Java Pattern / Matcher not finding word break

Question

I am having trouble with Java Pattern and Matcher. I've included a very simplified example of what I'm trying to do.

I had expected the pattern ".\b" to find the last character of the first word (or "4" in the example), but as I step through the code, m.find() always returns false. What am I missing here?

Why does the following Java code always print out "Not Found"?

                Pattern p = Pattern.compile(".\b");
                Matcher m = p.matcher("102939384 is a word");
                int ixEndWord = 0;
                if (m.find()) {
                    ixEndWord = m.end();
                    System.out.println("Found: " + ixEndWord);
                } else {
                    System.out.println("Not Found");
                }

You need to escape special characters in the regex: `".\\b"` — AntonH, Oct 08 '14 at 20:40
I've put it as an answer, with somewhat of an explaination. You can accept that as the answer :) — AntonH, Oct 08 '14 at 20:48

score 3 · Accepted Answer · answered Oct 08 '14 at 20:47

3

You need to escape special characters in the regex: ".\\b"

Basically, in a String the backslash has to be escaped. So "\\" becomes the character '\'.

So the String ".\\b" becomes the litteral String ".\b", which will be used by the Pattern.

answered Oct 08 '14 at 20:47

AntonH

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score 0 · Answer 2 · answered Oct 08 '14 at 20:48

0

To expand upton AntonH's comment, whenever you want the "\" character to appear in a regex expression, you have to escape it so that it first appears in the string you are passing in.

As is, ".\b" is the string of a dot . followed by the special backspace character represented by \b, compared to ".\\b", which is the regex .\b.

answered Oct 08 '14 at 20:48

Mshnik

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Hang on, is it a dot, or the regex dot representing any character? – Jeremy Goodell Oct 08 '14 at 20:49
1

just a dot will match any character, as expected: http://stackoverflow.com/questions/1480284/java-regular-expression-value-split-the-back-slash-dot-divides-by-char – Mshnik Oct 08 '14 at 20:50

Java Pattern / Matcher not finding word break

2 Answers2