CodeIDの回答でマイナンバーDigit番号をチェックするコード
算出方法：https://codeiq.jp/sites/default/files/answer_ready/2007/mynumber.html

public class MyNmaber {

/**
 * 11,12桁半角数字
 */
private static final String CHECK_REGEX = "[0-9]{11,12}";


public static void main( String[] args ) throws IOException {

    int c;
    StringBuilder input = new StringBuilder();
    while ( ( c = System.in.read() ) != -1 ) {

        if ( c == 10 ) {

            checkMyNmber( input.toString() );
            input = new StringBuilder();
            continue;
        }

        input.append( (char) c );

    }

}


private static void checkMyNmber( String myNmber ) {

    if ( !Pattern.matches( CHECK_REGEX, myNmber ) ) {
        System.out.println( "Error" );
        return;
    }

    String checkDigit = calcDigit( myNmber.substring( 0, 11 ) );

    if ( myNmber.length() == 11 ) {
        System.out.println( checkDigit );
    } else {
        if ( checkDigit.equals( myNmber.substring( 11, 12 ) ) ) {
            System.out.println( "OK" );
        } else {
            System.out.println( "NG" );
        }

    }
}


private static String calcDigit( String number ) {

    int sum = 0;
    for ( int i = 1; i <= 11; i++ ) {

        int pn = Integer.valueOf( number.substring( 11 - i, 12 - i ) );
        int qn = i <= 6 ? i + 1 : i - 5;
        sum += pn * qn;
    }

    int mod = sum % 11;

    if ( mod <= 1 ) {
        return "0";
    } else {
        return String.valueOf( 11 - mod );

    }

}

}