Roman Numeral Converter

README.md

#Roman Numeral Converter#

###Usage### Using this class just requires an instance and calling of a function.

Roman->Numerical

Converter converter = new Converter();
System.out.println(converter.toNumerical("MDLXXXIV")); //1584

Numerical->Roman

Converter converter = new Converter();
System.out.println(converter.toRoman(1584)); //MDLXXXIV

isNumber() Used to check if a String is a number, helpful for validating user input.

int input = 10;
Converter converter = new Converter();
if(converter.isInt(input)) {
    System.out.println(converter.toRoman(input));
}else{
    System.out.println(converter.toNumerical(input));
}

Converter.java

package me.javersano.cs;

public class Converter {

    public final int[] NUMBER_VALUES = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 }; // array containing all of the values
    public final String[] NUMBER_LETTERS = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" }; // array containing all of the numerals

    /**
     * Method used to convert a string to a integer
     * @param roman roman numeral to be converted
     * @return integer
     */
    public int toNumerical(String roman) {
        for (int i : NUMBER_LETTERS) { // Loop through all the letters
            if(roman.startsWith(NUMBER_LETTERS[i])) // Check if the string starts with that letter
                return NUMBER_VALUES[i] + toNumerical(roman.replaceFirst(NUMBER_LETTERS[i], "")); // Rinse and repeats until the string is empty and return it
        }
        return 0; // If something went wrong, simply return 0
    }

    /**
     * Method used to convert a integer to a roman numeral
     * @param num number to be converted
     * @return roman numeral
     */
    public String toRoman(int num) {
        String roman = ""; // Declare a string to hold the numerals
        for (int i : NUMBER_VALUES) { // loop through all the values
            while (num >= NUMBER_VALUES[i]) { // Check if the number is greater than the current value
                roman += NUMBER_LETTERS[i]; // Add the letter to the String
                num -= NUMBER_VALUES[i]; // Subtract the amount from the value
            }
        }
        return roman; // Return the String
    }

    /**
     * Method used to check if a string is an integer
     * @param s string to be parsed
     * @return boolean
     */
    public boolean isInt(String s) {
        try {
            Integer.parseInt(s);
        }catch(NumberFormatException e) {
            return false;
        }
        return true;
    }

}

Just a quick comment! In your converter.java, you don't want a for each in line 28, but instead a normal for loop. After all, the index is important, and it's what you want to use inside the loop.

+1 @thyriki

check line 14. int i : number_letters. Int values in array of strings?