Trouble decoding the data from the random file

Question

I have to make a program that reads input from a file, encodes it with random characters and integers into a random file and then decode the randomfile to print the original data from the input file in the console.

I did this for the encoding part:

public class Encoder implements IEncoder {

    public void encode(String inputFileName, String outputFilePath) throws IOException{
        File file = new File(inputFileName);

        //load characters into the character array 
        char[] chars = {'a', 'b', 'c', 'd','e', 'f', 'g', 'h', 'i', 'j', 'k', 'l'};

        RandomAccessFile randFile = new RandomAccessFile(outputFilePath, "rw");

        ArrayList<Character> list = new ArrayList<Character>();

        String k = "";

        //scan  input file, save into string 

        try {
            Scanner scan = new Scanner(file);
            while(scan.hasNextLine()) {
                k=k+scan.nextLine();
            }

        scan.close();
        } catch (FileNotFoundException e) {
            System.out.println("There was an issue with the file...");
        }

        //save data from the input file into the ArrayList 

        for(int i = 0; i < k.length(); i++) {
            list.add(k.charAt(i));
        }

        //write each character into a binary file, along with a random integer n, followed by n random characters

        for(int j = 0; j< list.size()-1; j++) {
            int n = ThreadLocalRandom.current().nextInt(1, 20 + 1);
            randFile.writeChar(list.get(j));
            randFile.writeInt(n);

            for (int m = 0; m < n; m++) {
                int z = ThreadLocalRandom.current().nextInt(1, 11 + 1);
                randFile.writeChar(chars[z]);
            }
        }

        randFile.writeChar(list.get(list.size() - 1));
        randFile.writeInt(-1);
        randFile.close();
    }
}

This is for the decoder.

public class Decoder implements IDecoder {

    @Override
    public void decode(String filePath) throws IOException {

        //read the random access file 
        RandomAccessFile randFile = new RandomAccessFile(filePath, "r");

        //create a string to print the output to console
        String k ="";

        //initialize the array list 
        ArrayList<Character> list = new ArrayList<Character>();



        for(int i = list.size()-1 ; i> 0 ; i--) {
            char c = randFile.readChar();
            int n = randFile.readInt();
            // int z = ThreadLocalRandom.current().nextInt(1, 20 + 1);

            for(int m = 0; m < n; m++) {
                // int x = ThreadLocalRandom.current().nextInt(1, 11 + 1);
                k = k + c;
            }
        }

        //print the output and close the random access file 
        System.out.println("The data is" + k);
        randFile.close();
    }

}

My main issue is that I can't figure out a way to store the characters from the randomfile skipping all those random stuff.

this is the question:

You are to write a Java program to encode and decode a text file. The encoder reads a message stored in a plain text file, encodes it, and stores it in a binary file. The decoder reads the binary file, decodes the message and prints it to the console.

The encoding algorithm works as follows:
• Each character c in the message is followed by a randomly-generated number n ranging from 1 to 20. n is the number of bytes of random data between c and the next character in the message. So, after writing c followed by n to the file, there should be n byte locations (with random data) before the next character c is written.
• The last character is followed by the number -1 which indicates the end of the message.
• Each character stored in the binary file occupies 2 bytes while each integer occupies 4 bytes. Random data is stored between the integer following each character and the next character.

Answer 1

My main issue is that I can't figure out a way to store the characters from the randomfile skipping all those random stuff.

The builder you are looking for is a StringBUilder .

Additionally you should look at the skipBytes method of your reader.

Putting those together, your decoder would look something like this (not accounting for edge cases):

   public class Decoder implements IDecoder {

    @Override
    public void decode(String filePath) throws IOException {

        //read the random access file 
        RandomAccessFile randFile = new RandomAccessFile(filePath, "r");

        //create a string to print the output to console
        StringBuilder builder = new StringBuilder();

        while(true) {
            char c = randFile.readChar();
            builder.append(c);
            int n = randFile.readInt();
            if(n == -1) break;
            randFile.skipBytes(n);

        }

        //print the output and close the random access file 
        System.out.println("The data is" + builder.toString());
        randFile.close();
    }

}