Though regex support in Java was introduced several years ago (but not that many: JDK 1.4 AFAIK, 2002 circa, if we mean the java.util.regex package), it still doesn't offer advanced things such as match-time code evaluation, match-time pattern interpolation and conditional interpolation.

So, for example, with a Java regex you can't build a recursive pattern (to check for instance if the parentheses in a text are balanced), while in Perl you can ;-)

Update

It can also be interesting to see how more verbose Java regexes are compared to Perl regexes.
Here is a simple Perl example:

my $pat = qr/a+b/;
my $res = "aaab" =~ $pat;
[download]

and here is its Java counterpart:

import java.util.regex.*;
Pattern pat = Pattern.compile("a+b");
Matcher mat = pat.matcher("aaab");
boolean res = mat.matches();
[download]

Really, the above 2 last lines could be substituted by the following somewhat shorter code:

boolean res = pat.matcher("aaab").matches();
[download]

but if you don't explicitly instantiate a Matcher object, you can't have several things such as match, prematch, postmatch etc. which Perl gives you for free (through the various predefined variables $&, $`, $' etc.)

Ciao, Emanuele.