regex question from K & B

[sridhar row]

import java.util.regex.*;
class Regex {
public static void main(String [] args) {
Pattern p = Pattern.compile(args[0]);
Matcher m = p.matcher(args[1]);
boolean b = false;
System.out.println("Pattern is " + m.pattern());
while(b = m.find()) {
System.out.println(m.start() + " " + m.group());
}
}
}
********************************************
% java Regex "\d\w" "ab4 56_7ab"
Produces the output
Pattern is \d\w
4 56
7 7a
*********************************************
% java Regex "\w\d" "ab4 56_7ab"
Produces the output
Pattern is \w\d
1 b4
4 56
6 _7

In the above the 2 outputs are quite different. Can somebody explain the outputs wrt the combination if \d\w and \w\d..i understand the difference between \d and \w but dont get it when used in combination. Thanks!
[ January 17, 2008: Message edited by: sridhar row ]

[Pranav Bhatt]

/d=> digit
/w=> letter,digit or underscore(_)

/d/w searchs for 1st char that is digit and next is either letter,digit or underscore(_). So you got the collowing-:

% java Regex "\d\w" "ab4 56_7ab"
Produces the output
Pattern is \d\w
4 56
7 7a

/w/d searches for 1st char as letter,digit or underscore(_) and the next one should be digit. Here you got the following-:

% java Regex "\w\d" "ab4 56_7ab"
Produces the output
Pattern is \w\d
1 b4
4 56
6 _7

hope this clears

[sridhar row]

i guess i do..thanks
[ January 17, 2008: Message edited by: sridhar row ]