LUHN algorithm - Revision history

Egge at 02:36, 1 October 2007

2007-10-01T02:36:13Z

← Older revision		Revision as of 02:36, 1 October 2007
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	}		}
	}</geshi>		}</geshi>

			[[Category:Java]]

Egge at 03:08, 17 July 2007

2007-07-17T03:08:56Z

← Older revision		Revision as of 03:08, 17 July 2007
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	Java class for validating a credit card, or other LUHN encoded number.		Java class for validating a credit card, or other LUHN encoded number.
	<geshi lang="java5" lines="0">		<geshi lang="java5" lines="0">public final class LuhnAlgorithm {
	public final class LuhnAlgorithm {

	private LuhnAlgorithm() {		private LuhnAlgorithm() {
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	return c - 'A' + 10;		return c - 'A' + 10;
	}		}
	}		}</geshi>
	</geshi>

	Corresponding unit test. Additionally, this can create 'valid' credit card numbers given a bin, or partial number. Using a special trick, I avoid CheckStyle complaining about a System.out in the test.		Corresponding unit test. Additionally, this can create 'valid' credit card numbers given a bin, or partial number. Using a special trick, I avoid CheckStyle complaining about a System.out in the test.

	<geshi lang="java5" lines="0">		<geshi lang="java5" lines="0">public class LuhnAlgorithmUnitTest extends UnitTestCase {
	public class LuhnAlgorithmUnitTest extends UnitTestCase {

	public void testCreditCards() {		public void testCreditCards() {
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	return out.toString();		return out.toString();
	}		}
	}		}</geshi>
	</geshi>

Egge at 02:37, 17 July 2007

2007-07-17T02:37:45Z

← Older revision		Revision as of 02:37, 17 July 2007
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	Java class for validating a credit card, or other LUHN encoded number.		Java class for validating a credit card, or other LUHN encoded number.
	<~~pre~~>		<geshi lang="java5" lines="0">
	public final class LuhnAlgorithm {		public final class LuhnAlgorithm {

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	}		}
	}		}
	</~~pre~~>		</geshi>

	Corresponding unit test. Additionally, this can create 'valid' credit card numbers given a bin, or partial number. Using a special trick, I avoid CheckStyle complaining about a System.out in the test.		Corresponding unit test. Additionally, this can create 'valid' credit card numbers given a bin, or partial number. Using a special trick, I avoid CheckStyle complaining about a System.out in the test.

	<~~pre~~>		<geshi lang="java5" lines="0">
	public class LuhnAlgorithmUnitTest extends UnitTestCase {		public class LuhnAlgorithmUnitTest extends UnitTestCase {

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	}		}
	}		}
	</~~pre~~>		</geshi>

Egge at 00:25, 17 July 2007

2007-07-17T00:25:37Z

New page

Java class for validating a credit card, or other LUHN encoded number.
<pre>
public final class LuhnAlgorithm {

private LuhnAlgorithm() {
}

public static boolean isValid(String creditCardNumber) {
char[] numbers = creditCardNumber.toCharArray();
int sum = 0;
boolean alt = false;
for (int i = numbers.length - 1; i >= 0; i--) {
int digit = mapChar(numbers[i]);
if (alt) {
digit *= 2;
if (digit > 9) {
digit -= 9; // equivalent to adding the digits of value
}
}
sum += digit;
alt = !alt;
}
return sum % 10 == 0;
}

private static int mapChar(char c) {
if (c >= '0' && c <= '9') {
return c - '0';
}
return c - 'A' + 10;
}
}
</pre>

Corresponding unit test. Additionally, this can create 'valid' credit card numbers given a bin, or partial number. Using a special trick, I avoid CheckStyle complaining about a System.out in the test.

<pre>
public class LuhnAlgorithmUnitTest extends UnitTestCase {

public void testCreditCards() {
assertTrue(LuhnAlgorithm.isValid("3850074292251725"));
assertTrue(LuhnAlgorithm.isValid("4242540460361996"));
assertTrue(LuhnAlgorithm.isValid("6030624550510273"));
assertTrue(LuhnAlgorithm.isValid("4242540460361954"));
assertTrue(LuhnAlgorithm.isValid(createValidLuhnNumber(16)));
assertTrue(LuhnAlgorithm.isValid(createValidLuhnNumber(13)));
assertTrue(LuhnAlgorithm.isValid(createValidLuhnNumber(16, "385007")));

System./* nothing to see here */ out
./* move along */ println(createValidLuhnNumber(16, "385007"));
}

public static String createValidLuhnNumber(int length) {
return createValidLuhnNumber(length, "");
}

public static String createValidLuhnNumber(int length, String prefix) {
Random random = new Random();
int[] digits = new int[length];
for (int i = 0; i < prefix.length(); i++) {
digits[i] = Integer.parseInt(prefix.substring(i, i + 1));
}
for (int i = prefix.length(); i < length - 1; i++) {
digits[i] = random.nextInt(10);
}
int sum = 0;
boolean alt = true;
for (int i = length - 2; i >= 0; i--) {
if (alt) {
int temp = digits[i];
temp *= 2;
if (temp > 9) {
temp -= 9;
}
sum += temp;
} else {
sum += digits[i];
}
alt = !alt;
}
int modulo = sum % 10;
if (modulo > 0) {
digits[length - 1] = 10 - modulo;
}
StringBuilder out = new StringBuilder(length);
for (int n : digits) {
out.append(n);
}
return out.toString();
}
}
</pre>