что не так?
package com.javarush.task.task18.task1825;
import java.io.*;
import java.util.Comparator;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;
/*
Собираем файл
*/
public class Solution {
public static void main(String[] args) throws IOException {
Scanner s = new Scanner(System.in);
Set<String> filesName = new TreeSet<>(Comparator.comparingInt(o -> Integer.parseInt(o.substring(o.indexOf("part") + 4))));
String fileWriter = null;
while (true) {
String fileName = s.nextLine();
if (fileName.equals("end")) break;
if (fileWriter == null) fileWriter = fileName.substring(0, fileName.lastIndexOf("."));
filesName.add(fileName);
}
s.close();
BufferedReader reader = null;
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileWriter, true)));
for (String files : filesName) {
reader = new BufferedReader(new InputStreamReader(new FileInputStream(files)));
while (reader.ready()) {
writer.write(reader.readLine());
}
reader.close();
}
writer.close();
}
}