Строки добавляются, потоки закрыты.
package com.javarush.task.task18.task1827;
/*
Прайсы
*/
import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.nio.file.Files;
import java.nio.file.Paths;
public class Solution {
public static void main(String[] args) throws Exception {
String fileName = new BufferedReader(new InputStreamReader(System.in)).readLine();
Integer max = Files.lines(Paths.get(fileName))
.mapToInt(s -> Integer.parseInt(s.substring(0, 8).trim()))
.max()
.getAsInt();
FileOutputStream outputStream = new FileOutputStream(fileName, true);
switch (args[0]) {
case "-c":
outputStream.write(String.format("%-8d%-30s%-8s%-4s\n", ++max, args[1], args[2], args[3]).getBytes());
break;
}
outputStream.close();
}
}