Regex Doubt

[Prateek Rawal]

import java.util.regex.Matcher;  
import java.util.regex.Pattern;  
  
public class Regex   
{  
    public static void main(String [] args)  
    {  
        String strpattern = "\\d*?";  
        Pattern p = Pattern.compile(strpattern);  
        Matcher m = p.matcher("abc4jk");  
        while(m.find())  
        {  
            System.out.println(m.start()+m.group());      
        }  
    }  
}

The above code does not matches any numbers, why so ?

"\\d*?" definitely means zero or more digits reluctantly, then why doesn't it matches 4 in the source string?

However if i change the pattern to "(\\d*)?" it matches, i can't understand why?

PS: i know this has been posted earlier, but in that post, no fruitful conclusion was drawn as to why is this happening?

[Deepak Bala]

Reluctant quantifiers are different from greedy quantifiers -> http://www.devarticles.com/c/a/Java/Advanced-Regex/3/

Also, take a look at the Pattern class javadoc. It lists the reluctant / greedy quantifiers

[Prateek Rawal]

I have another problem arising:

  import java.util.regex.*;
class Now {

public static void main(String[] args){

Pattern p = Pattern.compile(args[0]);
Matcher m = p.matcher(args[1]);
System.out.println(m.pattern()+"yers");
while(m.find()){
System.out.println(m.start() + " " + m.end() + " " + m.group());
}


}
}  

When i write java Now a* ababaaaab,
i get the following output
aarzoo1<songs.pk>.mp3yers

Let alone me matching, it is reading the pattern as one of the songs on my desktop(this code file is also on desktop), but when i write
java Now b* ababaaaab
i get the desired output along with desired matching........

Why is this weird thing happening?

[Ireneusz Kordal]

Use double quotes when passing arguments from the command line and you will get desired output
java Now "a*" ababaaaab
instead of
java Now a* ababaaaab

java command treats * and ? characters in the same way as dir or ls commands in unix or dos.
Try to run this program from the command line with * argument and you will see that it will print list of files in your current working directory:

    public static void main(String[] args) {

        for( String s : args){
            System.out.format("%s\n", s);
        }
    }

But if you invoke it with "*" argument, it will simply print *.

[Prateek Rawal]

Thanks!!!

But when i write java Now (b*) "abbabaaabbb", it works, why?

Is '(' valid instead of " ?

But it doesn't work with java <b*> "abbaaaabb", why so?