I need to find specific word on a string using regular expression. rules : before that word, I must not have a letter, a number or an underscore. this word must be not followed by a letter, a number or an underscore.

Example : I'm looking for the word 'the' in : 'Hi, it\'s a random text containing some words, the .the thingthe THE, tthe Tthe test_the@thesite.com'

in this string It must be found 3 times : the and .the and THE so I must get true as a return.

my code :

String str = 'Hi, it\'s a random text containing some words, the .the thingthe THE, tthe Tthe test_the@thesite.com';
String var = 'the';
String s = '(?<![\\w])'+var.toUpperCase()+'(?![\\w])';
Pattern MyPattern = Pattern.compile(s);
Matcher MyMatcher = MyPattern.matcher(str.toUpperCase());
System.debug('###matches : '+MyMatcher.matches());

Matches return always false. I tried with this also : '(?<![a-zA-Z0-9_])'+var.toUpperCase()+'(?![a-zA-Z0-9_])';

2 Answers 2


The matches method will only return true if the entire input string matches the result. You want to use find instead, which will match a substring. Take a look at the Matcher documentation for these methods:

  • find()
    Attempts to find the next subsequence of the input sequence that matches the pattern. This method returns true if a subsequence of the input sequence matches this Matcher object's pattern.
  • matches()
    Attempts to match the entire region against the pattern.

So if you want to know whether your substring is contained anywhere in the input string, use MyMatcher.find() instead.

A couple side notes:

  • If you want your expression to be case insensitive, set the i flag by starting your expression with (?i).
  • If you want to look for a whole word, wrap it in the word boundary character (\b), not backward and forward lookaheads for non-word characters.
  • With the above in mind, I would change the expression to: '(?i)\\b' + var + '\\b'

before that word, I must not have a letter, a number or an underscore.

A /W is supposed to match any character that is not a word character (alphanumeric & underscore) and is equivalent to (^A-Za-z0-9_).

That having been said, I think at the root of your issue is that you're using square brackets [\\W] in your code when apex is expecting parens (\\W) for your capture groups.

And as @Adrian Larson noted, you do need to use MyMatcher.find().

  • Square brackets vs parens is definitely not the issue here. They're not trying to capture the surrounding non-word characters, they're trying to specifically ignore them. Also I think you got the wrong slash before your W. ;)
    – Adrian Larson
    Dec 22, 2016 at 15:54
  • I looked at his code earlier and initially started to discuss non capture groups. He's using negative look aheads and negative look behinds rather than non-capture groups which would look like (?:\\W) NOT his (?<![\\w]) and (?![\\w]) which would seem to also be a problem. That would prevent him from finding what his IS looking for. The first slash needs to be escaped is why there's two. I don't believe it to be a forward slash, but I'd have to look at my apex code. The references show it as a backslash at regexr.com
    – crmprogdev
    Dec 22, 2016 at 16:02
  • Yeah as you've basically noted yourself the brackets are entirely extraneous. In fact, I think having any type of capturing group or lookahead/lookbehind is completely extraneous. In this case there's no real difference between (?:\W) and \W.
    – Adrian Larson
    Dec 22, 2016 at 16:04
  • Yes, exactly my point. His look aheads and behinds are preventing him from finding what he's looking for. When I initially read his question, I thought he was trying to find out what the look ahead and behind should be to find what to exclude to reveal what he wanted to find.
    – crmprogdev
    Dec 22, 2016 at 16:09
  • Have you tried the initial expression? It does work with find. It's inefficient, perhaps, but not flat out wrong. The matcher from the OP will find three groups.
    – Adrian Larson
    Dec 22, 2016 at 16:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.