public static String ArabicToRoman(int aNumber){

        if(aNumber < 1 || aNumber > 3999){
            return "-1";
        }

        int[] aArray = {1000,900,500,400,100,90,50,40,10,9,5,4,1};
        String[] rArray = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
        String rNumber = "";
        
        for(int i=0; i<aArray.length; i++){
            while(aNumber >= aArray[i]){
                rNumber += rArray[i];
                aNumber -= aArray[i];
            }
        }

        return rNumber;
    }

Arabic to Roman numerals

Java