HKID Check Digit

/** 
 * Calculate the check digit of HKID
 * - Cheung Ho Yin, 20070912
 * */

import java.util.Scanner;

public class ID {

	// Define aliases for ASCII character code
	private static final int ASC_0=48, ASC_A=65;

	// Return the checkDigit produced from hkid
	private static char checkDigit( String hkid ){
		
		// Step 1: Map the leading alphabet to number: A=1, B=2, ... Z=26
		// e.g. A is 65 in ASCII, so 65-65+1 gives 1
		int s=((int)hkid.charAt(0)-ASC_A+1)*8;

		// Step 2: Add the other digits like A*8 + 1*7 + 2*6 + ... + 6*2
		for(int i=1; i<7; i++){ s += ((int)hkid.charAt(i)-ASC_0) * (8-i); }

		// Step 3: s = 11 - (s mod 11)
		s = 11-s%11; // s can be 1, 2, 3, ..., 10, 11.

		// Step 4: If s is 10, return A. If s is 11, return 0. Otherwise return s.
		s = s%11; return (s==10)?'A':(char)(s+ASC_0);
	}

	// Main method begins execution of Java application
	public static void main( String [] args )
	{
		System.out.print( "Enter the first 7 digits of your HKID (e.g. A123456): " );
		Scanner input = new Scanner( System.in );
		String hkid = input.nextLine(); // read in a whole line, assuming correct format
		System.out.printf( "Your ID number is %s(%c).\n", hkid, checkDigit(hkid));
	} //end method main

} // end class ID