CodeGym/Help with Java Tasks/Please i need some help. I tried it over and over again u...

Level 22

Potsdam

19.02.2019
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Please i need some help. I tried it over and over again unfortunately i could not figure out.

Question about the task

Splitting a file

Java Core, Level 8, Lesson 5

Resolved

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) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String file1 = reader.readLine(); String file2 = reader.readLine(); String file3 = reader.readLine(); //Create a FileInputStream object bound to file1 FileInputStream inputStream = new FileInputStream(file1); //Create a FileOutputStream object to write byte to a file2 FileOutputStream outputStream2 = new FileOutputStream(file2); FileOutputStream outputStream3 = new FileOutputStream(file3); int count = 0; while (inputStream.available() > 0) { byte[] buffer = new byte[inputStream.available()]; count = inputStream.read(buffer); if (count % 2 != 0) { buffer = new byte[count]; int data = inputStream.read(buffer,0, count); outputStream2.write(buffer, 0, data); } else { count = (count / 2) ; buffer = new byte[count]; int data = inputStream.read(buffer); outputStream3.write(buffer, 0, data); } } inputStream.close(); outputStream2.close(); outputStream3.close(); } }

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Sela

Level 20 , Poland

22 September 2020, 06:52

if you use buffer size of file length there is no need to use while loop to read from the file, but this is a solution only for small files (which contradicts with the idea of buffering). the calculation of the size of target files is overwhelming here. better use the simple version like this:

int noOfBytes = inputStream.available();//total no of bytes
int secondHalf = noOfBytes / 2;//the smaller half - casting to int removes the floating point
int firstHalf = noOfBytes - secondHalf;//the rest is bigger or equal to first

you don't even need to use modulus operator.

Nouser

Level 36 , Germany

22 September 2020, 08:29

excellent solution, I like yours a lot more than mine (with modulo)

firstHalf = secondHalf = fileLength / 2;
if (fileLength % 2 != 0) firstHalf++;

Andrew

Level 29 , Seattle, United States

19 February 2019, 18:11

I'll try to explain this coherently but the thing that made everything make sense for me was understanding how the write(byte[] b, int off, int len) works. Let's say: int file1size = inputStream.available(); // file1size = 10 byte[] buffer = new byte[file1size]; // new byte[10] inputStream.read(buffer); // read all contents of file1 to our byte[] called buffer Let's write a portion of the buffer contents to our output file2. outputStream.write(buffer, 0, file1size / 2); // file1size / 2 = 10 / 2 = 5 Now let's break down exactly what is happening here: - outputStream.write indicates that we want to write bytes to a specific location - buffer is what content to write (the byte array called buffer has 10 bytes in it, index 0 - 9) - 0 is what index in the byte[] to start at (0 = start writing from buffer[0]) - file1size / 2 is how many indexes to write, not what index # to end at (if this number is 5, then it means write the next 5 bytes from the byte[] into the file, beginning at your indicated starting index). If this number was 2 then it would write buffer[0] and buffer[1] to the file. So if you write something like outputStream.write(buffer, 4, file1size), it will start at buffer[4] and try to write until buffer[14], because file1size is 10, an index that is out of bounds.

y-meyer2

Level 28 , Germany, Germany

31 January 2022, 20:12

Thanks a lot. I thought the len is until which index of the array.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 14:29

erase line 24-41 and just replace with:

byte[] buffer = new byte[inputStream.available()];
while (inputStream.available() > 0) {
   inputStream.read(buffer);
}

Your code is good up until then. Now you need to figure out how to write half of what buffer holds to file2 and the other half to file3

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 16:20

Could you please help me figuring out. I could not figure it out. while (inputStream.available() > 0) { int data = inputStream.read(buffer); System.out.println(data); if (data % 2 != 0) { int half1 = (data / 2) + (data %2); outputStream1.write(buffer, 0, half1); } else { outputStream2.write(buffer, 0, data/2); } } I am really having hard time with this

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 16:26

the way that I solved it was that I converted the buffer to an ArrayList<integer>, then created a second ArrayList<Integer> to hold half the values. It was easy to split them with a while loop:

while (firstHalfArrayList.size() < bufferArrayList.size()){
   //this will stop when the two arraylists are the same size, or the first is 1 larger
   firstHalfArrayList.add(bufferArrayList.get(0));
   bufferArrayList.remove(0);
}

This will give you a first and second half of the original file, write the firstHalfArrayList to file2 and the bufferArrayList to file3

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 16:46

could this not be solved without using a List? Actually i got the first half right without using any List. The problem is now getting the second half. while (inputStream.available() > 0) { int data = inputStream.read(buffer); int half1 = (data / 2) + (data % 2); outputStream1.write(buffer, 0, half1); int half2 = data/2; // hier is where i am strugling with outputStream2.write(buffer, 0, half2); }

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 16:48

If not i will use a List. Solving this with list did not come in my mind at all. Thanks

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 17:16

of course it can be solved without a list. It could be solved without using a buffer

int size = inputStream.available() / 2 + (inputStream.available() % 2 == 0 ? 0 : 1);
while(inputStream.available() >= size)
    outputStream1.write(inputStream.read());
while((inputStream.available() > 0)
    outputStream2.write(inputStream.read());

(i didn't test this code, just a quick demo. If you use it, test it and make sure that it works.) The ArrayList method made the most sense to me personally when I solved it, but I understand other people see things different and a solve is a solve no matter what.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 17:23

Also, something I just realized: If you read into a buffer you don't need a while loop:

byte[] buffer = new byte[inputStream.available()];
inputStream.read(buffer);

works and you don't needlessly create a loop.

