没有匹配在简单的regex发现

Question

Given a token in the format "word_suffix", I want to match and capture the "suffix" part.

For instance, in "Peter_NNP" I want to capture "NNP". I wrote:

        String p="Peter_NNP";
        Matcher matcher=Pattern.compile(".+_(.*\\s)").matcher(p);
        System.out.println(matcher.group(1));

instead of printing "NNP" as I would expect, it arises the following exception:

Exception in thread "main" java.lang.IllegalStateException: No match found
at java.util.regex.Matcher.group(Unknown Source)

Note that "word" and "suffix" part can be made of any character.

Answer 1

You need to call find() to grab your match group. Also, your capture group expects that there should be whitespace at the end of the string, in "Peter_NNP" there is none, .* is enough here.

String s  = "Peter_NNP";
Pattern p = Pattern.compile(".+_(.*)");
Matcher m = p.matcher(s);
if (m.find()) {
  System.out.println(m.group(1)); //=> "NNP"
}

But, I would think a simple split would be fine here:

String s = "Peter_NNP";
String[] parts = s.split("_");
System.out.println(parts[1]);    //=> "NNP"

Answer 2

Just to add on hwnd answer, If you want to capture anything after first underscore(even if there is no character before underscore). Thanks hwnd for making me understand this.

            String s="_NNP";
            Matcher matcher=Pattern.compile(".*?_(.*)").matcher(s);
            while (matcher.find()) {
                System.out.println(matcher.group(1));
              }