Tuesday, October 25, 2011

Java: Regular expression Library

Ok I always forget how to use java regular expressions and get confused so the following is the list of examples that will help my brain out (I will add stuff over time.)


Ends With .java : .*\\.java
Starts With helloDolly: helloDolly.*
Phone number: ^\\(?([0-9]{3})\\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$

. Everthing (any character one only)
^ Not
* Many
\ Escape
[] Grouping
$ End of line
? Makes the preceding item optional.

| (pipe) Causes the regex engine to match either the part on the left side, or the part on the right side. Can be strung together into a series of options.
+ Repeats the previous item once or more.

\d A digit: [0-9]
\D A non-digit: [^0-9]
\s A whitespace character: [ \t\n\x0B\f\r]
\S A non-whitespace character: [^\s]
\w A word character: [a-zA-Z_0-9]
\W A non-word character: [^\w]



 
.* Everything (any character many times)


a* match all sequential a's 
  
Character Classes
[abc] a, b, or c (simple class)
[^abc] Any character except a, b, or c (negation)
[a-zA-Z] a through z, or A through Z, inclusive (range)
[a-d[m-p]] a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]] d, e, or f (intersection)
[a-z&&[^bc]] a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]] a through z, 



SymbolMeaning
* 0 or more times
+ 1 or more times
?0 or 1 time
{n} Exactly n number of times
{n,m} n to m number of times
References:
http://www.omicentral.com/cheatsheets/JavaRegularExpressionsCheatSheet.pdf
http://download.oracle.com/javase/1.4.2/docs/api/java/util/regex/Pattern.html
http://www.regular-expressions.info/reference.html  
http://www.javaworld.com/javaworld/jw-07-2001/jw-0713-regex.html?page=2

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