HEX

public class Hex
{
    private static final char digits[] =
            {
                '0', '1', '2', '3', '4', '5', '6', '7',
                '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
            };

    public static class Decoder
    {
        private int filled = 0;
        private byte data[];
        private int work[] = {0, 0};

        public Decoder()
        {
            data = new byte[256];
        }

        public void decode(String encoded)
        {

            int estimate = 1 + encoded.length() / 2;

            if (filled + estimate > data.length)
            {
                int length = data.length * 2;
                while (length < filled + estimate)
                {
                    length *= 2;
                }
                byte[] newdata = new byte[length];

                System.arraycopy(data, 0, newdata, 0, filled);
                data = newdata;
            }

            for (int i = 0; i < encoded.length(); ++i)
            {
                work[0] = Character.digit(encoded.charAt(i), 16);
                i++;
                work[1] = Character.digit(encoded.charAt(i), 16);
                data[filled++] = (byte) (((work[0] << 4) | (work[1])) & 0xff);
            }
        }

        public byte[] drain()
        {
            byte[] r = new byte[filled];
            System.arraycopy(data, 0, r, 0, filled);
            filled = 0;
            return r;
        }

        public byte[] flush() throws IllegalStateException
        {
            return drain();
        }

        public void reset()
        {
            filled = 0;
        }

    }

    public static class Encoder
    {
        private StringBuffer output;

        public Encoder(int size)
        {
            output = new StringBuffer(size * 2);
        }

        private void encodeBlock(byte work)
        {
            output.append(digits[(work & 0xF0) >>> 4]);
            output.append(digits[(work & 0x0F)]);
        }

        public void encode(byte[] data)
        {
            encode(data, 0, data.length);
        }

        public void encode(byte[] data, int offset, int length)
        {
            int plainIndex = offset;

            while (plainIndex < (offset + length))
            {
                encodeBlock(data[plainIndex]);
                plainIndex++;
            }
        }

        public String drain()
        {
            String r = output.toString();
            output.setLength(0);
            return r;
        }

        public String flush()
        {
            return drain();
        }
    }

    public static void main(String[] args)
    {
        boolean printData = false;
        int randomLimit = 500;

        for (int myCount = 0; myCount < 10000; myCount++)
        {
        byte raw [] = new byte[(int)(Math.random() * randomLimit)];

        for (int i = 0; i < raw.length; ++i)
        {
            if ((i % 1024) < 256)
                raw[i] = (byte)(i % 1024);
            else
                raw[i] = (byte)((int)(Math.random() * 255) - 128);
        }
        Hex.Encoder encoder = new Hex.Encoder(100);
        encoder.encode(raw);

        String encoded = encoder.drain();

        Hex.Decoder decoder = new Hex.Decoder();
        decoder.decode(encoded);
        byte check[] = decoder.flush();

        String mesg = "Success!";
        if (check.length != raw.length)
        {
            mesg = "***** length mismatch!";
        }
        else
        {
            for (int i = 0; i < check.length; ++i)
            {
                if (check[i] != raw[i])
                {
                    mesg = "***** data mismatch!";
                    break;
                }
            }
        }
        if (mesg.indexOf("Success") == -1)
        {
            System.out.println(mesg + myCount);
            break;
        }

        if (printData)
        {
            System.out.println("Decoded: " + new String(raw));
            System.out.println("Encoded: " + encoded);
            System.out.println("Decoded: " + new String(check));
        }
        }
    }
}