About learning regular expression

Useful regex test site for java:

http://www.ocpsoft.org/tutorials/regular-expressions/java-visual-regex-tester/

http://java-regex-tester.appspot.com/

Very good site(non-java):

http://regexr.com/

Very good learning site:

http://www.regular-expressions.info/

http://www.bearcave.com/software/antlr/antlr_examples.html