SCJP 6 K&B book page no: 499

[Madi Meka]

 
import java.util.regex.*

class Regex {
  public static void main(String [] args){
   Pattern p = Patter.compile(args[0]);
   Matcher m = p.matcher(args[1]);
   System.out.println("pattern is  "+m.pattern());
   while(m.find()){
       System.out.println(m.start() + " " + m.group());    
             
      

% java Regex "\d\w" "ab4 56_7ab"


Produces output:

patter is \d\w
4 56
7 7a



Can anyone explain how can i get that output?? \d\w. What i understood is it should search for a digit follwed by a char. but how is that output coming?

Please help.

Thanks,
Madhavee Latha

[Siva Masilamani]

Well the first part of output in the first line is the start index of the pattern.As you know the index starts from 0 so it starts its searches from 0 and the first digit it encounters is 5 and then it should be followed by word character which could be [a-zA-Z0-9_] so 56 is the first pattern that matches adn the index of 5 is 4 hence the output is 4 starting position and the matched string 56.

4 inthe output is not the 4 from the input String.

Hope it helps

[Madi Meka]

Ya i understand that 4 and 7 are the indexes. but couldn't frame 56 as i thought it should result in 56_7ab for \d\w(digit followed by a string).

[Atwal Usha]

Can anyone explain how can i get that output?? \d\w. What i understood is it should search for a digit follwed by a char. but how is that output coming?

You get \d\w in the output because you have instructed the code to do so. Please see Line 1 here you are displaying the regex pattern being used.

class Regex3 {  
   public static void main(String [] args){  
    Pattern p = Pattern.compile(args[0]);  
    Matcher m = p.matcher(args[1]);  
    System.out.println("pattern is  "+m.pattern());  //Line 1
    while(m.find()){  
        System.out.println(m.start() + " " + m.group()); 
    } }
}    

[Siva Masilamani]

/d/w means one digit followed by one letter

/w means a word character not a word.Word character could be a-zA-Z0-9 or_

So as per your input string the first number is 4 but it should be followed by word character but space is not word character and hence no match and regex move on to fins next number here it finds 5 then it finds 6 followed by it .since 6 is word character followed bu digit 5 it matches the pattern and hence the output and continues.......

[Madi Meka]

ohh okk... Thanks a lot.