Project-Error-Correcting-Encoder-Decoder

This is my implementation of Jet Brains Error-Correcting-Encoder-Decoder project stage 5/5. Errors are inevitable both in life and in the digital world. Errors occur here and there and everywhere, and this project helped me to not only imitate this process, but also learn how to cope with errors. Emulating random errors on the bit-level, manipulating the bits and using the algorithm, and finally making it possible to decode the message that contains an error in a memory-efficient and complex way.

This is how program works. Input (encode, send or decode) was randomly generated by Intellij Idea Edu system in order to test the program output:

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My code:

import javax.xml.transform.sax.SAXSource;

import java.io.*;

import java.util.Arrays;

import java.util.Random;

import java.util.Scanner;

import java.util.StringTokenizer;

public class Main {

public static void main(String[] args) throws IOException {
    Scanner scan = new Scanner(System.in);
    switch (scan.nextLine()) {

        case "encode":
            encodeIt("send.txt", "encoded.txt");
            break;

        case "send":
            sendIt("encoded.txt", "received.txt");
            break;

        case "decode":
            decodeIt("received.txt", "decoded.txt");
            break;
        default:
            break;
    }
    scan.close();
}

static void encodeIt(String inFile, String outFile) throws IOException {
    try (FileInputStream inputStream = new FileInputStream(inFile);
         FileOutputStream fileOutputStream = new FileOutputStream(outFile, false);) {
        byte[] originalBytes = inputStream.readAllBytes();
        StringBuilder sb = new StringBuilder();

        for (byte b : originalBytes) {
            sb.append(String.format("%08d", Integer.parseInt(Integer.toBinaryString(b))));
        }
        for (int i = 0; i < sb.length(); i += 4) {
            StringBuilder sb1 = new StringBuilder();
            String auxA = sb.substring(i, i + 4);
            System.out.print(auxA + " ");

            String[] auxB = {"x", "x", String.valueOf(auxA.charAt(0)), "x", String.valueOf(auxA.charAt(1)),
                    String.valueOf(auxA.charAt(2)), String.valueOf(auxA.charAt(3)), "0"};

            auxB[0] = String.valueOf((Integer.parseInt(auxB[2]) + Integer.parseInt(auxB[4]) + Integer.parseInt(auxB[6])) % 2);
            auxB[1] = String.valueOf((Integer.parseInt(auxB[2]) + Integer.parseInt(auxB[5]) + Integer.parseInt(auxB[6])) % 2);
            auxB[3] = String.valueOf((Integer.parseInt(auxB[4]) + Integer.parseInt(auxB[5]) + Integer.parseInt(auxB[6])) % 2);

            for (String s : auxB) {
                sb1.append(s);
            }

            String aux4 = String.valueOf(sb1);
            System.out.print((byte) Integer.parseInt(aux4, 2) + " ");
            fileOutputStream.write((byte) Integer.parseInt(aux4, 2));
            System.out.println();

        }
    }
}

static void sendIt(String inFile, String outFile) throws IOException {
    try (FileInputStream inputStream = new FileInputStream(inFile);
         FileOutputStream fileOutputStream = new FileOutputStream(outFile, false);) {

        byte[] byteS = inputStream.readAllBytes();
        for (byte b : byteS) {
            Random random = new Random();
            b ^= 1 << random.nextInt(8);
            fileOutputStream.write(b);
        }

    }

}

static void decodeIt(String inFile, String outFile) throws IOException {
    try (FileInputStream inputStream = new FileInputStream(inFile);
         FileOutputStream fileOutputStream = new FileOutputStream(outFile, false);) {
        byte[] byteS = inputStream.readAllBytes();
        StringBuilder sb = new StringBuilder();
        StringBuilder sb3 = new StringBuilder();
        for (byte b : byteS) {
            String aux = "";
            if (b >= 0) {
                aux = String.format("%08d", Integer.parseInt(Integer.toBinaryString(b)));
            } else {
                aux = Integer.toBinaryString(b).substring(24);
            }
            sb.append(aux);
        }

        for (int i = 0; i < sb.length(); i += 8) {
            StringBuilder sb1 = new StringBuilder();
            String[] aux = sb.substring(i, i + 7).split("");
            int pos = 0;
            if (Integer.parseInt(aux[0]) != (Integer.parseInt(aux[2]) +
                    Integer.parseInt(aux[4]) + Integer.parseInt(aux[6])) % 2) {
                pos += 1;
            }

            if (Integer.parseInt(aux[1]) != (Integer.parseInt(aux[2]) +
                    Integer.parseInt(aux[5]) + Integer.parseInt(aux[6])) % 2) {
                pos += 2;
            }

            if (Integer.parseInt(aux[3]) != (Integer.parseInt(aux[4]) +
                    Integer.parseInt(aux[5]) + Integer.parseInt(aux[6])) % 2) {
                pos += 4;
            }

            if (pos > 1) {
                if (Integer.parseInt(aux[pos - 1]) == 0) {
                    aux[pos - 1] = "1";
                } else {
                    aux[pos - 1] = "0";
                }
            }
            for (String s : aux) {
                sb1.append(s);
            }

            sb3.append(sb1.charAt(2));
            sb3.append(sb1.charAt(4));
            sb3.append(sb1.charAt(5));
            sb3.append(sb1.charAt(6));
        }
        for (int i = 0; i < sb3.length(); i += 8) {
            fileOutputStream.write((char) Integer.parseInt(sb3.substring(i, i + 8), 2));
        }

    }

}

}