CodeGym/Help with Java Tasks/Where is the problem? NOT SOLVED!

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30.04.2021
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Where is the problem? NOT SOLVED!

Question about the task

Building a file

Java Core, Level 8, Lesson 11

Resolved

I have been tested with different path and folders - all ok!

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.nio.file.Path; import java.nio.file.Paths; import java.util.*; import java.util.regex.Matcher; import java.util.regex.Pattern; /* Building a file */ public class Solution { public static void main(String[] args) throws IOException { Scanner sc = new Scanner(System.in); ArrayList<File> ar = new ArrayList<>(); while (true) { String s = sc.nextLine(); if (s.equals("end")) break; File f = new File(s); ar.add(f); } sc.close(); Collections.sort(ar); Path p = Paths.get(ar.get(0).getAbsolutePath()); String fname = String.valueOf(p.getFileName()); String[] sa = fname.split("\\.part\\d+"); File test = new File(String.valueOf(p)); FileOutputStream results = new FileOutputStream(p.getParent() + "\\" + sa[0] + "." + getFileExtension(test)); for (File d : ar) { FileInputStream i = new FileInputStream(d); while (i.available()>0) { int data = i.read(); results.write(data); } i.close(); } results.close(); } public static String getFileExtension(File file) { String fileName = file.getName(); if (fileName.lastIndexOf(".") != -1 && fileName.lastIndexOf(".") != 0) return fileName.substring(fileName.lastIndexOf(".")+1); else return ""; } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

30 April 2021, 16:11

solution

Sorting is going to be alphabetic, this does not work for numbers. The results would end up something like this: ...part1 ...part10 ...part11 ...part12 ...part2 ...part3 ...part4 ...part5 ...part6 ...part7 ...part8 ...part9 Also, lines 29-32 don't seem to do anything. I think you mean to use one of the values in the String array 'sa'.

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 10:05

thank you so much! 😀 sorry for the delay..

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 11:03

the output did not change - the same requirements

public class Solution {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        HashMap<Integer, File> map = new HashMap<>();

        while (true) {
            String s = sc.nextLine();
            if (s.equals("end")) break;
            File f = new File(s);
            String[] t = s.split("\\.part");
            String[] t1 = t[1].split("\\.");
            int key = Integer.parseInt(t1[0]);
            map.put(key, f);
        }
        sc.close();
        Map<Integer, File> map2 = new TreeMap<>(map);

        File rand = null;
        for (File obj : map.values()) {
            rand = obj;
            break;
        }

        String fname = rand.getName();
        String[] sa = fname.split("\\.part\\d+");
        FileOutputStream results = new FileOutputStream(rand.getParent() + "\\" + sa[0] + "." + getFileExtension(rand));


        for (Map.Entry entry : map2.entrySet()) {
            FileInputStream i = new FileInputStream((File) entry.getValue());
            while (i.available()>0) {
                int data = i.read();
                results.write(data);
            }
            i.close();
        }
    }

    public static String getFileExtension(File file) {
        String fileName = file.getName();
        if (fileName.lastIndexOf(".") != -1 && fileName.lastIndexOf(".") != 0)
            return fileName.substring(fileName.lastIndexOf(".")+1);
        else return "";
    }
}

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 12:50

useful

A few hints: 1. line 4, make that a TreeMap from the beginning, then you do not need line 16 and a second map. 2. and make the reference variable a TreeMap as well, then you can use treemaps additional methods like

String firstFileÍnMap = map.firstEntry().getValue().getAbsolutePath();
File outputFile = new File(firstFileÍnMap.substring(0, firstFileÍnMap.lastIndexOf(".")));

then don't need lines 18 -25 and 39-44 anymore 3. use better variable names like out and in for the streams like

FileOutputStream out = new FileOutputStream(outputFile);

4. use generics, that way you do not need to cast the map keys and values to their original type like

for (Map.Entry<Integer, File> entry : map.entrySet()) {
    FileInputStream in = new FileInputStream(entry.getValue());
    while (in.available() > 0) {
        out.write(in.read());
    }
    in.close();
}

5. don't forget to close the output stream after your last for each loop 6. oh, and String[] t1 = t[1].split("\\."); isn't necessary as it does nothing. t[1] already contains the key

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 13:05

thank you, very helpful! remove the big part of code) you are the best! but still not pass verification...

