory = file.getParentFile(); String directoryName = directory.getAbsolutePath(); //create a file in that directory under the name of any of the other files, just without "partN" String[] fileNameSplit = fileName.split("part"); String targetFileName = fileNameSplit[0]; File targetFile = new File(directoryName, targetFileName); //• Create a stream to write to the file without the "part" suffix (".<partN>") // in the folder with all the "part" files. - NOT ACCEPTED BY THE VALIDATOR FileOutputStream outputStream = new FileOutputStream(targetFileName); //or is it better to use targetFile.getAbsolutePath()? //• Copy all the bytes from the *.partN files to the new file. - NOT ACCEPTED BY THE VALIDATOR //• You should use a buffer for the reading and writing. - I THOUGHT byte[] byteArray WAS A BUFFER... for (String fn : fileNames) { FileInputStream inputStream = new FileInputStream(fn); byte[] byteArray = new byte[inputStream.available()]; inputStream.read(byteArray); outputStream.write(byteArray); inputStream.close(); //each input stream is closed inside the loop } //• The file streams must be closed. - NOT ACCEPTED, AS "NOT ALL FILE INPUT STREAMS WERE CLOSE" (but I closed them inside the loop above) breader.close(); outputStream.close(); //• Don't use static variables. - OK } public static class Sorter implements Comparator<String> { @Override public int compare(String s1, String s2) { int n1 = Integer.parseInt(s1.split("part")[1]); int n2 = Integer.parseInt(s2.split("part")[1]); return n2 - n1; } } }

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Pavel281185 Backend Developer

3 September, 11:21

Change

while (breader.ready())

for

while (true)

It is impossible to have breader ready immediately after starting program because it is return null.

Evgeniia Shabaeva

Level 32 , Budapest, Hungary

3 September, 13:10

Wow, I didn't know that, thank you. So, when does the buffered reader become ready then (if not immediately)? The thing is, I'm not the one entering information, I'm just reading it from the console.

Thomas

Level 41 , Bayreuth, Germany

3 September, 10:21

Your program throws exceptions. That's cause reading strings does not work that way (breader.ready()). The buffer of your buffered reader is empty, you didn't enter something right after starting the program... that means --> false, no input loop. filename is null, new File(fileName) --> NullPointerException

Evgeniia Shabaeva

Level 32 , Budapest, Hungary

3 September, 13:17

Thank you very much, Thomas! Do you see any other problems in the code? 'Cos I don't think it's the only one) Btw, how could I enter something right after starting the program? Do we usually do it?

Thomas

Level 41 , Bayreuth, Germany

3 September, 14:27

There are a few things that may be a problem - Sorting is desc not asc - depending on how you fixed your filenames loop it may be that the last 'fileName' is the String 'end' and that you use to determine the target file - even if you do not use 'end' it looks fishy to me. Splitting by part will probably leave a dot at the end of [0] of the resulting array. Also you mess with directory name and compose smth. But imho you input an absolute path like c:\Temp\lion.avi.part1 Let's assume you use fileName.substring(0, fileName.lastIndxOf('.')); then the result is c:\Temp\lion.avi and you don't have to do any more path construction work. I recommend getting used to try-with-resources. That makes in-out streams a lot easier (and later nio of course).

try (BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFileName))) {
    for (String file : fileNames) {
        try (InputStream in = new BufferedInputStream(new FileInputStream(file))) {

        }
    }
} catch (IOException ioe) {
    throw new UncheckedIOException(ioe);
}

Guadalupe Gagnon

Level 37 , Tampa, United States

4 September, 13:22

Thomas has great advice as always. One thing I would like to add about splitting by "part": what if the directory had folders along its path with the partial String "part"? Take for example: C:\party\partner\partition\part\lion.avi.part3 If you split that by "part" you end up with this Array: ["C:\", "y\", "ner\", "ition\", "\lion.avi.", "3"] *Hint* If you look at the task conditions it guarantees that .partN will be a part of the file path, and at the very end. Thomas suggested using substring with lastIndexof('.') to get the file name. To get the number I suggest using substring with lastIndexof('t') to find get the part number. If you choose to do so I will leave the rest of that implementation up to you. Of course you could always split by ".part" instead of simply "part" if you don't want reimagine the algorithm you came up with.

Evgeniia Shabaeva

Level 32 , Budapest, Hungary

12 September, 09:09

Thank you very much, Thomas, I really wrote something too long to create a file in the same directory, while it was enough to just shorten the name of any other file read from the console. Now my code is shorter and finally meets the requirements. By the way, I also had to move the finding out of the target file's name into the while loop (to pass the second requirement). I'm not quite sure why it couldn't work outside the loop, but OK. The comment that I was leaving a dot in the file name was really valuable, thank you.

Evgeniia Shabaeva

Level 32 , Budapest, Hungary

12 September, 09:11

Thank you, Guadalupe, I also thought of splitting the strings by ".part", as I definitely didn't need to keep those dots. Your explanation of how an array made of a different file name would work came really valuable.

Thomas

Level 41 , Bayreuth, Germany

12 September, 10:31

By the way, I also had to move the finding out of the target file's name into the while loop (to pass the second requirement). I'm not quite sure why it couldn't work outside the loop, but OK. Depending on your coding you may leave the while loop with the String fileName initialized to "end" (but works with your way, too, I just like using the loop condition extensively more ;) ). So you either would need to check for 'end' in the loops condition and in addition to that use a second String variable that holds a valid path

String fileName = null, basePath = null;
while (breader.ready()) {
    ...
    if (...) break;
    basePath= fileName;
}

alternative coding:

String basePath = null;
for (String path; !"end".equals(path = console.readLine());) {
    basePath = path;

    ...
}

or you check later if the list is not empty and then grab the first entry.

while (breader.ready()) {
    ...
    fileNames.add(fileName);
    ...
}

if (fileNames.isEmpty())
    throw new RuntimeException("no parts to join");

fileNames.first().substring(...)

Evgeniia Shabaeva

Level 32 , Budapest, Hungary

16 September, 10:04

Thank you very much, Thomas!