GraphemesTest.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

class GraphemesTest {

    public static void main(String[] args) throws IOException {
        analyzeResult("чернокожий человек делает фейспалм");
        analyzeResult("чернокожий мужчина делает фейспалм");
        analyzeResult("family");
    }

    private static void analyzeResult(String fileName) throws IOException {
        byte[] bytes = readTmp(fileName + ".txt");
        var result = new String(bytes).strip();
        System.out.printf("`%s` bytes: [%d]\n", fileName, bytes.length);
        System.out.printf("`%s` in chars: [%d]\n", fileName, result.toCharArray().length);
        System.out.printf("`%s` in codePoints: [%d]\n", fileName, result.codePoints().toArray().length);
        System.out.printf("`%s`.length(): [%d]\n", fileName, result.length());
        System.out.printf("`%s`: %s\n", fileName, result);
        System.out.printf("`%s` reversed: %s\n", fileName, new StringBuilder(result).reverse().toString());
    }

    private static byte[] readTmp(String txt) throws IOException {
        return Files.readAllBytes(Path.of(System.getProperty("user.home"), "tmp", txt));
    }

}