Regex replace the substitution string

Question

Let's consider the following example:

String s = str.replaceAll("regexp", "$1");

Some languages allow us to specify \U$1 in place of $1 which converts matched groups with uppercase letters. How can I achieve the same using Java?

I know we can use Pattern class and get the group and convert it to uppercase, but that's not what I am looking for. I want to just change $1 with something that gets the job done.

I have also tried:

String s = str.replaceAll("regexp", "$1".toUpperCase());

But it looks like "$1".toUpperCase() is "$1" and not the match. I confirmed it using:

String s = str.replaceAll("regexp", method("$1"));

// method declared as method()
private static String method(String s) {
    System.out.println(s); // prints "$1"
    return s;
}

Is it even allowed in Java?

EDIT:

String s = "abc";
System.out.println(s.replaceAll("(a)", "$1")); // should print "Abc"

EDIT FOR POSSIBLE DUPE:

I am not looking for way using m.group(), is it possible using something like \U$1 in place of $1 with replaceAll()

To @Maroun, I know this won't be tagged to you but if you have read my question properly, you won't have marked this as a dupe. — user7780894
– user7780894, Commented Feb 3, 2018 at 12:01
The question is fairly simple, I am looking for concise version of doing it. — user7780894
– user7780894, Commented Feb 3, 2018 at 12:06

Eugene · Accepted Answer · 2018-02-04 14:14:10Z

2

\\U is not implemented in the java regex AFAIK and you can't do it with a regex as such (.NET has it IIRC). It's a bit verbose, but one way to do it would be:

    String test = "abc";
    Pattern p = Pattern.compile("(a)");
    Matcher m = p.matcher(test);

    StringBuilder sb = new StringBuilder();
    if (m.find()) {
        String match = test.substring(m.start(1), m.end(1));
        m.appendReplacement(sb, match.toUpperCase());
    }

    m.appendTail(sb);
    System.out.println(sb.toString());

answered Feb 4, 2018 at 14:14

Eugene

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Comments

Aniket Sahrawat · Accepted Answer · 2019-09-12 06:55:04Z

1

Since Java 9, we can provide a Function to Matcher#replaceAll(Function<MatchResult,String> replacer). It is more concise than other answers here. Eg:

Pattern.compile("regexp")
       .matcher(str)
       .replaceAll(mr -> mr.group().toUpperCase());

We can fully customize this behaviour since we have a hold on MatchResult:

Pattern.compile("regexp")
       .matcher(str)
       .replaceAll(mr -> {
                String.format("%s %s", 
                              mr.group(1).toUpperCase),
                              mr.group(2).indent(4);
                   });

edited Sep 12, 2019 at 6:55

answered Sep 12, 2019 at 6:15

Aniket Sahrawat

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Comments

Black.Jack · Accepted Answer · 2018-02-03 11:55:01Z

0

I think you should consider StringUtils from Apache Commons.

This is an example:

String s = "abcad";

String replacer = "a";

System.out.println(StringUtils.replaceChars(s, replacer, replacer.toUpperCase()));//<--AbcAd

Pls also consider this avoids you to implement the algorythm that necessarily will be under the hood, and the fact the every jar library introduced in a project is basically a new weak point.

This is maven dependency:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.7</version>
</dependency>

Hope it helps.

answered Feb 3, 2018 at 11:55

Black.Jack

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5 Comments

Black.Jack Over a year ago

Sure but the Op explicity doesn't want to use that approach.

user7780894 Over a year ago

If you did not notice, I posted the OP.

Black.Jack Over a year ago

yes, if u prefer you coul put your strings inside replace chars. that would be one line. So ? less than one line?

user7780894 Over a year ago

I don't understand, show me the code. What I think you mean to create at least two String objects in that case right?

Eugene Over a year ago

@roundAbout strings are immutable anyway, so you would create more instances anyway

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