This post originated from an RSS feed registered with Java Buzz by Matt Quail. Original Post: java.util.regex.Pattern StackOverflowError's on (x|y)* Feed Title: Matt Quail's Java blog Feed URL: http://fisheye.cenqua.com/category/java/feed/ Feed Description: The latest java related logs from Matt Quail's blog at madbean.com Latest Java Buzz Posts Latest Java Buzz Posts by Matt Quail Latest Posts From Matt Quail's Java blog

I've been doing a fair whack of regex processing in Java recently. I must admit that having a regex library in the language is very useful, and Java's java.util.regex.Pattern implements a very complete regex library (all the "Perl5" stuff, non-greedy quantifiers, Unicode character classes, etc).

So I was completely surprised when it started throwing StackOverflowError. The following code highlights the problem (reproduced on Sun's JDK1.5.0-b2 and JDK1.4.2_01). Any pattern like (x|y)* (an alternative wrapped in a star) is implemented recursively by Pattern. Each matched alternative uses about 5 method calls on the stack.