Java Programming

I have to make nmea checksum method, that will create checksum for selected string:

the checksum value is derived by the same method of NMEA standard. its calculated by XOR the 8 bits of each character before in the sentence excluding .
The HEX value of the most significant and least significant 4 bits of the result are converted to 2 ASCII characters.

My method:

String c; 
        int checksum=0;        

	        	 for (int i = 0; i < command.length(); i++) {
	        			// if it is first value for the checksum
	    				if (i == 0)
	    				{	    			    				  					
	    					checksum = (byte)command.charAt(i);	

	    				}
	    				else
	    				{
	    					checksum = checksum ^ (byte)command.charAt(i);

	    				}

	        	 }
           

If i enter: GSC,011412000010789,M2(P3=500)

i get:

checksum: 114
Integer.toHexString(checksum): 72

I get the same result in:

+[
|http://nmeachecksum.eqth.net/]*But in the manual is the result:* +*35*

What do i have to do to get this result? I think it is someting about 4 most al least important bits? How to get them?