Java RegEx Matcher.groupCount returns 0

问题

I know this has been asked but I am unable to fix it

For a book object with body (spanish): "quiero mas dinero" (actually quite a bit longer)

My Matcher keeps returning 0 for:

    String s="mas"; // this is for testing, comes from a List<String>
    int hit=0;
    Pattern p=Pattern.compile(s,Pattern.CASE_INSENSITIVE);
    Matcher m = p.matcher(mybooks.get(i).getBody());
    m.find();
    System.out.println(s+"  "+m.groupCount()+"  " +mybooks.get(i).getBody());
    hit+=m.groupCount();

I keep getting "mas 0 quiero mas dinero" on console. Why oh why?

回答1:

From the javadoc of Matcher.groupCount():

Returns the number of capturing groups in this matcher's pattern.
Group zero denotes the entire pattern by convention. It is not included in this count.

If you check the return value from m.find() it returns true, and m.group() returns mas, so the matcher does find a match.

If what you are trying to do is to count the number of occurances of s in mybooks.get(i).getBody(), you can do it like this:

String s="mas"; // this is for testing, comes from a List<String>
int hit=0;
Pattern p=Pattern.compile(s,Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(mybooks.get(i).getBody());
while (m.find()) {
    hit++;
}

回答2:

How could I then find the number of "mas" (or any other) words in a string without looping?

You could use StringUtils in Apache Commons:

int countMatches = StringUtils.countMatches("quiero mas dinero...", "mas");

回答3:

You can add parenthesis in the regExp, then it is "(mas)" in your example.

回答4:

You can add parenthesis in the regExp, then it is "(mas)" in your example.

That way is not suitable for this task. It shows number of capturing groups contain result of Matcher m. In this case even if pattern is "(mas)" for input text like "mas mas" m.groupcount() show 1 - one and only groop for both matches.

So first response is correct and the only possible for the purpose of matches counting.

来源：https://stackoverflow.com/questions/12413974/java-regex-matcher-groupcount-returns-0

标签

java

regex

matcher