Carets (^) in regular expressions

[Alan]

The Java SE 6.0 API documentation for the Pattern class in
java.util.regex says the caret ("^") can be used in a regular
expression to find the beginning of a line. However, it can also be
used to denote negation (see "Character classes" section). How does
Java tell the difference in this usage?

Thanks, Alan

 

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

The Java SE 6.0 API documentation for the Pattern class in
java.util.regex says the caret ("^") can be used in a regular
expression to find the beginning of a line. However, it can also be
used to denote negation (see "Character classes" section). How does
Java tell the difference in this usage?

Java regex does what other regex does: ^ outside [] is start and
^ inside [] is negation.

Arne

 

[Alan]

Arne,
Thanks. This is the first regexp I`ve used. It turns out my
problem was using "^\p" instead of the correct "\P".

Alan

 

[Roedy Green]

Thanks. This is the first regexp I`ve used. It turns out my
problem was using "^\p" instead of the correct "\P".

for other regex hints, see http://mindprod.com/jgloss/regex.html

 

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

Thanks. This is the first regexp I`ve used. It turns out my
problem was using "^\p" instead of the correct "\P".

You could also have used ^ just inside [].

Try running:

import java.util.regex.Pattern;

public class R {
public static void main(String[] args) {
System.out.println(Pattern.matches("\\p{Digit}+", "123"));
System.out.println(Pattern.matches("\\p{Digit}+", "ABC"));
System.out.println(Pattern.matches("\\P{Digit}+", "123"));
System.out.println(Pattern.matches("\\P{Digit}+", "ABC"));
System.out.println(Pattern.matches("[^\\p{Digit}]+", "123"));
System.out.println(Pattern.matches("[^\\p{Digit}]+", "ABC"));
}
}

Arne