Regular expression in Java aren't different from regexps in other languages. They use the Perl syntax for the most part. Or are you looking an introduction to regexps in general? Then http://www.regular-expressions.info/ is for you.
Examples of using the java.util.regex package can be found here.
Do you pee on your compost? Does this tiny ad?
a bit of art, as a gift, the permaculture playing cards