How to modify this regular expression to be case insensitive while searching for curse words?

Question

At the moment, this profanity filter finds darn and golly but not Darn or Golly or DARN or GOLLY.

List<String> bannedWords = Arrays.asList("darn", "golly", "gosh");

StringBuilder re = new StringBuilder();
for (String bannedWord : bannedWords)
{
    if (re.length() > 0)
        re.append("|");
    String quotedWord = Pattern.quote(bannedWord);
    re.append(quotedWord);
}

inputString = inputString.replaceAll(re.toString(), "[No cursing please!]");

How can it be modified to be case insensitive?

RegEx isn't the most efficient way to find a substring occurrence. If performance matters in this case, there are a number of more efficient substring matching algorithms http://en.wikipedia.org/wiki/String_searching_algorithm — Eric J., Oct 10 '11 at 20:06
You probably also want to learn about `\b` to avoid making another clbuttic mistake. — Donal Fellows, Oct 10 '11 at 20:07

score 3 · Answer 1 · answered Oct 10 '11 at 19:59

3

Start the expression with (?i).

I.e., change re.toString() to "(?i)" + re.toString().

From the documentation of Pattern

(?idmsux-idmsux) Nothing, but turns match flags i d m s u x on - off

where i is the CASE_INSENSITIVE flag.

answered Oct 10 '11 at 19:59

aioobe

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Teaching aix something... that should be a silver or gold badge ;-) – aioobe Oct 10 '11 at 20:03

score 3 · Answer 2 · edited May 23 '17 at 10:34

3

You need to set the CASE_INSENSITIVE flag, or simply add (?i) to the beginning of your regex.

StringBuilder re = new StringBuilder("(?i)");

You'll also need to change your conditional to

if (re.length() > 4)

Setting the flag via @ratchetFreak's answer is probably best, however. It allows for your condition to stay the same (which is more intuitive) and gives you a clear idea of what's going on in the code.

For more info, see this question and in particular this answer which gives some decent explanation into using regex's in java.

edited May 23 '17 at 10:34

Community

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answered Oct 10 '11 at 20:00

brc

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Beware of the `if (re.length() > 0)` condition. – aioobe Oct 10 '11 at 20:01

score 1 · Accepted Answer · answered Oct 10 '11 at 20:04

1

use a precompiled java.util.regex.Pattern

Pattern p = Pattern.compile(re.toString(),Pattern.CASE_INSENSITIVE);//do this only once

inputString = p.matcher(inputString).replaceAll("[No cursing please!]");

answered Oct 10 '11 at 20:04

ratchet freak

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How to modify this regular expression to be case insensitive while searching for curse words?

3 Answers3