🚀 go-pugleaf

Try using Integer.parseInt(String s, int radix)
where the radix in this case needs to be 16.

OTOH, you could decompose the integer into bytes
and recompose it using shift-and-mask. I haven't 
tried the following, but you should get the idea...

byte[] sumbytes = new byte[4];
byte[3] = (byte) checksum & 255;
byte[2] = (byte) (checksum >> 8) & 255;
byte[1] = (byte) (checksum >> 16) & 255;
byte[0] = (byte) (checksum >> 24) & 255;

rebuild it...
int checksumReceived = rxpacket[checksumposition];
checksumReceived <<= 8;
checksumReceived += ((int) rxpacket[checksumposition + 2]) & 255;
checksumReceived <<= 8;
checksumReceived += ((int) rxpacket[checksumposition + 3]) & 255;
checksumReceived <<= 8;
checksumReceived += ((int) rxpacket[checksumposition + 4]) & 255;

Steve