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Java Forum / General / June 2007regex
Hi, in this regex I have two different results but why? Pattern p = Pattern.compile("[a-z&&[def]]"); Matcher m = p.matcher("adef"); boolean b = m.find(); // true boolean b2 = Pattern.matches("[a-z&&[def]]", "adef"); // false If I try to use another regex tool as RegexBuddy I also have false But the is the intersection a regex standard feature? Thanks > Hi, in this regex I have two different results but why? > [quoted text clipped - 9 lines] > > Thanks Mind the difference between /find/ and /match/. df. >> Hi, in this regex I have two different results but why? >> [quoted text clipped - 13 lines] > > df. Additionally, if you wonder why your second result is "false" (instead of wondering why the first one is "true"), you might want to learn about quantifiers. Lots of stuff about regexes online, for instance: http://www.regular-expressions.info/ df. > >> Hi, in this regex I have two different results but why? > [quoted text clipped - 20 lines] > > df. the pattern [a-z&&[def]] should mean: a char between 'a' and 'z' AND a char 'd' or 'e' or 'f'. But the test fails! Now my question: are the nested squares and logical && regex standard? If I put in RegexBuddy that pattern [a-z&&[def]] the last square is treated as a single char! >>>> Hi, in this regex I have two different results but why? >>>> Pattern p = Pattern.compile("[a-z&&[def]]"); [quoted text clipped - 15 lines] > the pattern [a-z&&[def]] should mean: > a char between 'a' and 'z' AND a char 'd' or 'e' or 'f'. As a matter of fact, it means "'d', 'e' or 'f'". Sorry, I didn't took notice of the intersection at first, as I focussed on the absence of any quantifier. My second comment was therefore wrong; the results you get are perfectly what one should expect. Again: mind the difference between /find/ and /match/. You regex can capture but one character. So it won't /match/ a four-character-long string. You will however be able to /find/ the pattern in the input. > But the test > fails! Tell us what you'd expect and why. > Now my question: are the nested squares and logical && regex standard? > If I I don't quite remember whether they're part of the POSIX standard but they definitely are supported in the java.util.regex package. > put in RegexBuddy that pattern [a-z&&[def]] the last square is treated > as a single char! Don't know 'bout that. > > Hi, in this regex I have two different results but why? > [quoted text clipped - 13 lines] > > df. Ok I read carefully and I understand that matches() find a complete sequence while find() a sub-sequence. But: boolean b2 = Pattern.matches("[a-z&&[def]]", "ad"); give me false! May be it does not mean find: a char between 'a' and 'z' AND a char 'd' or 'e' or 'f' ???' where is my conceptual error??? > But: > boolean b2 = Pattern.matches("[a-z&&[def]]", "ad"); > > give me false! May be it does not mean find: a char between 'a' and 'z' > AND a char 'd' or 'e' or 'f' ???' where is my conceptual error??? From the Javadocs for Pattern: [a-z&&[def]] d, e, or f (intersection) What you're trying to say is the regex [a-z][def]. For more information, go see http://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.html. There's a lot of information on regex there, and even more if you search for Perl regex. > > But: > > boolean b2 = Pattern.matches("[a-z&&[def]]", "ad"); [quoted text clipped - 10 lines] > There's a lot of information on regex there, and even more if you search > for Perl regex. Does have this intersection the same meaning of the mathematic set intersection concept? If yes this code is also false: boolean b2 = Pattern.matches("[a-z&&[def]]", "de"); // false but d of first a-z and d of def are intersected or NOT! Please give me an example that returns true! > Does have this intersection the same meaning of the mathematic set > intersection concept? [quoted text clipped - 3 lines] > > Please give me an example that returns true! The regular expression means the intersection between "any one from a to z" and "d, e or f"... which is "d, e, or f". And then you match a string to that result. If you look carefully, the regular expression has only one single class with no quantifiers. So it will never match "de", which has two characters. On Wed, 20 Jun 2007 13:42:05 GMT, Joshua Cranmer <Pidgeot18@verizon.net> wrote, quoted or indirectly quoted someone who said : >[a-z&&[def]] d, e, or f (intersection) the way would normally use && intersection is like this: [a-z]&&[^m-p]] a-z but not m-p -- Roedy Green Canadian Mind Products The Java Glossary http://mindprod.com > But: > boolean b2 = Pattern.matches("[a-z&&[def]]", "ad"); > > give me false! May be it does not mean find: > a char between 'a' and 'z' AND a char 'd' or 'e' or 'f' ???' > where is my conceptual error??? Let's take it apart. [a-z&&[def]] The inner class, [def] means either d, e, or f will match. The first part of the outer class, a-z means a to z will match. Combining first part with second part with &&, which means INTERSECTION. The Java API doc of the Pattern class gave you exactly the above example: [a-z&&[def]] d, e, or f (intersection) What you're looking for is probably [a-z][def]. >boolean b2 = Pattern.matches("[a-z&&[def]]", "ad"); > >give me false! May be it does not mean find: >a char between 'a' and 'z' AND a char 'd' or 'e' or 'f' ???' >where is my conceptual error??? What SINGLE character is between a - z and also in the list d e f? There are only three possibilities that fit the bill d e and f "and" does not mean "and is followed by" it means "and also is" -- Roedy Green Canadian Mind Products The Java Glossary http://mindprod.com >Pattern p = Pattern.compile("[a-z&&[def]]"); >Matcher m = p.matcher("adef"); [quoted text clipped - 5 lines] > >But the is the intersection a regex standard feature? Here is your code in runnable form: import java.util.regex.Matcher; import java.util.regex.Pattern; public class Intersection { /** * test harness * * @param args not used */ public static void main ( String[] args ) { Pattern p = Pattern.compile("[a-z&&[def]]"); Matcher m = p.matcher("adef"); boolean b = m.find(); // true System.out.println(b); boolean b2 = Pattern.matches("[a-z&&[def]]", "adef"); // false System.out.println(b2); } } find is true because the letter d exists in the string adef. The pattern searches for any of "def'. matches is false because 'adef' does not match the pattern. Patterns must be a single character long and be a def. See http://mindprod.com/jgloss/regex.html#MATCHINGANDFINDING -- Roedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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