问我正在尝试循环一个数字并用另一种方法打印它。

EN

import java.util.Scanner;

public class Hw2 {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        diff here = new diff();
        String res;
        String d = "0";

        do {
            System.out.println("Enter 1 to enter length of number: ");
            System.out.println("q. quit: ");

            System.out.print("select:");
            res = in.next();
            in.nextLine();

            switch(res.charAt(0)) {
            case '1':
                // get n from user
                System.out.print("Enter the length of string: ");
                int n = in.nextInt();
                diff.printDecimal(n, d);
                break;
            case 'q': case 'Q':
                System.out.println("Bye!");
                break;
            default:
                System.out.println("Invalid");
                break;
            }
        } while (res.charAt(0) != 'q' && res.charAt(0) != 'Q');
    }
    }



class diff {

    // print string
    static void printDecimal (int n, String d) {
        String maxNum = "9";
        while( maxNum.length() < n ) {
            maxNum += 9;
        }
        while (d != maxNum) {
            System.out.println(inDecimal(n, d));
        }

    }

    // increase string value by 1
    static String inDecimal(int n, String d) {
        String d2 = "";
        int d3 = Integer.parseInt(d);
        d3++;
        d = Integer.toString(d3);
        //d = String.valueOf(d) + 1;
        while( d.length() < n ) {
            d2 = "0" + d;
            d = d2;
        }
        System.out.println(d);
        return d;
    }
}