HKID validation in Java

Courtesy to http://keatonchan.blogspot.hk/2009/08/hkid-check-digit-calculation-algorithm.html for algorithm. Revised edition:

public class HKID { 
 public static boolean validate(String prefix, String serial, String checkdigit) { 
   String prefixU = prefix.toUpperCase();
   long value = 0; if (prefixU.length() == 2) { 
     value += (prefixU.charAt(0) - 55) * 9 + (prefixU.charAt(1) - 55) * 8; 
  } else if (prefixU.length() == 1) { 
     value += 36 * 9 + (prefixU.charAt(0) - 55) * 8; 
   } 
   for (int i = 0; i < 6; i++) { 
     value += Integer.parseInt(serial.substring(i, i + 1)) * (7 - i); 
   } 
   long reminder = value % 11; 
   long valid_checkdigit = 11 - reminder;
   if ("A".equalsIgnoreCase(checkdigit) && valid_checkdigit == 10) { 
      return true; 
   } 
   try { 
     if (valid_checkdigit == Integer.parseInt(checkdigit)) { 
       return true; 
     } 
   } catch (Exception e) { } 
   return false; 
 }  
}

PS> Objective-C version

#import "HKID.h"

@implementation HKID

+ (BOOL) validateWithPrefix:(NSString*) prefix serial:(NSString *) serial checkdigit:(NSString*) checkdigit {

    NSString* prefixU = [prefix uppercaseString];

    int value = 0;

    if ([prefixU length] == 2) {

        value += (([prefixU characterAtIndex:0] - 55) * 9) + (([prefixU characterAtIndex:1] - 55) * 8);

    } else if ([prefixU length] == 1) {

        value += 36 * 9 + ([prefixU characterAtIndex:0] - 55) * 8;

    } else {

        return false;

    }

    if ([serial length] != 6) return false;

    if ([checkdigit length] != 1) return false;

    for (int i = 0; i < 6; i++) {

        int tempValue = [[serial substringWithRange:NSMakeRange(i,1)] intValue];        

        value += tempValue * (7 - i);

    }

    long reminder = value % 11;

    long valid_checkdigit = 11 - reminder;

    NSCharacterSet *digitSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];

    if ([[checkdigit stringByTrimmingCharactersInSet:digitSet] isEqualToString:@""]){ // all digits

        if ([checkdigit intValue] == valid_checkdigit) {

            return true;

        }

    } else if ([@"A" isEqualToString:checkdigit]) {

        if (valid_checkdigit == 10) {

            return true;

        } else {

            return false;

        }

    }

    return false;

}

@end