Question

i am looking at the code of a project called MyTracks:

http://code.google.com/r/jrgert-polar-bluetooth/source/browse/MyTracks/src/com/google/android/apps/mytracks/services/sensors/PolarMessageParser.java?r=ebc01faf49550bc9801633ff38bb3b8ddd6f5698

Now I am having problems with the method isValid(byte[] buffer). I don´t understand what exactly is he checking here. We want to know if the first byte in the array is the header containing 0xFE. I don´t quite understand the following lines :

 boolean goodHdr = ((buffer[0] & 0xFF) == 0xFE);
 boolean goodChk = ((buffer[2] & 0xFF) == (0xFF - (buffer[1] & 0xFF)));
 return goodHdr && goodChk;    

any ideas?

Answer 1

&0xff simply converts signed byte to unsigned int for doing the comparison