Please help....I don't want to copy and paste others' solutions.

Question about the task

Splitting a file

Java Core, Level 8, Lesson 5

Resolved

I think my code is sequentially correct, but I might misunderstand the reading of bytes ?

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.*; public class Solution { public static void main(String[] args) { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String f1 = "",f2="",f3=""; long counter = 0,halfLength = 0; try{ f1 = reader.readLine(); f2 = reader.readLine(); f3 = reader.readLine(); FileInputStream inStream = new FileInputStream(f1); FileOutputStream outStream1 = new FileOutputStream(f2); FileOutputStream outStream2 = new FileOutputStream(f3); File inFile = new File(f1); long fileLength = inFile.length(); if ((fileLength % 2)==0){ //filelength is even number //divide length by 2 to know when to start to write to second file halfLength = (fileLength /2); long i = 0; while (inStream.available()>0){ for (i = 0;i< halfLength;i++){ int n = inStream.read(); outStream1.write(n); } while (inStream.available()>0){ int n = inStream.read(); outStream2.write(n); } } } else{ halfLength = (fileLength /2); halfLength --; long i = 0; while (inStream.available()>0){ for (i = 0;i< halfLength;i++){ int n = inStream.read(); outStream1.write(n); } while (inStream.available()>0){ int n = inStream.read(); outStream2.write(n); } } } reader.close(); inStream.close(); outStream1.close(); outStream2.close(); } catch (Exception e){ } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

3 June 2019, 13:39

So, when the number of bytes is odd, there is definitely a problem with the way you are calculating the split. First, when you divide an integer, any remainder will by truncated. So if the amount of bytes were 7, and you divided by two, you would end up with 3. Your code then subtracts by 1. So for 7, the second file would end up with 2 bytes, and the third file would end up with 5 bytes. The conditions say that the second file (the first one you are writing to) should have the extra byte if the amount of bytes is odd. Rethink the logic of how you split the file. The above should get validation to pass Now for some advice about style: - Always close a stream as soon as you are done using it, not at the end of a program. Streams always are resource intensive and leaving them open longer than needed is can easily create a bottle neck. In your code the reader for user input should be closed at line 21. - I would like to point out that lines 33-44 and 49-60 are EXACT duplicates of each other. When this occurs it is better to figure out a way to get rid of one. In your code you can easily accomplish this by doing the math of figuring out the split before you read/write: if(num % 2 == 0) // math else // odd math // now you can get rid of lines 49-60

Guadalupe Gagnon

Level 37 , Tampa, United States

3 June 2019, 13:48

- the last bit of advice I can offer is that reading and writing 1 byte at a time is very time consuming and resource intensive for the computer. It is exponentially faster to only read 1 time and write 1 time (for each output stream. You can do this with the use of a buffer. The InputStream.available() method returns an int that is the exact length in bytes of the file being read. You can use this to create a byte array that is the exact length that you need. Reading and writing is very easy to do once you get a little practice. The code:

byte[] fullData = new byte[inStream.available()];
int halfLength;
 if ((fullData.length % 2)==0)
 // math for halfLength
else
  // other math for halfLength

FileInputStream inStream = new FileInputStream(f1);
inStream.read(fullData); // this is your magic, reads in everything at once
inStream.close();

FileOutputStream outStream1 = new FileOutputStream(f2);
outStream1.write(fullData,0,halfLength); // see notes below
outStream1.close();

FileOutputStream outStream2 = new FileOutputStream(f3);
outStream2.write(fullData,halfLength,fullData.length);// see notes below
outStream2.close();

So. Those writes are easy to explain. Think of the second and third argument sort of like a for loop, you set i = *first arg* and then loop as long as i < *second arg*. So the first line with "see notes" would look like this: for(int i = 0; i < halfLength; i++) reads from the buffer starting at index 0 and ending when the index is equal to halfLength The second one is exactly the same but starts at halfLength and ends at fullData.length. With this bit of code you can accomplish the read one time then write one time. Later on files do get quite large and you wont be able to read and write all at once, but you can figure the largest chunk the computer can read/write and use that to limit the amount or reads/writes.

Henk

Level 19 , Pretoria, South-Africa

5 June 2019, 06:19

Thanks, it will take a while to learn all the file handling methods with their parameters, especially since every google result does it differently, and it's hopeless to try to look on Stackoverflow, as every programmer there tries to overly "complexify" the situation to sound smarter. I like the buffer reading and writing, thanks for the tip about readers also. Just a question on the way I did it: I used a "long" to divide with %, so should have a remainder ? And yes, the 2 while's are exactly the same, but I assumed the second "while" will continue writing to the 2nd output file where the first "while" stopped (halfLength) ? The buffer part is better, I am going to try to memorise it. At this point the 10 different ways of having to use file methods are overwhelming, almost want to quit, don't know how I'm going to remember it all. Maybe I'm going a little fast and need to slow down and spend some time on this, as well as on wrapper classes, which also sound stupid to me, why the hell would I want to do that, if I could just instantiate existing classes and overwrite their methods. Overly complex again, but I also know that I now think emotionally due to struggling a bit, and need to realise that people with years of experience probably has a practical use for it, lol! Thanks again for your insights.

Guadalupe Gagnon

Level 37 , Tampa, United States

5 June 2019, 15:22

solution

I had a hard time figuring out all these differen reader/writer classes: Reader/Writer, BufferedReader/Writer; InputStreams and OutputStreams, those last 2 but buffered. Then you have StringReader/Writer, FileReader/Writer, ByteArrayInput/Output.... etc etc etc. They all have their uses but get a little overwhelming at first. What i meant with the duplicate code is you can change lines 29- 45 to this:

if ((fileLength % 2)==0){
   halfLength = (fileLength /2);
else{
   halfLength = (fileLength /2);
   halfLength --;
}

long i = 0;
while (inStream.available()>0){
   for (i = 0;i< halfLength;i++){
      int n = inStream.read();
      outStream1.write(n);
   }
   while (inStream.available()>0){
      int n = inStream.read();
      outStream2.write(n);
   }
}

And then remove the lines 46-60. (This is the original code and still has the mathematical error in it). This would accomplish the same exact thing as your original code, but now in 15 less lines +/-. You are correct in your assumption though that the second while loop will pick up reading where the first one left off though.

Henk

Level 19 , Pretoria, South-Africa

6 June 2019, 05:25

thanks :) :)

Darko Jakimovski

Level 18 , Kriva Palanka, Macedonia, The Former Yugoslav Republic of

6 June 2019, 11:06

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      File file1 = new File(br.readLine());
      File file2 = new File(br.readLine());
      File file3 = new File(br.readLine());

      FileInputStream fis1 = new FileInputStream(file1);
      FileOutputStream fos2 = new FileOutputStream(file2);
      FileOutputStream fos3 = new FileOutputStream(file3);
      byte[] fullData = new byte[fis1.available()];
      int count = fis1.read(fullData);

      int modulo = count % 2;
      int halfData;

      if (modulo == 0)
          halfData = count / 2;
      else {
          halfData = count / 2 + modulo;
      }

      fos2.write(fullData, 0, halfData);
      fos3.write(fullData, halfData, count);
      fis1.close();
      fos2.close();
      fos3.close();

How is this not legit? What am I missing?