то ли я содержимое неправильно добавляю в лист , или я вообщем позабыл принцип действия
package com.javarush.task.task18.task1819;
/*
Объединение файлов
*/
import java.io.*;
import java.util.ArrayList;
public class Solution {
public static void main(String[] args)throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String filename1=reader.readLine();
String filename2=reader.readLine();
ArrayList<Integer>list =new ArrayList<>();
FileInputStream fileInputStream2 = new FileInputStream(filename2);
FileInputStream fileInputStream1 = new FileInputStream(filename1);
FileOutputStream fileOutputStream = new FileOutputStream(filename1);
byte[] bytes = new byte[1024];
while (fileInputStream2.available()>0){
list.add(fileInputStream2.read(bytes));
} while (fileInputStream1.available()>0){
list.add(fileInputStream1.read(bytes));
}
for (Integer s : list){
fileOutputStream.write(s);
}
fileOutputStream.close();
fileInputStream2.close();
fileInputStream1.close();
reader.close();
}
}