Java regex pattern query

Question

Just a quick question about Java regex patterns! So say if I had a method like..

    public void example()
    {
      Pattern p = Pattern.compile("\\d*");
      Matcher m = p.matcher("ab34ef");
      boolean b = false;
      while (b = m.find()) 
      {
        System.out.println(m.start() + " " + m.group()); 
      }
    }

If I ran this I would end up with the following output..

I understand how this works apart from how it ends up at 6, I thought it would finish on 5 could someone please explain this to me? Thanks!

6 is for the empty character at the end. – Rohit Jain Jan 06 '14 at 17:45 — Rohit Jain, Jan 06 '14 at 17:45
BTW your `b` is entirely redundant. You never read it. – Marko Topolnik Jan 06 '14 at 17:46 — Marko Topolnik, Jan 06 '14 at 17:46

score 3 · Accepted Answer · answered Jan 06 '14 at 17:52

In your string, "ab34ef", there are 7 "empty characters" with a value of "". They are located between each of the normal characters. It attempts to find a match starting on each empty character, not each normal character; i.e. the location of each | in the following: "|a|b|3|4|e|f|".

Java regex pattern query

1 Answers1