Валидация по пункту "В режиме "-d" программа должна расшифровать [fileName] и записать в [fileOutputName]."

package com.javarush.task.task18.task1826;

/*
Шифровка
*/

import java.io.*;

public class Solution {

    public static void main(String[] args) throws IOException {
        String fileName = args[1];
        String fileOutputName = args[2];
        FileInputStream fileInputStream = new FileInputStream(fileName);
        FileOutputStream fileOutputStream = new FileOutputStream(fileOutputName);
        byte bytes;
        if (args[0].equals("-e")) {
            while (fileInputStream.available() > 0) {
                bytes = (byte) (fileInputStream.read());
                fileOutputStream.write(bytes+1);
                fileOutputStream.flush();
            }
        }
        if (args[0].equals("-d")) {
            while (fileInputStream.available() > 0) {
                bytes = (byte) (fileInputStream.read());
                fileOutputStream.write(bytes-1);
                fileOutputStream.flush();
            }
        }
        fileInputStream.close();
        fileOutputStream.close();
    }
}