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Java regex: extraction function names

I am trying to extract a list of function names from a formula, but my regex is not working.

Considering ( aaa(111) + bbb(222) ) / ccc ( 333 )

I need to get an array of strings containing aaa

, bbb

and ccc

. Instead, I get aaa(

, bbb(

and ccc (

. how to do it?

This is my attempt:

    String formula = "( aaa(111) + bbb(222) ) / ccc ( 333 )";
    Pattern pattern = Pattern.compile("((\\w+)\\s*\\()");
    Matcher matcher = pattern.matcher(formula);

    while(matcher.find()){
        System.out.println(matcher.group(1));
    }
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2 answers


You have nested capturing groups, make the first non-capturing group:

Pattern pattern = Pattern.compile("(?:(\\w+)\\s*\\()");


or, as pointed out by Didier L , just remove the outer group:

Pattern pattern = Pattern.compile("((\\w+)\\s*\\(");
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There are 2 capture groups in your template:

  • outer brackets
  • those around \\w+

Since you are only interested in the second, you must either



  • take the second group: matcher.group(2)

  • remove the outer brackets:

    Pattern pattern = Pattern.compile("(\\w+)\\s*\\(");

Note that it matcher.group(0)

always matches the whole pattern (which is the equivalent of your outer brackets here)

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