rootulp's solution

to ISBN Verifier in the Java Track

Published at May 28 2020 · 0 comments
Instructions
Test suite
Solution

The ISBN-10 verification process is used to validate book identification numbers. These normally contain dashes and look like: `3-598-21508-8`

ISBN

The ISBN-10 format is 9 digits (0 to 9) plus one check character (either a digit or an X only). In the case the check character is an X, this represents the value '10'. These may be communicated with or without hyphens, and can be checked for their validity by the following formula:

``````(x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + x10 * 1) mod 11 == 0
``````

If the result is 0, then it is a valid ISBN-10, otherwise it is invalid.

Example

Let's take the ISBN-10 `3-598-21508-8`. We plug it in to the formula, and get:

``````(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 == 0
``````

Since the result is 0, this proves that our ISBN is valid.

Given a string the program should check if the provided string is a valid ISBN-10. Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.

The program should be able to verify ISBN-10 both with and without separating dashes.

Caveats

Converting from strings to numbers can be tricky in certain languages. Now, it's even trickier since the check digit of an ISBN-10 may be 'X' (representing '10'). For instance `3-598-21507-X` is a valid ISBN-10.

• Generate a valid ISBN-13 from the input ISBN-10 (and maybe verify it again with a derived verifier).

• Generate valid ISBN, maybe even from a given starting ISBN.

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

``````\$ gradle test
``````

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the `@Ignore("Remove to run test")` annotation.

Source

Converting a string into a number and some basic processing utilizing a relatable real world example. https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

IsbnVerifierTest.java

``````import org.junit.Before;
import org.junit.Ignore;
import org.junit.Test;

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertFalse;

public class IsbnVerifierTest {
private IsbnVerifier isbnVerifier;

@Before
public void setUp() {
isbnVerifier = new IsbnVerifier();
}

@Test
public void validIsbnNumber() {
assertTrue(isbnVerifier.isValid("3-598-21508-8"));
}

@Ignore("Remove to run test")
@Test
public void invalidIsbnCheckDigit() {
assertFalse(isbnVerifier.isValid("3-598-21508-9"));
}

@Ignore("Remove to run test")
@Test
public void validIsbnNumberWithCheckDigitOfTen() {
assertTrue(isbnVerifier.isValid("3-598-21507-X"));
}

@Ignore("Remove to run test")
@Test
public void checkDigitIsACharacterOtherThanX() {
assertFalse(isbnVerifier.isValid("3-598-21507-A"));
}

@Ignore("Remove to run test")
@Test
public void invalidCharacterInIsbn() {
assertFalse(isbnVerifier.isValid("3-598-P1581-X"));
}

@Ignore("Remove to run test")
@Test
public void xIsOnlyValidAsACheckDigit() {
assertFalse(isbnVerifier.isValid("3-598-2X507-9"));
}

@Ignore("Remove to run test")
@Test
public void validIsbnWithoutSeparatingDashes() {
assertTrue(isbnVerifier.isValid("3598215088"));
}

@Ignore("Remove to run test")
@Test
public void isbnWithoutSeparatingDashesAndXAsCheckDigit() {
assertTrue(isbnVerifier.isValid("359821507X"));
}

@Ignore("Remove to run test")
@Test
public void isbnWithoutCheckDigitAndDashes() {
assertFalse(isbnVerifier.isValid("359821507"));
}

@Ignore("Remove to run test")
@Test
public void tooLongIsbnAndNoDashes() {
assertFalse(isbnVerifier.isValid("3598215078X"));
}

@Ignore("Remove to run test")
@Test
public void tooShortIsbn() {
assertFalse(isbnVerifier.isValid("00"));
}

@Ignore("Remove to run test")
@Test
public void isbnWithoutCheckDigit() {
assertFalse(isbnVerifier.isValid("3-598-21507"));
}

@Ignore("Remove to run test")
@Test
public void checkDigitOfXShouldNotBeUsedForZero() {
assertFalse(isbnVerifier.isValid("3-598-21515-X"));
}

@Ignore("Remove to run test")
@Test
public void emptyIsbn() {
assertFalse(isbnVerifier.isValid(""));
}

@Ignore("Remove to run test")
@Test
public void inputIsNineCharacters() {
assertFalse(isbnVerifier.isValid("134456729"));
}

@Ignore("Remove to run test")
@Test
public void invalidCharactersAreNotIgnored() {
assertFalse(isbnVerifier.isValid("3132P34035"));
}

@Ignore("Remove to run test")
@Test
public void inputIsTooLongButContainsAValidIsbn() {
assertFalse(isbnVerifier.isValid("98245726788"));
}
}``````
``````class IsbnVerifier {

private static final char VALID_CHECK_DIGIT = 'X';

/**
* Determine if the provided string is a valid ISBN according to the following formula
* (x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + x10 * 1) mod 11 == 0
*/
public static boolean isValidIsbn(String stringToVerify) {
String parsed = removeHyphens(stringToVerify);
if(!isValidParsed(parsed)) {
return false;
}

return computeValueForIsbn(parsed) % 11 == 0;
}

private static Integer computeValueForIsbn(String isbn) {
String reversed = new StringBuilder(isbn).reverse().toString();
int result = 0;
for (int i = 0; i < isbn.length(); i++) {
char c = reversed.charAt(i);
result += getValueFrom(c, i);
}
return result;
}

private static Integer getValueFrom(char c, int i) {
if(i == 0 && c == VALID_CHECK_DIGIT) {
return 10;
}
return Integer.parseInt(String.valueOf(c)) * (i + 1);
}

private static String removeHyphens(String s) {
return s.replaceAll("-", "");
}

private static boolean isValidParsed(String parsed) {
return isValidLength(parsed) &&
isValidCheckDigit(parsed.charAt((parsed.length() - 1))) &&
doesContainOnlyDigits(parsed.substring(0, parsed.length() - 1));
}

private static boolean isValidCheckDigit(char checkDigit) {
return Character.isDigit(checkDigit) || checkDigit == VALID_CHECK_DIGIT;
}

private static boolean isValidLength(String s) {
return s.length() == 10;
}

private static boolean doesContainOnlyDigits(String s) {
return s.codePoints().mapToObj(c -> (char) c).allMatch(c -> Character.isDigit(c));
}

public boolean isValid(String stringToVerify) {
return isValidIsbn(stringToVerify);
}
}``````