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From: Gene Wirchenko <genew@ocis.net>
Newsgroups: comp.lang.java.programmer
Subject: Re: Confusion about String.matches method
Date: Wed, 08 Jun 2011 07:50:13 -0700
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On Tue, 07 Jun 2011 21:18:54 -0700, Roedy Green
<see_website@mindprod.com.invalid> wrote:

[snip]

>The problem with regexes is all it takes is one char off an the whole
>thing does not work.  You have no clue where the problem is.  You
>rarely find errors with syntax checking. There is no trace.
>The other problem is a regex will work 90% of the time.  It may be
>quietly rejecting a small percentage of the strings, and you might not
>notice.

     There are more problems than that.

     I assume that you are familiar with this quote:
Some people, when confronted with a problem, think "I know, I'll use
regular expressions."   Now they have two problems.

     I find regexes to be less than totally useful.  I sometimes have
to define a format string with substitution parameters.  Here is an
example:
Per client's instruction, the total of all invoices for the current
month will be charged against the supplied credit card number on %D
unless we hear otherwise prior to that date.

     The date gets substituted for the %D.  There are a few rules.
There must be one and only "%D" string.  "%" is an escape character
and is doubled for the literal "%".

     I could write a regex for this, BUT I also have to have a routine
for executing the string substitution, and regexes do not help with
this.  I do not want two rather different versions of the code.  (As
it is, I have two versions of code that are somewhat similar.)  More
importantly, if one routine gets changed, so should the other, and it
should be obvious how to do it.

     If I wanted to add a second variable to the example above, say a
contact name, and wanted the constraint of appearing once and only
once, using a regex would get even uglier.

     I could use regexes for such things as validating with no
interpretation, but such data that I have to validate usually has
trivial formatting.  For example, a Canadian Postal Code is "A9A 9A9"
with some limitations on the alphabetic characters.  A regex would be
overkill.

Sincerely,

Gene Wirchenko