Question

I have a message

static int[] message = {
        0x01, 0x10, 0x00,
        0x01, // port addres 01 - 08
        0x00, 0x01, 0x02,
        0x06, 0x00,
        0xA4, 0x21
};

I know the data are right, as of I’m writing them to COM port with RXTX, and I got right HW reaction

I know that 0x01 is 1 value, and sent really like 01 (which is two bits, quarter byte long)

When I need to adjust the message, is generating values like this right?

message[index] = 1 & 0xff

I see the output of this snippet, and it looks properly

for (int i = 0; i < 255; i++) {
    System.out.println(i & 0xff);
}

Is there any sheet you’d recommend me to read?
Is storing these numbers in int right, as we cannot use byte (-128, +127) for values up to <0x00, 0xFF> range

Answer 1

You probably want to use a ByteBuffer for what you need, and wrap it under a class.

I don’t know your exact message format, but let’s say for a moment this is 3 bytes of data and 1 byte of a port:

public final class Message
{
    private static final MESSAGE_SIZE = 4;
    private static final PORT_OFFSET=3;

    private final ByteBuffer buf;

    public Message()
    {
        buf = ByteBuffer.allocate(MESSAGE_SIZE);
    }

    public void setPort(final byte b)
    {
        buf.put(PORT_OFFSET, b);
    }

    // etc

    public byte[] getRaw()
    {
        return buf.array();
    }
}

You can even use ByteBuffer’s hashCode() and equals() to compare messages, if you only ever use absolute get/put methods (otherwise quite a bit of gymnastic is in order).

I used this technique to read/write NRPE packets.