Roman to integer

RomanToInteger.java

class Solution {
    private int symbolValue(char ch) {
        switch (ch) {
            case 'I':
                return 1;
            case 'V':
                return 5;
            case 'X':
                return 10;
            case 'L':
                return 50;
            case 'C':
                return 100;
            case 'D':
                return 500;
            case 'M':
                return 1000;
        }
        
        return 0;
    }
    
    public int romanToInt(String s) {
        int result = 0;
        int lastValue = 0;
        char[] chars = s.toCharArray();
        
        for (int i = chars.length - 1; i >= 0; i--) {
            int value = symbolValue(chars[i]);
            if (value < lastValue) {
                result -= value;
            } else {
                result += value;
            }
            
            lastValue = value;
        }
        
        return result;
    }
}