How can I iterate through the unicode codepoints of a Java String?

java, string, unicode

Solution

Yes, Java uses a UTF-16-esque encoding for internal representations of Strings, and, yes, it encodes characters outside the Basic Multilingual Plane (BMP) using the surrogacy scheme.

If you know you'll be dealing with characters outside the BMP, then here is the canonical way to iterate over the characters of a Java String:

final int length = s.length();
for (int offset = 0; offset < length; ) {
   final int codepoint = s.codePointAt(offset);

   // do something with the codepoint

   offset += Character.charCount(codepoint);
}

Problem

So I know about `String#codePointAt(int)`, but it's indexed by the `char` offset, not by the codepoint offset. I'm thinking about trying something like: - using `String#charAt(int)` to get the `char` at an index - testing whether the `char` is in the high-surrogates range - if so, use `String#codePointAt(int)` to get the codepoint, and increment the index by 2 - if not, use the given `char` value as the codepoint, and increment the index by 1 But my concerns are - I'm not sure whether codepoints which are naturally in the high-surrogates range will be stored as two `char` values or one - this seems like an awful expensive way to iterate through characters - someone must have come up with something better.

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