ignore

ignore this.......Rob was right

The Serial.read() method is not the only (or, in your case, best) method to read the serial data. The Arduino should be sending data to the serial port using Serial.println(someData);. Then, the Processing application can use the Serial.readUntil() method (look it up!) to read the data up to the carriage return or line feed AS A STRING.

You are currently only reading the 1st character of the data sent, as an integer.

Note that RFID numbers (strings) can be much larger than a int or even a long can hold.
If you need to compress it consider BCD (array) representation, the conversion from string to BCD array and back is straightforward. Compression factor will be ~2 (depending on #digits)

Looked at the last Arduino code from the other thread (difficult if info is over multiple threads),
You have an array of 10 chars to collect the RFID code in. But you forgot that a char array allways need an char(0) or \0 at the end. That should be fixed. So chance the size of the array to 11 and add the ‘\0’ to the end by adding - code[10] = ‘\0’;

As the array is not closed properly the Serial.println(code) can print more than code alone as it prints until it find a \0 in memory…

Another option could be printing characterwise iso per string:
for (int i=0; i< 10; i++) Serial.print(code*);*
Then you could even send the char’s as fast as they come in from the RFID and you do not need to collect them. Drawback is that this is more error prone.