Replace All string with Regex in the replacement string?

Question

Here is the text

<some string here could contain W or L letter><W1>123<W2>123<W3>123.

I hope to replace

<W(number)>

pattern to

<L(number)>

pattern.

String str = "<WLWLWL><W1><FS>123<W2><FS>345<E>";
    System.out.println(str);

    Pattern p = Pattern.compile("<[A-Z]\\d>");
    Matcher m = p.matcher(str);

    while(m.find()){
        System.out.println(m.group());
    }

    str.replaceAll("<[A-Z]\\d>", "<L\\d>");
    System.out.println(str);

I can find exactly what I want with code above but the replace is not working.

I suppose the replace string doesn't take the regex in it. So what's the best way to do it?

What is not working with your replace? Does it throw an error? (If yes, please [edit] the question and add the stacktrace.) Does it produce some unexpected result? (If yes, please [edit] the question and add your expected and actual output). It it something else? [edit] the question and don't make me guess what is wrong. — Johannes Kuhn, Sep 03 '19 at 22:49

score 3 · Answer 1 · answered Sep 03 '19 at 22:53

3

I think you're looking for a capturing group:

str = str.replaceAll("<[A-Z](\\d)>", "<L$1>");

Note the assignment at the beginning. replaceAll() doesn't modify the string (strings are immutable); it returns a new one.

answered Sep 03 '19 at 22:53

shmosel

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Use `group()` or `group(0)` to get the full match. – shmosel Sep 04 '19 at 16:43

Yoshikage Kira · Accepted Answer · 2019-09-03T23:25:17.273

Another alternative you can try is to use regex look around.

str = str.replaceAll("[a-zA-Z](?=\\d)", "L");

RegEx explanation:

[a-zA-Z](?=\\d)    finds the letter within (a-zA-Z) which has a number after it

Output:

<WLWLWL><L1><FS>123<L2><FS>345<E>

Source: Regex lookahead, lookbehind and atomic groups

Replace All string with Regex in the replacement string?

2 Answers2