Pass by reference in Java

I'm writing a program that converts roman numerals into a decimal number. The program ask the user to input a roman numeral and then ask if it wants to print it as a roman or decimal number. I've written this program in C++ and it ran perfectly. Now I have to translate it to java. The only program I am having is how to use pass by reference in java. Here is my code:

main.java

package romannumeralconverter;
import java.util.*;
import java.util.Scanner;

public class driver {
    public static void main(String[] args) {
        String roman = "";
        romanType newRoman = new romanType();
        newRoman.enterRoman();
        newRoman.storeRoman(roman);
        newRoman.convertToDecimal(roman);

        System.out.println("Which would you like to print: ");
        System.out.println("1. Roman");
        System.out.println("2. Decimal");
        int choice;
        Scanner scan = new Scanner(System.in);
        choice = scan.nextInt();
        if(choice == 1)
            newRoman.printRoman();
        else
            newRoman.printDecimal();
    }
}

romanType.java

package romannumeralconverter;
import java.util.*;

public class romanType {
    String roman;
    int integer;

    public void enterRoman(){
        System.out.println("Enter Roman Number: ");
    }
    public void storeRoman(String roman){
        Scanner input = new Scanner(System.in);
        roman = input.next();
    }
    public void convertToDecimal(String roman){
        int integerTotal = 0;
        int[] number = new int[10];
        int i = 0;
        while(i < roman.length()){
            switch(roman.length()){
                case 'M':
                    number[i] = 1000;
                    integerTotal += 1000;
                    break;
                case 'D':
                    number[i] = 500;
                    integerTotal += 500;
                    break;
                case 'C':
                    number[i] = 100;
                    integerTotal += 100;
                    break;
                case 'L':
                    number[i] = 50;
                    integerTotal += 50;
                    break;
                case 'X':
                    number[i] = 10;
                    integerTotal += 10;
                    break;
                case 'V':
                    number[i] = 5;
                    integerTotal += 5;
                    break;
                case 'I':
                    number[i] = 1;
                    integerTotal += 1;
                    break;
                default:
                    break;
            }

            for(int a = 0; a < roman.length()-1; a++){
                if(number[a] < number[a+1]){
                    integerTotal -= (number[a]*2);
                }
            }
            integer = integerTotal;
        }
    }
    public void printRoman(){
        System.out.println(roman);
    }
    public void printDecimal(){
        System.out.println(integer);
    }
}

in the method convertToDecimal, roman not set to anything so when I try to output the roman numeral as a decimal, it comes out to 0. What is the problem?