Java code to convert any decimal number to any base

DecimalToAnyBaseConverter.java

import java.util.Stack;

public class DecimalToAnyBaseConverter {

    /*
        We use base 62 array for all base conversions
     */
    char[] base62 = new char[62];

    /*
    The constructor just initializes the char array
     */
    private DecimalToAnyBaseConverter() {
        //first the numbers
        for (int i = 0; i < 10; i++) {
            base62[i] = Character.forDigit(i, 10);
        }
        //next we do A through Z
        for (int i = 10; i < 36; i++) {
            base62[i] = (char) ('A' + i - 10);
        }
        //next we do a through z
        for (int i = 36; i < 62; i++) {
            base62[i] = (char) ('a' + i - 36);
        }
    }

    private String convert(int base, long decimal) {
        StringBuilder output = new StringBuilder();
        Stack<Long> stack = new Stack<>();
        while (true) {
            long div = decimal / base;
            long mod = decimal % base;
            stack.push(mod);
            if (div == 0) {
                break; //this is so smelly but i am rusty
            } else decimal = div;
        }
        while (!stack.isEmpty()) {
            output.append(base62[(int) stack.pop().longValue()]);
        }
        return output.toString();
    }

    public static void main(String[] args) {
        new DecimalToAnyBaseConverter().test();
        if (args.length != 2) {
            System.out.println("[Usage: java DecimalToAnyBaseConverter <base> <decimal>] where  base is a number <= 62 and decimal is a number < 9223372036854775807.");
            System.exit(-1);
        }
        try {
            int base = Integer.parseInt(args[0]);
            long decimal = Long.parseLong(args[1]);
            if (base > 62) throw new IllegalArgumentException("Base cannot be > 62.");
            System.out.println(new DecimalToAnyBaseConverter().convert(base, decimal));
        } catch (NumberFormatException e) {
            System.out.println("Usage Error: both arguments need to be valid numbers.");
            System.exit(-1);
        } catch (IllegalArgumentException e) {
            System.out.println("Usage Error: base cannot be > 62 [you provided " + args[0] + " ]");
            System.exit(-1);
        }
    }

    /*
    To run assertions pass -ea to the java command
     */
    private void test() {
        assert new DecimalToAnyBaseConverter().convert(62, 1024).equals("GW") : "Fail";
        assert new DecimalToAnyBaseConverter().convert(7, 10245500).equals("153041156") : "Fail";
        assert new DecimalToAnyBaseConverter().convert(8, 1024).equals("2000") : "Fail";
    }
}