How to Efficiently Iterate Over Unicode Codepoints in Java Strings?

Iterating over Unicode Codepoints in Java Strings

While the String class provides the codePointAt(int) method for accessing Unicode codepoints, its indexing relies on character offsets rather than codepoint offsets. This raises concerns about handling characters within the high-surrogate range and the efficiency of the proposed iteration approach using character-by-character scanning.

Improved Iteration Solution

Java's internal String representation employs a UTF-16-based encoding scheme. Characters outside the Basic Multilingual Plane (BMP) are encoded using the surrogacy scheme. For efficient iteration, consider using the following canonical approach:

<code class="java">final int length = s.length();
for (int offset = 0; offset < length; ) {
   final int codepoint = s.codePointAt(offset);

   // process the codepoint

   offset += Character.charCount(codepoint);
}</code>

This approach correctly handles surrogate pairs for characters outside the BMP. By utilizing Character.charCount(codepoint), it efficiently increments the offset by the appropriate number of characters for each codepoint.

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