Very strange output. Please help.

Question about the task

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I get the output 13, 13, 45 for the input suggested in the exercise. What am I doing wrong? I feel it's from the fileinputstream but I can't put my finger on it. Please advise. This is the current form, I don't know why it isn't updated.

public class Solution {
    public static void main(String[] args) throws IOException {
        //write your code here
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        FileInputStream input = new FileInputStream(reader.readLine());
        ArrayList<Integer> nrs = new ArrayList<>();
        int i = 0;
        while ((i = input.read()) != -1) {
            if (input.read() % 2 == 0)
            nrs.add(input.read());
        }
            Collections.sort(nrs);
            for (Integer f : nrs) System.out.println(f);

        reader.close();
        input.close();
    }
}

1. Read a file name from the console.
2. Read a set of numbers from the file.
3. Display only the even numbers, sorted in ascending order.

Example input:
5 8 -2 11 3 -5 2 10

Example output:
-2 2 8 10

Requirements:

The program must read data from the console.
The program must create a FileInputStream using the line read from the console.
The program should display data on the screen.
The program should display all of the even numbers read from the file, sorted in ascending order.
The program must close the input stream used to read the file (FileInputStream).

package com.codegym.task.task13.task1326; /* Sorting even numbers from a file */ import java.io.*; import java.lang.reflect.Array; import java.util.ArrayList; import java.util.Collections; public class Solution { public static void main(String[] args) throws IOException { //write your code here BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); FileInputStream input = new FileInputStream(reader.readLine()); ArrayList<Integer> nrs = new ArrayList<>(); int i = 0; while ((i = input.read()) != -1) { nrs.add(input.read()); } Collections.sort(nrs); for (int j = 0; j < nrs.size(); j++) { if (nrs.get(j) % 2 == 0) System.out.println(nrs.get(j)); } reader.close(); input.close(); } }

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Nouser

Level 36 , Germany

27 November 2020, 21:07

solution

You read the file byte by byte and each single byte you add to your list.That's however not yet numbers, just parts of it. So if you eg. take your output, the 13 13 45 and an ASCII table you'll see that this means two carriage returns (13 13 and a minus (45). What you would need to do is to read an entire line and then parse this to an Integer. Or you read byte by byte till you come to a carriage return and then cast the read bytes to char, to string and finally to an int.

Andrei

Level 41

30 November 2020, 11:50

I thought about your comment, researched to see how I could convert fileinputstream to int and found no relevant answer. Then I checked the solution and observed they used scanner, but I didn't understand at first why Scanner. So I google Scanner and observed that it can work through primitives such as byte, the type of data fileinputstream takes. And then I made it work. Thanks!

Nouser

Level 36 , Germany

30 November 2020, 12:24

Perfect :) As an alternative you could think of using a BufferedReader like...

TreeSet<Integer> sortedNumbers = new TreeSet<>();
try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(reader.readLine())))
) {
    while (in.ready()) {
        try {
            int number = Integer.parseInt(in.readLine());
            if (number % 2 == 0)
                sortedNumbers.add(number);
        } catch (NumberFormatException nfException) {/*if one number can't be parsed continue with next */}
    }
} catch (IOException ioException) { ioException.printStackTrace(); }

for (int number : sortedNumbers)
    System.out.println(number);

Andrei

Level 41

1 December 2020, 08:45

In line 3 you are taking a FileInputStream turning it into an InputStreamReader turning that into a BufferedReader? Also, you used Treeset because it automatically sorts the numbers in ascending order? At line 10, why wouldn't a number be parsed?

Nouser

Level 36 , Germany

1 December 2020, 09:50

solution

Yes, you could also use a FileReader and give that to a BufferedReader. But I like the other possibility more (cause you could chose the encoding via the InputStreamReader). So the BufferedReader requires a Reader in the Constructor (InputStreamReader) and that one likes to see an InputStream (FileInputStream). TreeSet sorts its entries by their natural order. You'll love it (and the TreeMap) later in the course ;) The given example inputs last number, the 10, is followed by a space. If you copy the entire exmple including that trailing space into a file and test that against your code then it'll throw a NumberFormatException cause of that space. "3", "+3", "3.0" are OK "3 ","r3" are not and will give you the exception

Andrei

Level 41

1 December 2020, 10:10

Ah.. wow, ok! Did not think about the various formats of numbers and what could follow after them. Thank you!