Roman Numerals. Could you point out my mistakes further down the road? - optimization

Question

Beginner here. This piece of code converts number into roman numerals in multiples of 50 if not 10 if not 9 and down to 0. Methods are so intertwined. Is there something (just at a glance) you could suggest I should avoid doing? Thank You.
public static void main(String[] args) {
System.out.println(fiftyAndAbove(37));
}
public static String nineAndDown(int number) {
String one = "I", five = "V", ten = "X", sum = "";
if(number == 5) {
return five;
} else if(number == 9) {
return one + ten;
}
else if(number > 5) {
for(int i=1; i<=number-5; i++) {
sum += one;
}
return five + sum;
} else {
if(number == 4 ) {
return one + five;
} else
for(int i=1; i <=number; i++) {
sum += one;
}
} return sum;
}
public static String tenAndAbove(int number) {
int remainder = number % 10, numberOftens = number/10;
String ten = "X", sum = "";
if(numberOftens > 0) {
while(numberOftens > 0) {
sum += ten;
numberOftens -= 1;
}
}
return sum + nineAndDown(remainder);
}
public static String fiftyAndAbove(int number) {
int remainder = number % 50, numberOfFifty = number/50;
String fifty = "L", sum = "";
if(numberOfFifty > 0) {
while(numberOfFifty > 0) {
sum += fifty;
numberOfFifty -= 1;
}
}
return sum + tenAndAbove(remainder);
}

Answer 1

Is there something (just at a glance) you could suggest I should avoid doing?
I'd not unnecessarily complicate the logic as with
if(numberOfFifty > 0) {
while(numberOfFifty > 0) {
…
}
}
which is equivalent to
while (numberOfFifty > 0)
{
…
}
You could also have a look at this implementation and see what you prefer:
import java.util.Arrays;
…
public static String fiftyAndAbove(int number)
{
int remainder = number%50, numberOfFifty = number/50;
char [] Ls = new char [numberOfFifty];
Arrays.fill(Ls, 'L');
return new String(Ls) + tenAndAbove(remainder);
}
You have four places like this in your program where you need a string of a character repeated. If you're willing to require a certain Java version or above, you can also use one of the methods described at Java: String - add character n-times; otherwise I'd suggest to use a function to do it.
You could also think about whether you find
String one = "I", five = "V", ten = "X", sum = "";
if(number == 5) {
return five;
} else if(number == 9) {
return one + ten;
}
really better than
if (number == 5) return "V";
if (number == 9) return "IX";