ArrayIndexOutOfBoundsException Error in Program

I'm coding a program that converts roman numerals into numbers. I've gotten to a certain point in my code where it keeps on showing the error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2
    at RomanNums.<init>(RomanNums.java:80)
    at RomanNums.main(RomanNums.java:5)

Here is the code at which the problem occurs:

int num = IBIO.inputInt ("Which Roman Numeral would you like to convert? ");

        int conv = 0;
        //I for 1, V for 5, X for 10, L for 50, C for 100, D for 500, and M for 1000
        if (num == 1){
            for (int i = 0 ; i<n1.length ; i++)
            {

                if (n1[i]== 'I'){
                    if (n1[i+1] == 'V'){
                        conv+=4;
                        i++;
                    }
                    else if (n1[i+1] == 'X'){
                        conv+=9;
                        i++;
                    }
                    else
                        conv++;
                }
                if (n1[i] == 'V')
                    conv+=5;
                if (n1[i] == 'X'){
                    if (n1[i+1] == 'L'){
                        conv+=40;
                        i++;
                    }
                    else if (n1[i+1] == 'C'){
                        conv+=90;
                        i++;
                    }
                    else
                        conv+=10;
                }
                if (n1[i] == 'L')
                    conv+=50;
                if (n1[i] == 'C'){
                    if (n1[i+1] == 'D'){
                        conv+=400;
                        i++;
                    }
                    else if (n1[i+1] == 'M'){
                        conv+=900;
                        i++;
                    }
                    else
                        conv+=100;
                }
                if (n1[i] == 'D')
                    conv+=500;
                if (n1[i] == 'M')
                    conv+=1000;
            }
    }

When I run the whole program works fine but once I input the number into int num, it doesn't work