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 13:06

what's your actual code now and which requirements fail? Do not just use an Input- and OutputStreamReader but either wrap it in buffered readers or use a byte array buffer (if you not already did that). Then it should validate.

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 13:11

I founded some mistakes right now: 1. my program create just file, not .txt extension; 2. String[] t1 = t[1].split("\\.") still needed, t[1] is "N.txt", I suppose the order of the key is important for data reading waiting for your reply! =)

public class Solution {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        TreeMap<Integer, File> map = new TreeMap<>();

        while (true) {
            String s = sc.nextLine();
            if (s.equals("end")) break;
            File f = new File(s);
            String[] t = s.split("\\.part");
            String[] t1 = t[1].split("\\.");
            int key = Integer.parseInt(t1[0]);
            map.put(key, f);
        }
        sc.close();

        String firstFile = map.firstEntry().getValue().getAbsolutePath();
        File outputFile = new File(firstFile.substring(0, firstFile.lastIndexOf(".")));

        FileOutputStream out = new FileOutputStream(outputFile);

        for (Map.Entry entry : map.entrySet()) {
            FileInputStream in = new FileInputStream((File) entry.getValue());
            while (in.available()>0) {
                out.write(in.read());
            }
            in.close();
        }
        out.close();
    }
}

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 13:17

don't think so, you have parts like test.avi.part1, and with .part you split that in [0] test.avi and [1] 1 So this works perfect (btw, you could save the output file name here as well and won't have later the need to do that). Add the buffer as mentioned above. I'll test your code now.

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 13:22

Works smooth for me ;) here the version with buffered streams:

public class Solution {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        TreeMap<Integer, File> map = new TreeMap<>();

        String fileName;
        while (!(fileName = sc.nextLine()).equals("end")) {
            map.put(Integer.parseInt(fileName.replaceAll("\\D", "")), new File(fileName));
        }
        sc.close();

        String firstFile = map.firstEntry().getValue().getAbsolutePath();
        File outputFile = new File(firstFile.substring(0, firstFile.lastIndexOf(".")));

        try(BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outputFile))) {
            for (Map.Entry<Integer, File> entry : map.entrySet()) {
                try(BufferedInputStream in = new BufferedInputStream(new FileInputStream(entry.getValue()))) {
                    while (in.available() > 0) {
                        out.write(in.read());
                    }
                } catch (IOException ioe) { /* ignore */ }
            }
        } catch (IOException ioe) { /* ignore */ }
    }
}

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 14:17

I have been tested your code and it's not work correct. maybe i am missed something.. but it created new file with ".part" prefix, why?

I suppose this:

File outputFile = new File(firstFile.substring(0, firstFile.lastIndexOf(".part")) + ".txt");

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 14:18

and this file have not .txt... just some file i use these files as input: C:\L\Lion.avi.part11.txt C:\L\Lion.avi.part3.txt C:\L\Lion.avi.part1.txt C:\L\Lion.avi.part2.txt end

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 14:58

With .txt at the end it of course won't work as you may expect it cause the code just removes everything after and including the last dot. However the task asks for part files like: For example, Lion.avi.part1, Lion.avi.part2, ..., Lion.avi.part37. and that's what you need to use.. I used here eg. c:\Temp\test.avi.part1 c:\Temp\test.avi.part17 c:\Temp\test.avi.part2 not another txt extension is asked for. The output should be c:\Temp\test.avi I added the following content to the parts c:\Temp\test.avi.part1 1 c:\Temp\test.avi.part17 17 c:\Temp\test.avi.part2 -2- after running the code I get the expected c:\Temp\test.avi file containing 1-2-17 pretty perfect :) For easier editing you also can use files like c:\Temp\test.txt.part1. Then you get of course a c:\Temp\test.txt result. So what does Codegym still complain about? And have you tried to reset the task already?

