Any hint!?

So, if i understand right, i need to write() the byte array at once with fileoutputstream, no? Now all i have is just a double, how i will transform the double to int to string and byte? Simple casting is not working: String s = String.valueof(x); Byte[] b = s.getBytes(); :( Tk you!

you can either write byte per byte in a loop or pass a byte array to the write method To get a string from an int you could use the valueOf method or just concat with an empty string

fileOutputStream.write(String.valueOf((int) x).getBytes());
fileOutputStream.write(((int) x + "").getBytes());
// the variant writing single bytes
for (byte byt : String.valueOf((int) x).getBytes())
    fileOutputStream.write(byt);

oh, and of course you have Integer.toString() as well.

Try this:

public class Solution {
    static class Debug {
        static public boolean active() {
            return true;
        }
    }
    public static void main(String[] args) throws IOException {
        File file1;
        File file2;
        if(Debug.active()){
            file1 = new File("1.JavaSyntax/src/Test/o1.txt");
            file2 = new File("1.JavaSyntax/src/Test/o2.txt");
        } else {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            file1 = new File(br.readLine());
            file2 = new File(br.readLine());
            br.close();
        }
        System.out.println(file1.getCanonicalPath());
        FileInputStream fileInputStream = new FileInputStream(file1);
        FileOutputStream fileOutputStream = new FileOutputStream(file2);

        byte[] bytes = new byte[fileInputStream.available()];
        fileInputStream.read(bytes);
        String s = new String(bytes);
        fileInputStream.close();

        String[] strings = s.split(" ");

        for(int i = 0; i < strings.length; i++){
            double d = Double.parseDouble(strings[i]);
            if(Debug.active())
                System.out.print(d + " => ");
            double x = Math.round((d * 100)/100);
            if(Debug.active())
                System.out.println((int)x);

            fileOutputStream.write((int) x);

            if(i < strings.length-1){
                fileOutputStream.write(" ".getBytes());
            }
        }

        fileOutputStream.close();
    }
}

About the level that you are now I came up with this "Debug" mode that I would add into my class and then make logic gates in the code (if statements) where the code would use other values or output things to the screen when the debug mode was set to true. You can see the its set to true on line 4 and then on lines 10, 32, and 35 are logic gates that use it. This allows you to write test code while you are doing the task along, such as output statements to see the results of your algorithms. When you get to the point where you are sure the task passes you can set debug mode to false and turn in the task as it is. Most likely it will fail the first couple of times, but it is just as easy as setting debug mode back to true and start working out the bugs. In the code I shared I demonstrated this with your code (plus fixing a couple issues that Lisa had already mentioned). The task still will not pass because there are bugs in it. When I run this code with test values that codegym gave as an example it outputs: 3.49 => 3 3.5 => 4 3.51 => 4 -3.49 => -3 -3.5 => -3 // this line is incorrect. -3.51 => -4 Also, when I check the file that it output the data to it was a bunch of garbage characters. This is because passing an int to the write() method will have it convert that to a char and output the char value and not the int value. P.S. Lines 11 and 12 point to files on my computer, if you decided to copy this code then change those to files on your computer