Java regex: extract function names

Question

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

Given ( aaa(111) + bbb(222) ) / ccc ( 333 ) I need to obtain an array of strings containing aaa, bbb and ccc. Instead, I'm getting aaa(, bbb( and ccc (. how to make this work?

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));
    }

Looks like you'll need a parser. You haven't specified the exact rules, but a regex generally isn't powerful enough to do this. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Apr 28, 2015 at 23:18

Didier L · Accepted Answer · 2015-04-28 23:21:34Z

2

You have 2 capturing groups in your pattern:

the external parentheses
the ones around \\w+

Since you are only interested in the second one, you should either

take the second group: matcher.group(2)

remove the external parentheses:

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

Notice that matcher.group(0) is always the match of the whole pattern (so equivalent to your external parentheses here)

answered Apr 28, 2015 at 23:21

Didier L

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Community · Accepted Answer · 2017-05-23 11:51:11Z

0

You've got nested capture groups, make the first one a non-capture 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*\\(");

edited May 23, 2017 at 11:51

CommunityBot

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answered Apr 28, 2015 at 23:19

adamdc78

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