I have tested with the value from excercise description, and in my opinion it works
package pl.codegym.task.task19.task1908;
/*
Wybieranie numerów
*/
import java.io.*;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
String s1 = bufferedReader.readLine();
String s2 = bufferedReader.readLine();
FileReader fileReader = new FileReader(s1);
FileWriter fileWriter = new FileWriter(s2);
BufferedReader bufferedReader1 = new BufferedReader(fileReader);
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
while (fileReader.ready()){
int i = fileReader.read();
boolean isAnumber = false;
String filecontent = "";
while (fileReader.ready()){
filecontent = bufferedReader1.readLine();
String[] s = filecontent.split(" ");
for (int j = 0; j < s.length; j++) {
try{
Integer.parseInt(s[j]);
if(isAnumber==true){
bufferedWriter.write(" "+s[j]);
} else {
bufferedWriter.write(s[j]);
isAnumber = true;
}
}catch (NumberFormatException e){
}
}}
} bufferedReader.close();
bufferedReader1.close();
bufferedWriter.close();
fileReader.close();
fileWriter.close();
}
}