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Description
given a Roman numerical, convert it to an integer.
input is guaranteed to be within the range from 1 to 3999.
analysis
scan from front to back, record the segment number with a temporary variable
if the current value is larger than the previous one, the value of this segment should be the current value minus the previous one. For example, IV = 5 – 1; If not, add the current value to the result and start the next record. For example, VI = 5 + 1, II = 1 + 1
code

 1 public class RomanToInteger {
 2 
 3     public static void main(String[] args) {
 4         // TODO Auto-generated method stub
 5         String roman = "CLXXXVII";
 6         System.out.println(romanToInteger2(roman));
 7     }
 8 
 9     public static int romanToInteger(String roman) {
10         // int num=0;
11         // int radix[] = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };
12         // String symbol[] = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX",
13         // "V", "IV", "I" };
14         if (roman.length() > 0) {
15             if (roman.charAt(0) == 'M') {
16                 roman = roman.substring(1);
17                 return 1000 + romanToInteger(roman);
18             }
19             if (roman.contains("CM")) {
20                 roman = roman.substring(2);
21                 return 900 + romanToInteger(roman);
22             }
23             if (roman.charAt(0) == 'D') {
24                 roman = roman.substring(1);
25                 return 500 + romanToInteger(roman);
26             }
27             if (roman.contains("CD")) {
28                 roman = roman.substring(2);
29                 return 400 + romanToInteger(roman);
30             }
31             if (roman.charAt(0) == 'C') {
32                 roman = roman.substring(1);
33                 return 100 + romanToInteger(roman);
34             }
35             if (roman.contains("XC")) {
36                 roman = roman.substring(2);
37                 return 90 + romanToInteger(roman);
38             }
39             if (roman.charAt(0) == 'L') {
40                 roman = roman.substring(1);
41                 return 50 + romanToInteger(roman);
42             }
43             if (roman.contains("XL")) {
44                 roman = roman.substring(2);
45                 return 40 + romanToInteger(roman);
46             }
47             if (roman.charAt(0) == 'X') {
48                 roman = roman.substring(1);
49                 return 10 + romanToInteger(roman);
50             }
51             if (roman.contains("IX")) {
52                 roman = roman.substring(2);
53                 return 9 + romanToInteger(roman);
54             }
55             if (roman.charAt(0) == 'V') {
56                 roman = roman.substring(1);
57                 return 5 + romanToInteger(roman);
58             }
59             if (roman.contains("IV")) {
60                 roman = roman.substring(2);
61                 return 4 + romanToInteger(roman);
62             }
63             if (roman.charAt(0) == 'I') {
64                 roman = roman.substring(1);
65                 return 1 + romanToInteger(roman);
66             }
67         }
68         return 0;
69     }

Here is the method without recursion (Reprint)

 1 private static int map(char c) {
 2         switch (c) {
 3         case 'I':
 4             return 1;
 5         case 'V':
 6             return 5;
 7         case 'X':
 8             return 10;
 9         case 'L':
10             return 50;
11         case 'C':
12             return 100;
13         case 'D':
14             return 500;
15         case 'M':
16             return 1000;
17         default:
18             return 0;
19         }
20     }
21 
22     public static int romanToInteger2(String s) {
23         int result = 0;
24         char[] sch = s.toCharArray();
25         for (int i = 0; i < sch.length; i++) {
26             if (i > 0 && map(sch[i]) > map(sch[i - 1])) {
27                 result += (map(sch[i]) - 2 * map(sch[i - 1]));
28             } else {
29                 result += map(sch[i]);
30             }
31         }
32         return result;
33     }