Roman Numeral Conversion To Decimals

I have made a program that is supposed to convert roman numerals to decimals. It is NOT supposed to convert decimals to roman numerals. The only problem it seems there is with the program is that it only adds and does NOT subtract. This causes some roman numeral conversions to be flawed. What can I try to fix this. Keep in mind that the reason some methods exist is because the directions for the code say that I have to make it this way.

Instructions:

Write a program that converts a number entered in Roman numerals to decimal. Your program should consist of a class called Roman. An object of type Roman should be able to do the following:

1) Store the number as a Roman numeral.
2) Convert and store the number into decimal.
3) Print the number as a Roman numeral or decimal number as requested by the user. (Be sure to over-ride the toString function).
4) Your class must contain the method romanToDecimal to convert a Roman numeral into its equivalent decimal number.
5) Test your program using the following Roman numerals: MCXIV, CCCLIX, and MDCLXVI.

This is what I have so far. It compiles and there are no errors, but it does not subtract I from X, or I from V and so on. For example,CMXLVII should be 947, but the program outputs 1067.

import javax.swing.*;
import java.util.*;
public class Roman{
private String roman;
private int decimal;
public int romanToDecimal(String s)

[Code] .....