Roman to integer java – Java program to Convert Roman Number to an Integer Number

Roman to integer java: In the previous article, we have seen Java Program to Reverse an Integer Number

In this article we will see how we can convert Roman numbers to an integer number by using Java programming language.

Java program to Convert Roman Number to an Integer Number

Approach:

  1. Create scanner class object.
  2. Take user input for the roman string.
  3. Initialize three variables result, prev and curr to 0.
  4. Scan the the string from end to start.
  5. Get the corresponding integer value from the user-defined method getValue() and check if it’s value is less than previous scanned roman character then subtract current value from the result else add it.
  6. Return the result.

Program:

import java.util.Scanner;

public class Main 
{

    public static void main(String[] args) 
    {
        // create scanner class object
        Scanner sc = new Scanner(System.in);
        // take input from user
        System.out.print("Enter a roman number: ");
        String roman = sc.nextLine();
        // convert roman to integer
        int result = romanToInt(roman);
        // print result
        System.out.println("Integer value: " + result);

    }

    //romanToInt() user defined method to convert roman number to integer
    private static int romanToInt(String roman) 
     {
        // declare variables
        int result = 0;
        int prev = 0;
        int curr = 0;
        // convert roman to integer
        for (int i = roman.length() - 1; i >= 0; i--) 
        {
            // get current and previous character
            curr = getValue(roman.charAt(i));
            if (curr < prev) 
            {
                result -= curr;
            } 
            else 
            {
                result += curr;
            }
            prev = curr;
        }
        return result;
    }

    private static int getValue(char charAt) 
    {
        switch (charAt) 
        {
            case 'I':
            case 'i':
                return 1;
            case 'V':
            case 'v':
                return 5;
            case 'X':
            case 'x':
                return 10;
            case 'L':
            case 'l':
                return 50;
            case 'C':
            case 'c':
                return 100;
            case 'D':
            case 'd':
                return 500;
            case 'M':
            case 'm':
                return 1000;
            default:
                return 0;
        }
    }
}
Output:

Case-1
Enter a roman number: II
Integer value: 2

Case-2
Enter a roman number: XI
Integer value: 11

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