Rational number conversion to non decimal base

base.java

package com.company;

import java.util.Scanner;
import java.util.HashMap;

public class Main {

//  / n \
// | --- |
//  \ d /(b)

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);

        int n = s.nextInt(); // numerator
        int d = s.nextInt(); // denominator
        int b = s.nextInt(); // base

        int i_num = n / d;   // integer part
        int f_num = n % d;
        int f_den = d;

        Base e = new Base(b);
        String si = e.integer_base_convert(i_num);
        String sf = e.fractional_base_convert(f_num, f_den);


        System.out.println(si + "." + sf);
    }
}

class Base {
    // digits alphabet
    private static final String[] abc = {
              "0", "1", "2", "3", "4"
            , "5", "6", "7", "8", "9"
            , "a", "b", "c", "d", "e"
            , "f", "g", "h", "i", "j"
            , "k", "l", "m", "n", "o"
            , "p", "q", "r", "s", "t"
            , "u", "v", "w", "x", "y"
            , "z"
    };

    private int base;

    public Base(int b) {
        if (b > abc.length)
            throw new Error("Only bases up to "
                    + abc.length + " are supported");
        base = b;
    }
    public String integer_base_convert(int x) {
        StringBuilder ret = new StringBuilder();
        if (x == 0)
            return abc[0];
        while (x > 0) {
            ret.append(abc[x % base]);
            x /= base;
        }
        ret.reverse();
        return ret.toString();
    }

//
// let's find 5/12 in binary base
//                                    -------+     
//                                           |  
//    +-> 10/12    20/12     16/12      8/12 |   16/12 <-- we've already met "16" before
//    |                                      |                 so, we found the period 
//  5 |      10         8         4         8|         4           answer: 0.01(10)
// --*2= 0 + --*2= 1 + --*2= 1 + --*2= 0 + --*2= 1 + --*2=...
// 12    |   12    |   12    |   12    |   12|   |   12   
//       v         v         v         v     |   v        
// 0 .   0         1       ( 1         0 )   |   1         
//                                           |
//                                    -------+
//

    public String fractional_base_convert(int n, int d) {
        StringBuilder ret = new StringBuilder();
        int sch = 0;
        if (n >= d)
            n = n % d;
        if (n == 0)
            return abc[0];
        // state memory to search for periods
        HashMap<Integer, Integer> memory = new HashMap<>();
        while (true) {
            n *= base;
            if (memory.containsKey(n)) {
                int v = memory.get(n);
                // excluding cases like this: 54.321(0)
                if (sch - v <= 1 &&
                        ret.substring(ret.length()-1)
                                .equals(abc[0])) {
                    ret.setLength(ret.length() - 1);
                    break;
                }
                // 0.33333... => 0.(3)
                ret.append(")");
                ret.insert(v, "(");
                break;
            }
            memory.put(n, sch++);
            ret.append(abc[n / d]);
            n %= d;
        }
        return ret.toString();
    }
}