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 15:06

That's my first solution and it validated:

TreeMap<Integer, String> map = new TreeMap<>();
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String fileName;
//TreeSet sorts strings alphabetically, so 11 comes before 2, like 1,11,111,2,3,4,5... I didn't want to
//use Collections comparator so I went for the map solution, getting the number after the partxxx, and use that as key
while (!(fileName = reader.readLine()).equals("end")) {
    map.put(Integer.parseInt(fileName.replaceAll("\\D", "")), fileName);
}
reader.close();
//calculate the output filename (substring (0 - last occurance [lastIndexOf()] of '.'))
String firstFileName = map.firstEntry().getValue();
String outFileName = firstFileName.substring(0, firstFileName.lastIndexOf('.'));

FileOutputStream out = new FileOutputStream(outFileName);
FileInputStream in;

//loop through map and read all filenames in map and save to output stream
for (Map.Entry<Integer, String> pair : map.entrySet()) {
    in = new FileInputStream(pair.getValue());
    byte[] buffer = new byte[1024];

    while (in.available() > 0) {
    int byteCount = in.read(buffer);
    out.write(buffer, 0, byteCount);
    }
    in.close();
}
out.close();

Later I validated that task using a TreeSet. But that solution I modified later so I do not know if CG accepts it.

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 15:06

public static void main(String[] args) {
    TreeSet<String> set = new TreeSet<>(Comparator.comparing(String::length).thenComparing((o1, o2) -> o1.compareTo(o2)));

    try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
        String fileName = null;
        while (!(fileName = reader.readLine()).equals("end"))
            set.add(fileName);
    } catch (IOException ioe) {  }

    //calculate the output file name, open output stream
    String outputFileName = set.first().substring(0, set.first().lastIndexOf("."));

    try (BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outputFileName))) {
        //loop through the set, read and write
        for (String inputFileName : set) {
            try (BufferedInputStream in = new BufferedInputStream(new FileInputStream(inputFileName))) {
                while (in.available() > 0) out.write(in.read());
            }
        }
    } catch (IOException ioe) {  }

} // end main

Kudos to Guadalupe, the Comparator is based on his idea. My original one used a little bit more code.

Guadalupe Gagnon

Level 37 , Tampa, United States

11 May 2021, 15:29

I don't see anything in your code that would be preventing validation. What are your import statements? If they haven't changed, you should remove the ones that are not being used. If you click one of the greyed out statements in IntelliJ a little light bulb will pop up and you can select "Optimize Imports":

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 15:59

If this message was forward to me, so it did not help ^^ my last version of code:

package com.codegym.task.task18.task1825;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;

/*
Building a file

*/

public class Solution {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        TreeMap<Integer, File> map = new TreeMap<>();

        while (true) {
            String s = sc.nextLine();
            if (s.equals("end")) break;
            File f = new File(s);
            String[] t = s.split("\\.part");
            String[] t1 = t[1].split("\\.");
            int key = Integer.parseInt(t1[0]);
            map.put(key, f);
        }
        sc.close();

        String firstFile = map.firstEntry().getValue().getAbsolutePath();
        File outputFile = new File(firstFile.substring(0, firstFile.lastIndexOf(".part")) + ".txt");

        FileOutputStream out = new FileOutputStream(outputFile);

        for (Map.Entry<Integer, File> entry : map.entrySet()) {
            FileInputStream in = new FileInputStream(entry.getValue());
            while (in.available()>0) {
                out.write(in.read());
            }
            in.close();
        }
        out.close();
    }
}

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 16:02

What if you file name will be with some digits not only after ".partN" prefix? for example "Lion2.avi.part11.txt [UPDATE] all work ok

Thomas

Level 41 , Bayreuth, Germany

11 May 2021, 16:13

Great ;) and additional digits in the filename don't matter at all. Extracting the numbering is just for sorting purposes. If you prefix the ints with a 2 then the sort order is still correct.

Maria

Level 22 , Moscow, Russian Federation

11 May 2021, 17:42

still do not understand why my solution do no pass validation 😬

Thomas

Level 41 , Bayreuth, Germany

13 May 2021, 07:16

useful

Talking about the first solution you posted in the comments I'm to 95% sure it's cause of not using a read/ write buffer (as asked) and not closing the output stream. All other versions still lack the buffer.