Given the history of regular expression implementations, it would be very surprising if Java actually did handle this correctly. Until Perl implemented a solution, the best approach that I'd heard of anyone using for this problem was to first do a DFA match to see if it matched at all, then an NFA match to figure out what the match was.
I don't have a Java compiler handy. But, for instance, this was not handled in Perl 5.005_03, and as of the last time that I checked, was not handled in Ruby, pcre (which is widely used in other applications), or pp-ccre.
If someone wishes to run a test Java program to see whether it has this optimization, I'd be interested to know the result.
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