RomanNumeralFormat
Sunday, March 15th, 2009Several years ago I wrote this RomanNumeralFormat class which extends java.text.NumberFormat but parses and formats Roman numerals. I just stumbled across it and thought it belonged here. This sort of thing should definitely be included in Java 7, then it will truly rule over Perl 6.
import java.text.FieldPosition;
import java.text.NumberFormat;
import java.text.ParseException;
import java.text.ParsePosition;
public class RomanNumeralFormat extends NumberFormat {
private static char[] roman_alpha = new char[] { 'M', 'D', 'C',
'L', 'X', 'V', 'I' };
private static int[] roman_num = new int[] { 1000, 500, 100, 50,
10, 5, 1 };
public StringBuffer format(double number, StringBuffer toAppendTo,
FieldPosition pos) {
// Too lazy
return null;
}
public StringBuffer format(long l, StringBuffer toAppendTo,
FieldPosition pos) {
StringBuffer buf = new StringBuffer(20);
while (l > 0) {
for (int i = 0; i < roman_num.length; i++) {
if (l >= roman_num[i]) {
buf.append(roman_alpha[i]);
l -= roman_num[i];
break;
} else {
int peek = i + 2 - (i % 2);
if (peek < roman_num.length) {
int j = roman_num[i] - roman_num[peek];
if (l >= j && j > 0) {
buf.append(roman_alpha[peek]);
buf.append(roman_alpha[i]);
l -= j;
break;
}
}
}
}
}
return buf;
}
public Number parse(String source, ParsePosition parsePosition) {
long l = 0;
int max = 0;
source = source.toUpperCase();
for (int i = source.length() - 1; i >= 0; i--) {
char c = source.charAt(i);
boolean validChar = false;
for (int j = 0; j < roman_alpha.length; j++) {
if (roman_alpha[j] == c) {
int k = roman_num[j];
if (k >= max) {
l += k;
max = k;
} else {
l -= k;
}
validChar = true;
break;
}
}
if (!validChar) {
parsePosition.setErrorIndex(i);
return null;
}
}
parsePosition.setIndex(source.length());
return new Long(l);
}
}
I was obviously pretty concerned about getting some large roman numerals through here – using a long rather than an int. Built to last.