Java Regex Fails to Find a match

Question

This should return true, but instead returns false.

"ADC".matches("A.*?C")

I've tested it on a javascript regex tester : http://regexpal.com/

and it works, why doesn't it work in Java?

EDIT: Same with this:

System.out.println("DEAGHHF".matches("(A.*?C|C.*?A|D.*?C|C.*?D|A.*?F|F.*?A)"));

Returns false, regexpal returns true (aswhile as other javascript regex engines).

Sorry, for the little advert (i only use the tool myself, i don't work for them) but you can try the software regexpal mentions "regexbuddy" which allows you to even export a function to use in Java. — Joe Simpson
– Joe Simpson, Commented May 7, 2011 at 19:50
Are you sure that you have shown us the right expression and input? That expression matches that input on regexpal.com for me and when I run "ADC".matches("A.*?C"). — Andrew Hare
– Andrew Hare, Commented May 7, 2011 at 19:54
Why should DEAGHHF match A.?C|C.?A|D.?C|C.?D|A.?F|F.?A The regexp says that the string should be of length 2 or 3. The string that you have is way longer than that, so you can only get a partial match. — Kaj
– Kaj, Commented May 7, 2011 at 20:05

aioobe · Accepted Answer · 2011-05-07 20:07:19Z

6

No, it returns true.

System.out.println("ADC".matches("A.*?C"));

prints true.

The regexpal.com implementation seems to be buggy (which is understandable since it is version 0.1.4). Try entering ABC repeatedly. Only every second ABC gets rejected. (At least when viewing it in my version of firefox.)

Regarding your edit:

A.?C|C.?A|D.?C|C.?D|A.?F|F.?A

is interpreted as

A.*?C   or
C.*?A   or
D.*?C   or
C.*?D   or
A.*?F   or
F.*?A

In other words

Something that starts with A and ends with C, or
Something that starts with C and ends with A, or
Something that starts with D and ends with C, or
....
Something that starts with F and ends with A,

Since "DEAGHHF" starts with D and ends with F, it won't match.

Perhaps you're looking for the Matcher.find method

edited May 7, 2011 at 20:07

answered May 7, 2011 at 19:49

aioobe

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3 Comments

Voo Over a year ago

Yeah works for me too. For testing RegEx for Java I recommend regexplanet.com/simple/index.html - got that from SO myself. Really great implementation with quite some useful bells and whistles (especially the "get regex as java string" is awesome!)

Ajay Over a year ago

Sorry the asteriks didn't show up, fixed first post again. Thanks

Ajay Over a year ago

Matcher was what I was looking for, correct, thank you. And your explanation of the regex was helpful.

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