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));
    }

Answer 1

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)