How to Convert a Integer Number to Roman Using Java ?

Roman Numbers :

Its a numeric system used to express numbers by using combinations of different Latin alphabets in ancient Rome. Some time this numeric system is still used.

No zero in Roman Number :

Roman numeric system don't have Zero (o) . So its always start with 1. Also it does not have negative values like modern decimal system.

Largest number which can express in Roman:

The maximum integer value which can be written in form of Roman numeric system is 3888. 3888 can be expressed in Roman as MMMDCCCLXXXVIII. This is because M,C and X can be used maximum of three times but this can't be done with D, L and V.
However roman uses bar over letters to express times thousand.
__
VI = 6000
So
__________________
MMMDCCCLXXXVIII = 3888000 could be largest but we will consider 3888 as largest Roman number in our code.

Java Code to Convert Integer to Roman Numbers

package myapps;

/**
 *
 * @author JavaTalk.org
 */
public class RomanConverter {
    
    
    public static void main(String arg[])
    {
        RomanConverter rc=new RomanConverter();
        
        for (int i=1 ; i<=100;i++)
        {
        System.out.println(i+"\t--->\t"+rc.Decimal2Roman(i));
        }
        
    }
   
    public  String Decimal2Roman(int num) {

    String[] romValues = {"M","XM","CM","D","XD","CD","C","XC","L","XL","X","IX","V","IV","I"};
    int[] integerValues = {1000, 990, 900, 500, 490, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
    
    StringBuilder result = new StringBuilder();
    
    int i = 0;
    if(num>3888)
    {
        System.out.println("Please Enter lesser number");
        return null;
    }
    
    if(num<=0)
    {
        System.out.println("Please Enter number greater than Zero");
        return null;
    }
    
    
    
    while (num > 0) 
    {
        while ((num - integerValues[i]) >= 0) 
        {
            num = num - integerValues[i];
            result.append(romValues[i]);
        }
        i++;
    }
    return result.toString();
}
    
}

Output of Program is :

Roman Numbers from 1 to 100

1 ---> I
2 ---> II
3 ---> III
4 ---> IV
5 ---> V
6 ---> VI
7 ---> VII
8 ---> VIII
9 ---> IX
10 ---> X
11 ---> XI
12 ---> XII
13 ---> XIII
14 ---> XIV
15 ---> XV
16 ---> XVI
17 ---> XVII
18 ---> XVIII
19 ---> XIX
20 ---> XX
21 ---> XXI
22 ---> XXII
23 ---> XXIII
24 ---> XXIV
25 ---> XXV
26 ---> XXVI
27 ---> XXVII
28 ---> XXVIII
29 ---> XXIX
30 ---> XXX
31 ---> XXXI
32 ---> XXXII
33 ---> XXXIII
34 ---> XXXIV
35 ---> XXXV
36 ---> XXXVI
37 ---> XXXVII
38 ---> XXXVIII
39 ---> XXXIX
40 ---> XL
41 ---> XLI
42 ---> XLII
43 ---> XLIII
44 ---> XLIV
45 ---> XLV
46 ---> XLVI
47 ---> XLVII
48 ---> XLVIII
49 ---> XLIX
50 ---> L
51 ---> LI
52 ---> LII
53 ---> LIII
54 ---> LIV
55 ---> LV
56 ---> LVI
57 ---> LVII
58 ---> LVIII
59 ---> LIX
60 ---> LX
61 ---> LXI
62 ---> LXII
63 ---> LXIII
64 ---> LXIV
65 ---> LXV
66 ---> LXVI
67 ---> LXVII
68 ---> LXVIII
69 ---> LXIX
70 ---> LXX
71 ---> LXXI
72 ---> LXXII
73 ---> LXXIII
74 ---> LXXIV
75 ---> LXXV
76 ---> LXXVI
77 ---> LXXVII
78 ---> LXXVIII
79 ---> LXXIX
80 ---> LXXX
81 ---> LXXXI
82 ---> LXXXII
83 ---> LXXXIII
84 ---> LXXXIV
85 ---> LXXXV
86 ---> LXXXVI
87 ---> LXXXVII
88 ---> LXXXVIII
89 ---> LXXXIX
90 ---> XC
91 ---> XCI
92 ---> XCII
93 ---> XCIII
94 ---> XCIV
95 ---> XCV
96 ---> XCVI
97 ---> XCVII
98 ---> XCVIII
99 ---> XCIX
100 ---> C

Please comment if you have any better method or code.