Find position and insert characters

Introduction:

I was working on formatting wrongly entered numberplates of a car. One business rule was to format all of them in the right perspective. Like 11aa33 should be 11-AA-33. But how to find out where to put the minusses.

The solution

 First of all make sure you only have capitals like:

numberplate.toUpperCase();

This takes care of all the characters in the numberplate.

The second step is:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.commons.lang.StringUtils;

    private static final String MINUS = "-";
    private static final String DIGIT_MATCH = "[0-9]{1,3}";
    private static final String CHARACTER_MATCH = "[A-Z]{1,3}";

        String formatted = kenteken;
//counting the right amount of minusses.

if (StringUtils.countMatches(kenteken, MINUS) != 2) {

           //the actual patterns to find
            Pattern digitPattern = Pattern.compile(DIGIT_MATCH);
            Pattern charsPattern = Pattern.compile(CHARACTER_MATCH);

          // find the matches
            Matcher digitMatcher = digitPattern.matcher(formatted);
            Matcher charsMatcher = charsPattern.matcher(formatted);
            

             // adding the minusses

            if (digitMatcher.find()) {
                formatted = new StringBuffer(formatted).insert(
                        digitMatcher.end(), MINUS).toString();
            }
            if (charsMatcher.find()) {
                formatted = new StringBuffer(formatted).insert(
                        charsMatcher.end(), MINUS).toString();
            }
        }

        return formatted;

Have fun!