What is wrong?

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I tried doing a list, array, string and reverse all - nothing works. Can You tell me where is mistake because this task seems easy. I think i miss something important.

package pl.codegym.task.task18.task1809; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.Collections; import java.util.*; 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(); ArrayList<Byte> list = new ArrayList<Byte>(); FileInputStream inputStream = new FileInputStream(file1); FileOutputStream outputStream = new FileOutputStream(file2); byte[] buffer = new byte[10000]; while (inputStream.available() > 0){ int count = inputStream.read(buffer); } Collections.reverse(Arrays.asList(buffer)); for(int i = 0; i < buffer.length; i++){ outputStream.write(buffer[i]); } reader.close(); inputStream.close(); outputStream.close(); } }

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Guadalupe Gagnon

Poziom 37 , Tampa, United States

11 grudnia 2023, 19:28

#1 When an Array of primitives is initialized each index will be assigned the value 0 (which is 0 for numbers or false for boolean), which for this task would be junk data. Your buffer length is hard coded to 10000. This will only work if the file has exactly 10,000 bytes to read. If it is less than 10,000 then your array will only be filled with data up to the amount of bytes in the file and then junk data. Take, for example, if you had a buffer of length 5 and there were only 3 bytes to read in the file of simply 1, 2, and 3. The values in the buffer, after reading the file will be {1, 2, 3, 0, 0}, and if you reverse that you get {0, 0, 3, 2, 1}, and file2 will have those values in it, which would be incorrect. In the case where the buffer is too small for the amount of bytes then bytes will be over written, and lost, in the buffer. Take, for example, if you have a buffer of length 5 and there are 7 bytes in the file that are simply 1 through 7. The buffer would hold the first 5 bytes on line 26 so that the buffer would be {1,2,3,4,5}. There would be 2 bytes left after that read and the loop would continue to a new cycle. The 2 bytes left would over write the first two bytes of the buffer so the buffer would then be {6, 7, 3, 4, 5}. If you reversed that and put it in file2 this would not be correct becase bytes 1 and 2 are missing. #2 Arrays.asList() doesn't work for primitive types. You can read more on stackoverflow here 'primitives and .asList()' The task doesn't say that you need to reverse the bytes in the array; only that the bytes need to be written to file2 in reverse. Java doesn't provide utility to reverse a primitive array so if you still want to reverse it before writing then you will need to write code that does it yourself.

robert1a2b

Poziom 22 , Poland, Poland

12 grudnia 2023, 10:03

Thanks. I used for loop, but still doesn't work. public static void main(String[] args) throws IOException{ BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String file1 = reader.readLine(); String file2 = reader.readLine(); ArrayList<Byte> list = new ArrayList<Byte>(); FileInputStream inputStream = new FileInputStream(file1); FileOutputStream outputStream = new FileOutputStream(file2); byte[] buffer = new byte[inputStream.available()]; while (inputStream.available() > 0){ int count = inputStream.read(buffer); for(int i = inputStream.available(); i > 0; i--){ outputStream.write(buffer, 0, count); } } reader.close(); inputStream.close(); outputStream.close(); }