Regular expression match a sentence [closed]

Question

How can I match a sentence of the form "Hello world" or "Hello World". The sentence may contain "- / digit 0-9". Any information will be very helpful to me. Thank you.

Answer 1

This one will do a pretty good job. My definition of a sentence: A sentence begins with a non-whitespace and ends with a period, exclamation point or a question mark (or end of string). There may be a closing quote following the ending punctuation.

[^.!?\s][^.!?]*(?:[.!?](?!['"]?\s|$)[^.!?]*)*[.!?]?['"]?(?=\s|$)

import java.util.regex.*;
public class TEST {
    public static void main(String[] args) {
        String subjectString = 
        "This is a sentence. " +
        "So is \"this\"! And is \"this?\" " +
        "This is 'stackoverflow.com!' " +
        "Hello World";
        String[] sentences = null;
        Pattern re = Pattern.compile(
            "# Match a sentence ending in punctuation or EOS.\n" +
            "[^.!?\\s]    # First char is non-punct, non-ws\n" +
            "[^.!?]*      # Greedily consume up to punctuation.\n" +
            "(?:          # Group for unrolling the loop.\n" +
            "  [.!?]      # (special) inner punctuation ok if\n" +
            "  (?!['\"]?\\s|$)  # not followed by ws or EOS.\n" +
            "  [^.!?]*    # Greedily consume up to punctuation.\n" +
            ")*           # Zero or more (special normal*)\n" +
            "[.!?]?       # Optional ending punctuation.\n" +
            "['\"]?       # Optional closing quote.\n" +
            "(?=\\s|$)", 
            Pattern.MULTILINE | Pattern.COMMENTS);
        Matcher reMatcher = re.matcher(subjectString);
        while (reMatcher.find()) {
            System.out.println(reMatcher.group());
        } 
    }
}

Here is the output:

This is a sentence.
So is "this"!
And is "this?"
This is 'stackoverflow.com!'
Hello World

Matching all of these correctly (with the last sentence having no ending punctuation), turns out to be not so easy as it seems!