Что не так написал?
package com.javarush.task.task19.task1908;
/*
Выделяем числа
*/
import java.io.*;
import java.util.ArrayList;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader1 = new BufferedReader(new InputStreamReader(System.in));
String file1 = reader1.readLine();
String file2 = reader1.readLine();
reader1.close();
FileReader reader = new FileReader(file1);
FileWriter writer = new FileWriter(file2);
String s = "";
while (reader.ready()) {
s += (char) reader.read();
}
reader.close();
String[] number = s.split(" ");
ArrayList<Integer> numbers = new ArrayList<>();
for (int i = 0; i < number.length; i++) {
try {
numbers.add(Integer.parseInt(number[i]));
}
catch (Exception e) {
e.printStackTrace();
}
}
for (int num : numbers) {
writer.write(num);
}
writer.close();
}
}