May 2nd, 2014 by Lincoln Baxter III

How to interrupt a long-running “infinite” Java regular expression

If you’ve ever done a lot of work with Regular Expressions, you’re probably familiar with the concept of catastrophic backtracking, which means that the engine is forced to calculate permutations of exponential proportions. For instance, click here run this example and see how long it takes (should be about 5-10 seconds to time out):
public class LongRunningRegexExample
   public static void main(String[] args) throws InterruptedException
      final Pattern pattern = Pattern.compile("(0*)*A");
      final String input = "00000000000000000000000000";

      long startTime = System.currentTimeMillis();
      Matcher matcher = pattern.matcher(input);
      matcher.find(); // runs for a long time!
      System.out.println("Regex took:" + (System.currentTimeMillis() - startTime) + "ms");
However, a small change results in near instantaneous response. Why?
July 4th, 2013 by Lincoln Baxter III

An even better visual regular expression tester

For those of you who have not seen the Visual Regex Tester yet, this video should be informative, and for those of you who have, make sure to check out the new reverse-syntax highlighting features that I’ve recently added. My goal is to make this tester as useful and fun as possible; it should be a regular stable of regular expression development.