вроде как то я не то делаю вроде.... может задание не понял ?
package com.javarush.task.task18.task1825;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;
/*
Собираем файл
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileOutputStream outputStream = new FileOutputStream("c:/arc/444.txt", true);
TreeSet <String> set = new TreeSet<>();
String fileName;
while (true) {
fileName = reader.readLine();
if (fileName.equals("end")) { break; }
set.add(fileName); }
FileInputStream inputStream = null;
for (String a : set) {
inputStream = new FileInputStream(a);
byte [] buffers = new byte[10000];
if (inputStream.available() > 0)
{
int data = inputStream.read(buffers);
outputStream.write(buffers, 0, data);
}}
reader.close();
inputStream.close();
outputStream.close();
}
}