java - Regular Expressions example -

i’m bit confused example... don’t understand written in string pattern. also, find? learning tutorialspoint.

please, can me understand it?

code:

import java.util.regex.matcher; import java.util.regex.pattern;  public class regexmatches {     public static void main(string args[]) {          // string scanned find pattern.         string line = "this order placed qt3000! ok?";         string pattern = "(.*)(\\d+)(.*)";          // create pattern object         pattern r = pattern.compile(pattern);          // create matcher object.         matcher m = r.matcher(line);         if (m.find()) {             system.out.println("found value: " + m.group(0));             system.out.println("found value: " + m.group(1));             system.out.println("found value: " + m.group(2));         } else {             system.out.println("no match");         }     } } 

output:

found value: order placed qt3000! ok?
found value: order placed qt300
found value: 0

the pattern has 3 capture groups

• (.*) means 0 or more of character (capture group 1)
• (\\d+) means 1 or more digits (capture group 2)
• (.*) means 0 or more of character (capture group 3)

when find() called "attempts find next subsequence of input sequence matches pattern." (matcher.find())

when call these lines:

system.out.println("found value: " + m.group(0)); system.out.println("found value: " + m.group(1)); system.out.println("found value: " + m.group(2)); 

• m.group(0) means entire string regex evaluated
• m.group(1) refers capture group 1 (zero or more of character)
• m.group(2) refers capture group 2 (one or more digits)
• you're not outputting capture group 3 (zero or more of character)

you'll see m.group(1) returned this order placed qt300 , last 0 left behind m.group(2) because capture group 2 must have @ least 1 digit.

if add capture group 3 (m.group(3)) output display remaining string after last 0 of m.group(2).

in other words:

system.out.println("found value: " + m.group(0)); system.out.println("found value: " + m.group(1)); system.out.println("found value: " + m.group(2)); system.out.println("found value: " + m.group(3)); 

would display:

found value: order placed qt3000! ok? found value: order placed qt300 found value: 0 found value: ! ok? 

hope helps!