Проверка ИНН на Java

Main.java

package main;

import java.util.regex.Pattern;

public class Main {

    public static void main(String[] args) {
        assert isValidINN("500100732259");
        assert isValidINN("7830002293");
        assert isValidINN(" 7830002293 ");
        assert !isValidINN("7830002294");
        assert !isValidINN("500100332251");
        assert !isValidINN("7830002294s");
        assert !isValidINN("78300022942");
        assert !isValidINN("  783000229");
    }

    private static final Pattern innPatter = Pattern.compile("\\d{10}|\\d{12}");
    public static boolean isValidINN(String inn) {
        inn = inn.trim();
        if (!innPatter.matcher(inn).matches()) {
            return false;
        }
        int length = inn.length();
        if (length == 12) {
            return INNStep(inn, 2, 1) && INNStep(inn, 1, 0);
        } else {
            return INNStep(inn, 1, 2);
        }
    }

    private static final int[] checkArr = new int[] {3,7,2,4,10,3,5,9,4,6,8};

    private static boolean INNStep(String inn, int offset, int arrOffset) {
        int sum = 0;
        int length = inn.length();
        for (int i = 0; i < length - offset; i++) {
            sum += (inn.charAt(i) - '0') * checkArr[i + arrOffset];
        }
        return (sum % 11) % 10 == inn.charAt(length - offset) - '0';
    }
}