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    <p>Next time you need a regex explained, you can use the following <a href="http://rick.measham.id.au/paste/explain.pl" rel="noreferrer"><code>explain.pl</code></a> service from Rick Measham:</p> <pre><code>Regex: [^,]*|.+(,).+ NODE EXPLANATION -------------------------------------------------------------------------------- [^,]* any character except: ',' (0 or more times (matching the most amount possible)) -------------------------------------------------------------------------------- | OR -------------------------------------------------------------------------------- .+ any character except \n (1 or more times (matching the most amount possible)) -------------------------------------------------------------------------------- ( group and capture to \1: -------------------------------------------------------------------------------- , ',' -------------------------------------------------------------------------------- ) end of \1 -------------------------------------------------------------------------------- .+ any character except \n (1 or more times (matching the most amount possible)) </code></pre> <hr> <pre><code>Regex: (\()?\d+(?(1)\)) NODE EXPLANATION -------------------------------------------------------------------------------- ( group and capture to \1 (optional (matching the most amount possible)): -------------------------------------------------------------------------------- \( '(' -------------------------------------------------------------------------------- )? end of \1 (NOTE: because you're using a quantifier on this capture, only the LAST repetition of the captured pattern will be stored in \1) -------------------------------------------------------------------------------- \d+ digits (0-9) (1 or more times (matching the most amount possible)) -------------------------------------------------------------------------------- (?(1) if back-reference \1 matched, then: -------------------------------------------------------------------------------- \) ')' -------------------------------------------------------------------------------- | else: -------------------------------------------------------------------------------- succeed -------------------------------------------------------------------------------- ) end of conditional on \1 </code></pre> <h3>Links</h3> <ul> <li><a href="http://rick.measham.id.au/paste/explain.pl" rel="noreferrer">http://rick.measham.id.au/paste/explain.pl</a></li> </ul> <hr> <h3>Note on conditionals</h3> <p>JAVA DOES NOT SUPPORT CONDITIONALS! An unconditionalized regex for the second pattern would be something like:</p> <pre><code>\d+|\(\d+\) </code></pre> <p>i.e. a non-zero repetition of digits, with or without surrounding parentheses.</p> <h3>Links</h3> <ul> <li><a href="http://www.regular-expressions.info/conditional.html" rel="noreferrer">regular-expressions.info/If-then-else conditionals</a> <blockquote> <p>Conditionals are supported by the JGsoft engine, Perl, PCRE and the .NET framework.</p> </blockquote></li> </ul> <hr> <h3>The patterns in depth</h3> <p>Here's a test harness for the first pattern</p> <pre><code> import java.util.regex.*; //... Pattern p = Pattern.compile("[^,]*|.+(,).+"); String[] tests = { "", // [] is a match with no commas "abc", // [abc] is a match with no commas ",abc", // [,abc] is not a match "abc,", // [abc,] is not a match "ab,c", // [ab,c] is a match with separating comma "ab,c,", // [ab,c,] is a match with separating comma ",", // [,] is not a match ",,", // [,,] is not a match ",,,", // [,,,] is a match with separating comma }; for (String test : tests) { Matcher m = p.matcher(test); System.out.format("[%s] is %s %n", test, !m.matches() ? "not a match" : m.group(1) != null ? "a match with separating comma" : "a match with no commas" ); } </code></pre> <h3>Conclusion</h3> <ul> <li>To match, the string must fall into one of these two cases: <ul> <li>Contains no comma (potentially an empty string)</li> <li>Contains a comma that separates two non-empty strings</li> </ul></li> <li>On a match, <code>\1</code> can be used to distinguish between the two cases</li> </ul> <p>And here's a similar test harness for the second pattern, rewritten without using conditionals (which isn't supported by Java):</p> <pre><code> Pattern p = Pattern.compile("\\d+|(\\()\\d+\\)"); String[] tests = { "", // [] is not a match "0", // [0] is a match without parenthesis "(0)", // [(0)] is a match with surrounding parenthesis "007", // [007] is a match without parenthesis "(007)", // [(007)] is a match with surrounding parenthesis "(007", // [(007] is not a match "007)", // [007)] is not a match "-1", // [-1] is not a match }; for (String test : tests) { Matcher m = p.matcher(test); System.out.format("[%s] is %s %n", test, !m.matches() ? "not a match" : m.group(1) != null ? "a match with surrounding parenthesis" : "a match without parenthesis" ); } </code></pre> <p>As previously said, this matches a non-zero number of digits, possibly surrounded by parenthesis (and <code>\1</code> distinguishes between the two).</p>
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    1. COwow didn't know about that site. Looks great. How 'complex' can the program handle?
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    2. CO@ggfan: it's just mechanical translation. It's probably not that hard to cover all syntax. To machine, regex isn't all that "confusing".
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    3. CO+1, learnt something new.
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