Pattern.matcher(s).replaceAll(“$1$2$3”) Transform only $2 to lowercase

Question

I have a String like this

final String text = "Some Text #AAAA some Other text .." (# with 4 uppercase letters)

Pattern patt = Patter.compile("(.*?)(#)([A-Z]{4})(.*?)");
patt.matcher(text ).replaceAll("$1$3$4")

remove only the # in text

I would have AAAA in lowercase, result expected :

Some Text aaaa some Other text ..

How have this result in lower case, only for the four AAAA ?

Answer 1

Rather than use replaceAll directly you'll have to do the appendReplacement loop yourself. I would use a simpler regex:

Pattern patt = Patter.compile("#([A-Z]{4})");
Matcher mat = patt.matcher(text);
StringBuffer buf = new StringBuffer();
while(mat.find()) {
  mat.appendReplacement(buf, mat.group(1).toLowerCase());
}
mat.appendTail(buf);

Normally you have to watch out with appendReplacement (and replaceAll ) and use Matcher.quoteReplacement if the replacement string might contain $ signs or backslashes, but in this case we know that can't happen as group 1 will always be exactly four letters.

Answer 2

This will work:

Matcher matcher = patt.matcher(text);
matcher.matches();
String res = matcher.group(1) + matcher.group(3).toLowerCase() + matcher.group(4);

Answer 3

here is an oneliner:

String text2 = text.replaceFirst("(?<=#)[A-Z]{4}", text.replaceAll(".*?#([A-Z]{4}).*", "$1").toLowerCase());

take your example:

final String text = "Some Text #AAAA some Other text ..";
        String text2 = text.replaceFirst("(?<=#)[A-Z]{4}", text.replaceAll(".*?#([A-Z]{4}).*", "$1").toLowerCase());
        System.out.println(text2);

will output:

Some Text #aaaa some Other text ..

Answer 4

Try this :

public static void main (String args[]) {
    String matched = "";
    Pattern pattern = Pattern.compile("(.*?)(#)([A-Z]{4})(.*?)");
    Matcher matcher = pattern.matcher("Some Text #AAAA some Other text");
    if (matcher.find()) {   
        matched =  matcher.group(1) + matcher.group(3).toLowerCase() + matcher.group(4);
    }
    System.out.println(matched);
}

Answer 5

Quote from the Matcher.replaceAll() API page :

Note that backslashes ( \\ ) and dollar signs ( $ ) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Dollar signs may be treated as references to captured subsequences.

This sounds exactly like the problem you're facing...