org.apache.commons.validator.routines.checkdigit
Class LuhnCheckDigit

java.lang.Object
  org.apache.commons.validator.routines.checkdigit.ModulusCheckDigit
      org.apache.commons.validator.routines.checkdigit.LuhnCheckDigit

All Implemented Interfaces:

java.io.Serializable, CheckDigit

public final class LuhnCheckDigit
extends ModulusCheckDigit
implements java.io.Serializable

Modulus 10 Luhn Check Digit calculation/validation.

Luhn check digits are used, for example, by:

• Credit Card Numbers
• IMEI Numbers - International Mobile Equipment Identity Numbers

Check digit calculation is based on modulus 10 with digits in an odd position (from right to left) being weighted 1 and even position digits being weighted 2 (weighted values greater than 9 have 9 subtracted).

See Wikipedia for more details.

Since:

Validator 1.4

Version:

$Revision: 493905 $ $Date: 2007-01-08 03:11:38 +0100 (Mo, 08. Jan 2007) $

See Also:

Serialized Form

Field Summary

static CheckDigit	INSTANCE Singleton Luhn Check Digit instance
private static int[]	POSITION_WEIGHT weighting given to digits depending on their right position

Constructor Summary

LuhnCheckDigit()
Construct a modulus 10 Luhn Check Digit routine.

Method Summary

protected int

weightedValue(int charValue, int leftPos, int rightPos) Calculates the weighted value of a charcter in the code at a specified position.

Methods inherited from class org.apache.commons.validator.routines.checkdigit.ModulusCheckDigit

calculate, calculateModulus, getModulus, isValid, sumDigits, toCheckDigit, toInt

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

INSTANCE

public static final CheckDigit INSTANCE

Singleton Luhn Check Digit instance

POSITION_WEIGHT

private static final int[] POSITION_WEIGHT

weighting given to digits depending on their right position

Constructor Detail

LuhnCheckDigit

public LuhnCheckDigit()

Construct a modulus 10 Luhn Check Digit routine.

Method Detail

weightedValue

protected int weightedValue(int charValue,
                            int leftPos,
                            int rightPos)

Calculates the weighted value of a charcter in the code at a specified position.

For Luhn (from right to left) odd digits are weighted with a factor of one and even digits with a factor of two. Weighted values > 9, have 9 subtracted

Specified by:

weightedValue in class ModulusCheckDigit

Parameters:

charValue - The numeric value of the character.

leftPos - The position of the character in the code, counting from left to right

rightPos - The positionof the character in the code, counting from right to left

Returns:

The weighted value of the character.