detect any combining character in Java

Question

I am looking for a way to detect if a character in a java string "is a combining character" or not. For instance,

String khmerCombiningVowel = 
 new String(new byte[]{(byte) 0xe1,(byte) 0x9f,(byte) 0x80}, "UTF-8"); // unicode 17c0

represents a combining Khmer vowel sign. I have tried "\\p{InCombiningDiacriticalMarks}" regex but it doesn't seem to apply to these particular combining characters. Or even if there is some comprehensive list of all unicode combining character blocks I might be able to make a regex for them?

Here is a link to all Unicode Characters in the Combining Diacritical Marks Block: http://www.fileformat.info/info/unicode/block/combining_diacritical_marks/list.htm — Wiktor Stribiżew, Mar 17 '15 at 22:28
Yeah oddly, this character appears to be a combining mark, but *outside* the "combining diacriticals" block. It's like...some other block maybe? — rogerdpack, Mar 17 '15 at 22:30

score 5 · Accepted Answer · edited May 23 '17 at 11:45

According to Algorithm to check for combining characters in Unicode, there are a number of blocks for combining characters.

Java has a number of helpful functions, try:

String codePointStr = new String(new byte[]{(byte) 0xe1, (byte) 0x9f, (byte) 0x80}, "UTF-8"); // unicode 17c0
System.out.println(codePointStr.matches("\\p{Mc}"));
System.out.println(
    Character.COMBINING_SPACING_MARK == Character.getType(codePointStr.codePointAt(0)));

(prints true in both cases)

In this case, the COMBINING_SPACING_MARK (and related regex \p{gc=Mc}) both refer to the Unicode category "Mark, Spacing Combining" which is basically any character that combines with a previous character while also adding width.

Other regular expressions that may be useful: \p{M} for any kind of mark. If you want to use the Character getType() constants, you can get the same behavior to that by checking if its type is COMBINING_SPACING_MARK or ENCLOSING_MARK, or NON_SPACING_MARK.

ENCLOSING_MARK is a surrounding character, like a circle--also adds width to the character it combines with.

NON_SPACING_MARK includes the Latin alphabet diacritical combining marks, etc. (Marks that basically go on top or below, and don't add any width to the character).

detect any combining character in Java

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