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From: Jim Janney <jjanney@shell.xmission.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Keeping the split token in a Java regular expression
Date: Tue, 27 Mar 2012 08:15:02 -0600
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laredotornado <laredotornado@zipmail.com> writes:

> Hi,
>
> I'm using Java 6.  I want to split a Java string on a regular
> expression, but I would like to keep part of the string used to split
> in the results.  What I have are Strings like
>
>     Fri 7:30 PM, Sat 2 PM, Sun 2:30 PM
>
> What I would like to do is split the expression wherever I have an
> expression matching /(am|pm),?/i .  Hopefully I got that right.  In
> the above example, I would like the results to be
>
>     Fri 7:30 PM
>     Sat 2 PM
>     Sun 2:30 PM
>
> But with String.split, the split token is not kept within the
> results.  How would I write a Java parsing expression to do what I
> want?
>
> Thanks, - Dave

You want to match ,? only when it is preceded by (am|pm).  That's what
lookbehind is for:

public class LookBehind {
  public static void main(String[] args) {
    
    String data = "Fri 7:30 PM, Sat 2 PM, Sun 2:30 PM";
    String pattern = "(?i)(?<=am|pm),?";
    
    String[] split = data.split(pattern);
    for (String s : split) {
      System.out.println("'" + s + "'");
    }
  }
}

See http://www.regular-expressions.info/lookaround.html for a tutorial.

-- 
Jim Janney