获取匹配字符串的索引与正则表达式

Question

I am trying to fetch the content between the tags. So i made regex for the same.

    final String REGEX_BOLD_END = ".*[<][/][B|b][>].*";
    String input = "<B>Contetnt here</B>";
    Pattern pattern_start = Pattern.compile(".*[<][B|b][>].*");
    Matcher matcher_start = pattern_start.matcher(input);
    Pattern pattern_end = Pattern.compile(REGEX_BOLD_END);
    Matcher matcher_end = pattern_end.matcher(input);
    System.out.println("Tag open");
    if (matcher_start.matches()) {
        System.out.println("At:" + matcher_start.start() + "\tTo:" + matcher_start.end());
        System.out.println(matcher_start.group(0));
    } else {
        System.out.println("Not matched");
    }
    System.out.println("Tag Close");
    if (matcher_end.matches()) {
        System.out.print("At:" + matcher_end.start() + "\tTo:" + matcher_end.end());
    } else {
        System.out.println("Not matched");
    }

My aim is to get the Content here . So i was thinking to get the start and end index and then fetch the substring out of the original input. But i am getting something what i was not expecting.

output:

Tag open

At:0    To:20
<B>Contetnt here</B>
Tag Close
At:0    To:20

Please point out where i am making mistake.

Answer 1

If you're thinking of using substring in relation to Regex'es, you're doing it wrong. The whole point of regular expressions is to not bother with indexes or substring.

Try this instead:

Pattern p = Pattern.compile("<[b|B]>(.*)</[b|B]>");
Matcher m = p.matcher(textToMatch);
if (m.find()) {
    String firstMatch = m.group(1);
}

Edit : Complete, compiling command line program, which outputs "Yay!" when input is "<b>yay!</b>" as per requirement.

import java.util.regex.*;
class Test {
    public static void main(String[] args) {
        Pattern p = Pattern.compile("<[b|B]>(.*)</[b|B]>");
        Matcher m = p.matcher(args[0]);
        if (m.find()) {
            System.out.println(m.group(1));
        }
        else System.out.println("No match");
    }
}