Roman Numerals

import java.util.*;
import java.io.*;

public class RomanNumerals {
    public static void main(String[] args) throws IOException {
        testRomanNumerals();
        interactiveRomanNumerals();
    }

    private static void interactiveRomanNumerals() throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String input;
        String output;
        while ((input = br.readLine()) != null && input.length() > 0) {
            System.out.println(toRomanNumerals(input));
        }
    }

    private static String toRomanNumerals(String input) {
        String output;
        StringBuffer data = new StringBuffer(input).reverse();
        output = "";
        for (int i = 0; i < data.length(); i++) {
            output = getRomanNumeral(data.charAt(i), i) + output;
        }
        return output;
    }

    private static String getRomanNumeral(char value, int placeIdx) {
        String[][] romanChars = {
                {"I", "V", "X"},
                {"X", "L", "C"},
                {"C", "D", "M"},
                {"M", "?", "?"}
        };
        String one = romanChars[placeIdx][0];
        String five = romanChars[placeIdx][1];
        String ten = romanChars[placeIdx][2];

        switch (value - '0') {
            case 1:
                return one;
            case 2:
                return one + one;
            case 3:
                return one + one + one;
            case 4:
                return one + five;
            case 5:
                return five;
            case 6:
                return five + one;
            case 7:
                return five + one + one;
            case 8:
                return five + one + one + one;
            case 9:
                return one + ten;
            default:
                return "";
        }
    }

    private static void testRomanNumerals() {
        testEquals("I", toRomanNumerals("1"));
        testEquals("VI", toRomanNumerals("6"));
        testEquals("XXXI", toRomanNumerals("31"));
        testEquals("XXIV", toRomanNumerals("24"));
        testEquals("L", toRomanNumerals("50"));
        testEquals("CCCLXIX", toRomanNumerals("369"));
        testEquals("CD", toRomanNumerals("400"));
        testEquals("CDXLVIII", toRomanNumerals("448"));
        testEquals("MCMXCVIII", toRomanNumerals("1998"));
        testEquals("MMDCCLI", toRomanNumerals("2751"));
        System.out.println("All test cases passed.");
    }

    private static void testEquals(String left, String right) {
        if (!left.equals(right))
            throw new RuntimeException("Test failed. left != right (" + left + " != " + right + ")");
    }
}