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 17:25

i will try it. this one really gave me some headaches Thanks

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 17:28

But nevertheless using a while loop or not, we have to figure the first half and the second. I am still not getting it very well.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 17:36

Try this:

byte[] buffer = new byte[inputStream.available()];
inputStream.read(buffer);

int size = buffer.length / 2 + (inputStream.available() % 2 == 0 ? 0 : 1) ;
byte[] first = Arrays.copyOfRange(buffer,0,size);
byte[] second = Arrays.copyOfRange(buffer, size, buffer.length);

This should split the buffer into the first half and second half. Then you just need to write them to file.

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 17:52

It looks logical and i will try it later and let you know. I have to work out my way of solving problem. Thanks I will not use the ternäre operator in this way

Guadalupe Gagnon

Level 37 , Tampa, United States

19 February 2019, 17:55

useful

Ok here is what I have come up with using your code, replacing everything from line 14 to 44:

byte[] buffer = new byte[inputStream.available()];
inputStream.read(buffer);

int size = buffer.length/2 + (inputStream.available() % 2 == 0 ? 1 : 0);
outputStream2.write(buffer, 0, size);
outputStream3.write(buffer, size, buffer.length-size);

inputStream.close();
outputStream2.close();
outputStream3.close();

I googled the wikipedia for the country spain, copied and pasted the entire article into a text document to use as 'file1', then added code to time my original solve and code to time your method. My solve took that text document and split it into two in 14439 ms (14.5 second). Your method did the same exact in 10ms........ That is 1440 times faster than mine. Good solve!

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 17:56

Whaou, It good to know.

Angeget

Level 22 , Potsdam, Germany

19 February 2019, 18:26

Hier is my final result byte[] buffer = new byte[inputStream.available()]; int half; while (inputStream.available() > 0) { int data = inputStream.read(buffer); if (data % 2 != 0) half = (data / 2) + (data % 2); else half = data / 2; outputStream1.write(buffer, 0, half); outputStream2.write(buffer, half, data - half); //At this point i have had trouble to understand }

Lex Medeiros

Level 18 , San Jose, Costa Rica

12 September 2019, 13:46

I am trying to split the buffer array into two like this: byte[] buffer = new byte[inputStream.available()]; //Split the Array into two parts and get them ready to be copied into outputstream byte[] firstHalf = Arrays.copyOfRange(buffer, 0, buffer.length/2); byte [] secondHalf = Arrays.copyOfRange(buffer, buffer.length/2, buffer.length); // write the first half of its bytes to file1. FileOutputStream outputStream = new FileOutputStream(file2); outputStream.write(firstHalf,0,firstHalf.length); outputStream.close(); //write second half into file3 . FileOutputStream outputStream1 = new FileOutputStream(file3); outputStream1.write(secondHalf, 0, secondHalf.length); outputStream1.close(); But the program is not validating it. Any insights?

Yiheng Niu

Level 26 , Beijing, China

22 February 2020, 17:04

Just one thing about the comment in Angeget's last reply:

outputStream2.write(buffer, half, data - half);  //At this point i have had trouble to understand

Remember here "data - half" means the length it writes from "half", rather the stop index.

catalinene

Level 29 , Greven, Germany

9 March 2020, 17:04

Can you please explain line 6?

Johannes

Level 27 , Centurion, Pretoria, South-Africa

8 April 2020, 11:58

It doesn't make sense that this works ? If the file size is 7, then the first 3 should go to file 1, and the second 4 to file 2. Angeget's solution (that also worked for me, since nothing I tried that MADE SENSE, worked...__) byte[] buffer = new byte[inputStream.available()]; int half; while (inputStream.available() > 0) { int data = inputStream.read(buffer); if (data % 2 != 0) half = (data / 2) + (data % 2); else half = data / 2; outputStream1.write(buffer, 0, half); outputStream2.write(buffer, half, data - half); } Writing to file 1 will result in the bigger piece (4 from 7 characters) will end up in file 1, not file 2 ?

Angus McDonald

Level 5 , Sydney, Australia

Expert

27 May 2020, 17:30

This one really had me frustrated! Looked at it for far too long. Knew it could be easily managed using the write(byte[] b, int off, int len) method but couldn't get it to work. int filesize = input.available(); byte[] buffer = new byte[filesize]; input.read(buffer); int half; if (filesize % 2 == 0) half = filesize / 2; else half = filesize / 2 + 1; output1.write(buffer, 0, half); output2.write(buffer, half, filesize - half); I was using a while-loop getting errors and decided to give it a whirl without. Turns out it works without! I gather this is because the input.read(buffer) actually reads the whole file as the byte[] buffer size has been set to the amount of available data in the file. The output.write(byte[] b, int off, int len) methods also don't need a loop as it seems we're giving direct instruction to write a known amount of data, thus no loop required.

Goran

Level 41 , Belgrade, Serbia

7 June 2020, 17:12

Replay to Guadalupe GagnonLevel 37 , Tampa last message: This is really nice and fast solution just one correction needed for me to pass. You need to change line 4 into this :

int size = buffer.length / 2 + (buffer.length % 2 == 0 ? 0 : 1);

Because inputStream.available() is not correct case there is no more bytes to read :)