Question

I’m trying to craft a Java regular expression to split strings of the general format “foo – bar” into “foo” and “bar” using Pattern.split(). The “-” character may be one of several dashes: the ASCII ‘-‘, the em-dash, the en-dash, etc. I’ve constructed the following regular expression:

private static final Pattern titleSegmentSeparator = Pattern.compile("\\s(\\x45|\\u8211|\\u8212|\\u8213|\\u8214)\\s");

which, if I’m reading the Pattern documentation correctly, should capture any of the unicode dashes or the ascii dash, when surrounded on both sides by whitespace. I’m using the pattern as follows:

String[] sectionSegments = titleSegmentSeparator.split(sectionTitle);

No joy. For the sample input below, the dash is not detected, and
titleSegmentSeparator.matcher(sectionTitle).find() returns false!

In order to make sure I wasn’t missing any unusual character entities, I used System.out to print some debug information. The output is as follows — each character is followed by the output of (int)char, which should be its’ unicode code point, no?

Sample input:

Study Summary (1 of 10) – Competition

S(83)t(116)u(117)d(100)y(121)
(32)S(83)u(117)m(109)m(109)a(97)r(114)y(121)
(32)((40)1(49) (32)o(111)f(102)
(32)1(49)0(48))(41) (32)–(8211)
(32)C(67)o(111)m(109)p(112)e(101)t(116)i(105)t(116)i(105)o(111)n(110)

It looks to me like that dash is codepoint 8211, which should be matched by the regex, but it isn’t! What’s going on here?

Answer 1

You’re mixing decimal (8211) and hexadecimal (0x8211).

\x and \u both expect a hexadecimal number, therefore you’d need to use \u2014 to match the em-dash, not \u8211 (and \x2D for the normal hyphen etc.).

But why not simply use the Unicode property “Dash punctuation”?

As a Java string: "\\s\\p{Pd}\\s"