FULL PRODUCT VERSION :
java version "1.5.0_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_05-b05)
Java HotSpot(TM) Client VM (build 1.5.0_05-b05, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP - Home Edition - Version 2002 - Service Pack 2

A DESCRIPTION OF THE PROBLEM :
The API documentation for the class java.util.regex.Pattern states that "Groups beginning with (? are pure, non-capturing groups" which I believe is false and should be "(?:" instead of "(?".

I got the following error when trying to use "(?" instead of a "(":
java.util.regex.PatternSyntaxException: Unknown inline modifier near index 144

I looked up the documentation for Perl, and there it stated that non-capturing groups should begin with "(?:". Since there is alot of analogy between regular expressions in Java and Perl, I tried to use "(?:" and it worked perfectly.

So, in conclusion, or (a) the documentation is incorrect, or (b) the implementation is incorrect.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Using Java version 1.5.0_05, create a simple class as follows:

import java.util.regex.*;
public class Main {
    public static void main(String[] args) {
        System.out.println(Pattern.matches("(a).*", "abc"));
        System.out.println(Pattern.matches("(?:a).*", "abc"));
        System.out.println(Pattern.matches("(?a).*", "abc"));
    }
}

Execute the main method of this class.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expected to see the second statement return false (because there is no semicolon present in the string "abc").

ACTUAL -
The first two print statements worked ok, but the third one throws a java.util.regex.PatternSyntaxException exception.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.util.regex.PatternSyntaxException: Unknown inline modifier near index 2
(?a).*
at java.util.regex.Pattern.error(Pattern.java:1650)
at java.util.regex.Pattern.group0(Pattern.java:2446)
at java.util.regex.Pattern.sequence(Pattern.java:1715)
at java.util.regex.Pattern.expr(Pattern.java:1687)
at java.util.regex.Pattern.compile(Pattern.java:1397)
at java.util.regex.Pattern.<init>(Pattern.java:1124)
at java.util.regex.Pattern.compile(Pattern.java:817)
at java.util.regex.Pattern.matches(Pattern.java:919)
at whatif.Main.main(Main.java:32)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.regex.*;
public class Main {
    public static void main(String[] args) {
        System.out.println(Pattern.matches("(a).*", "abc"));
        System.out.println(Pattern.matches("(?:a).*", "abc"));
        System.out.println(Pattern.matches("(?a).*", "abc"));
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use "(?:" instead of the documented "(?" for non-capturing groups.