How to Find Commas Outside Parentheses Using Regex in Java?

Matching Commas Outside Parentheses with Regex

Matching specific patterns in text is a common task in programming, particularly when working with text files or user inputs. In this instance, the objective is to find all commas in a string that are not enclosed within parentheses.

Using Java regular expressions, one can craft a regex pattern to achieve this goal. The provided regex is:

Pattern regex = Pattern.compile(
    ",         # Match a comma\n" +
    "(?!       # only if it's not followed by...\n" +
    " [^(]*    #   any number of characters except opening parens\n" +
    " \)      #   followed by a closing parens\n" +
    ")         # End of lookahead", 
    Pattern.COMMENTS);

This pattern breaks down as follows:

• ", matches a comma.
• (?! starts a negative lookahead assertion.
• [^(]* matches any number of characters except opening parentheses.
• \) matches a closing parenthesis.
• ) ends the negative lookahead assertion.

The negative lookahead ensures that the current comma is not followed by a closing parenthesis. This effectively excludes commas within parentheses.

In Java, the Pattern class can be used to compile and match regex patterns. The compiled pattern can then be used to identify matching substrings in the input string.

Example usage:

String input = "12,44,foo,bar,(23,45,200),6";
Matcher matcher = regex.matcher(input);
while (matcher.find()) {
    System.out.println(matcher.group());
}

This code will print the commas that are not inside parentheses, as specified by the regex:

,
,
,

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