RegEx

[Venkat Sidh]

Have a question about RegEx. The following question is from Examulator mock-up,

   import java.util.regex.*;
public class Music{
    String s = " rap rapture wrap" ;
    public static void main(String argv[]){
new Music();
   }
    Music(){
String regex = "r\\wp?";
Pattern pattern = Pattern.compile(regex);
Matcher matcher =pattern.matcher(s);
while(matcher.find()){
    System.out.print(matcher.group());
}    
    }
}
 
 

I do not understand how o/p is obtained as rapraprerap. Can anybody shed some light on this. Thanks.

[Henry Wong]

Originally posted by Venkat Sidh:
Have a question about RegEx. The following question is from Examulator mock-up,

  String regex = "r\\wp?"; 

I do not understand how o/p is obtained as rapraprerap. Can anybody shed some light on this. Thanks.

The regular expression pattern is a letter "r", followed by a required word character, followed by an optional letter "p". The pattern will match 4 times...

"rap" from the first word

"rap" from the beginning of the second word "rapture"

"re" from the end of second word

"rap" from the end of the third word "wrap"

Henry

[Venkat Sidh]

Henry,

Thanks for explanatory answer.

The regular expression pattern is a letter "r", followed by a required word character, followed by an optional letter "p". The pattern will match 4 times...

Actually I'm confused about ? in expression, does ? (greedy quantifier) denote zero or one instance of character p?

[marc weber]

Originally posted by Venkat Sidh:
...Actually I'm confused about ? in expression, does ? (greedy quantifier) denote zero or one instance of character p?

Yes, this is why it's matching "re" from the end of the second word.

r matches r

\\w matches the "word character" e

p? matches zero occurrences of p

So the match here is just re.