Chapter 17 Exercise 15, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

17.15  (Decrypt files)
Suppose a file is encrypted using the scheme in Programming Exercise 17.14.
Write a program to decode an encrypted file. Your program should prompt the
user to enter an input file name for the encrypted file and an output file
name for the unencrypted version of the input file.

import java.io.*;

public class Exercise_15 {

    public static void main(String[] args) {

        if (args.length != 2) {
            System.out.println("Invalid number of arguments. Usage: src target");
        }

        try (BufferedInputStream in = new BufferedInputStream(new FileInputStream(args[0]));
             BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(args[1]))) {

            int buffer;
            while ((buffer = in.read()) != -1) {
                out.write(buffer - 5);
            }

            System.out.println("File Unencrypted!");
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}