public class Cyfry {
    public static void main(String[] args)
    {
        String dane = "";
        try
        {
            dane = odczyt();
        }
        catch(Exception e)
        {
            //nie działa
        }

        String wynik = new String();
        int i=0;
        int a = Character.getNumericValue(dane.charAt(i));
        while(a!=-1)
        {
            wynik+=zamiana(a);
            i++;
            a = Character.getNumericValue(dane.charAt(i));
        }

        try
        {
            Zapis(wynik);
        }
        catch(Exception e)
        {
            //nie działa
        }



    }
    public static int zamiana(int x)
    {
        if(x==0)
        {
            return 9;
        }
        else
        {
            return x-1;
        }
    }
    public static String odczyt() throws FileNotFoundException, IOException {

    RandomAccessFile f = new RandomAccessFile("C:/users/Jacek/Desktop/cyfry.txt", "r");
    byte []bytes = new byte[255];
    f.read(bytes);
    String dane = new String(bytes);
    f.close();
    return dane;
    }

    public static void Zapis(String dane) throws FileNotFoundException, IOException
    {
        RandomAccessFile f = new RandomAccessFile("C:/users/Jacek/Desktop/cyfry_wynik.txt", "rw");
        byte []bytes = dane.getBytes();
        f.write(bytes);
        f.close();
    }
}