Java Regex won't match, any explanations?

Question

The regex String :

"[Ff][uU][Nn][Cc] "

Matches input:

"fUnC "

But not:

"func across( a, b )"

And I don't understand why...

I'm testing my expressions here: http://www.regexplanet.com/simple/index.html

I figured out that I (dumbly) needed my regex to be "[Ff][uU][Nn][Cc] .*" for a match.

SOLVED: Don't use the convenience method Pattern.Matches(regex, input) if you are looking for what amounts to a submatch. You should use the Matcher.find() method instead.

I'm not trying to match the whole string, just testing that the symbol "func " can be detected in the string. — avgvstvs, Apr 25 '11 at 00:47
That would be cleaner, but that didn't work. Using the test site (and my own code) the only way to score a match was with `.*` at the end. — avgvstvs, Apr 25 '11 at 00:56
Java's `Pattern.Matches(regex, input)` apparently tries to match only the entire string. Also, you can't set flags when using Pattern.Matches, so I didn't bother with case-insensitive. — avgvstvs, Apr 25 '11 at 00:58
I was using the convenience method `Pattern.Matches(regex, input)` which uses the matches. I learned through this that Matches goes for the whole line, find looks for substrings. Not how I'm used to doing things, but it works now... — avgvstvs, Apr 25 '11 at 01:11
As you see, Java’s `matches` method is rather more of an **inconvenience method** than a convenience one. :) You’re hardly the first one to get tripped up by Java’s bizarre redefinition of the word *matches.* There are [plenty of other gotchas](http://stackoverflow.com/questions/5767627/java-regex-helper/5771326#5771326), too. :( — tchrist, Apr 25 '11 at 02:30

score 4 · Accepted Answer · answered Apr 25 '11 at 00:52

4

When I use the regex tester you link to, I see that your regex works with find(), but not with matches(). This is what I would expect -- find() just looks for a regex hit within the target string, while matches() always tries to match the entire string.

answered Apr 25 '11 at 00:52

njudge

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No way to learn that like the hard way, lol. I'll alter the code. – avgvstvs Apr 25 '11 at 01:01

score 0 · Answer 2 · answered Apr 25 '11 at 00:50

0

"[Ff][uU][Nn][Cc].*" may help...

answered Apr 25 '11 at 00:50

Vicente Plata

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It should match without the `.*`, since `func ` matches the pattern. – Rafe Kettler Apr 25 '11 at 00:52
My mistake was in forgetting that matches are lazy. Sure, I might match part of the string, but not all of it. I have it working now... – avgvstvs Apr 25 '11 at 00:55
Yes. But 'func across...' doesn't. – Vicente Plata Apr 25 '11 at 00:55

score 0 · Answer 3 · answered Apr 25 '11 at 00:53

0

It can be.... it's working fine. But your strings in there and you'll see MATCHES is false, but replaceFirst and ReplaceAll work fine.

If you want MATCHES to be true

add a * at the end

answered Apr 25 '11 at 00:53

MJB

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score 0 · Answer 4 · answered Apr 25 '11 at 00:57

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Have you also tried using the regex tester, ignoring case? There should be a way to turn on case insensitivity in the Java regex matcher.

answered Apr 25 '11 at 00:57

jefflunt

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Not when using the convenience method `Pattern.Matches(regex, input)`. You only can use those flags when doing manual manipulation. – avgvstvs Apr 25 '11 at 01:12

Java Regex won't match, any explanations?

4 Answers4