チェックディジット (Modulus10 / Weight3) のサンプル

CheckDigitApp.java

package aoetk;

public class CheckDigitApp {

    public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Usage: java aoetk.CheckDigitApp target");
            System.exit(1);
        }
        try {
            System.out.println(getCheckDigit(args[0]));
        } catch (NumberFormatException e) {
            System.out.println("Argument is not a number.");
            System.exit(1);
        }
    }

    static String getCheckDigit(String target) throws NumberFormatException {
        int sum = 0;
        for (int i = 1; i <= target.length(); i++) {
            String digitStr = target.substring(target.length() - i, target.length() - i + 1);
            int digit = Integer.parseInt(digitStr);
            if (i % 2 == 0) {
                // 偶数位置は等倍
                sum += digit;
            } else {
                // 奇数位置は3倍
                sum += digit * 3;
            }
        }
        int mod = sum % 10;
        if (mod == 0) {
            return Integer.toString(0);
        } else {
            return Integer.toString(10 - mod);
        }
    }

}

CheckDigitAppTest.java

package aoetk;

import org.junit.Test;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

public class CheckDigitAppTest {

    @Test
    public void testGetCheckDigit_odd() throws Exception {
        String target = "351386327796";
        assertThat(CheckDigitApp.getCheckDigit(target), is("2"));
    }

    @Test
    public void testGetCheckDigit_even() throws Exception {
        String target = "51386327796";
        assertThat(CheckDigitApp.getCheckDigit(target), is("5"));
    }

}