gc timings fixed

SortMojis.java

import java.math.BigInteger;
import java.text.NumberFormat;
import java.util.*;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class SortMojis {
    private static final NumberFormat NUM_FMT = NumberFormat.getNumberInstance(Locale.JAPAN);
    private static final String kanjis = "\uD842\uDFB7\uD867\uDE3D";
    private static final String emojis =
            "\uD83D\uDC7B\uD83D\uDC69\u200D\uD83D\uDC69\u200D\uD83D\uDC66\u200D\uD83D\uDC66".repeat(2);
    private static final int COUNT = BigInteger.valueOf(10).pow(7).intValue();
    public static final Pattern GRAPHEME_CLUSTER_BOUNDARY = Pattern.compile("\\b{g}");
    private static final String[] manyEmojis = GRAPHEME_CLUSTER_BOUNDARY.split(emojis.repeat(COUNT));

    public static long measureNanoTime(Runnable r) {
        final long start = System.nanoTime();
        r.run();
        final long end = System.nanoTime();
        return end - start;
    }

    private static String sortDesc(String str) {
        char[] chars = str.toCharArray();
        Arrays.sort(chars);
        StringBuilder sb = new StringBuilder(chars.length);
        sb.append(chars);
        return sb.reverse().toString();
    }

    public static void main(String[] args) {
        {
            System.out.println("Sorting surrogate pair Han characters (broken)");
            String reversed = sortDesc(kanjis);
            System.out.println(reversed);
        }
        {
            System.out.println("Sorting surrogate pair Han characters");
            String reversed = kanjis.codePoints().boxed().sorted(Comparator.reverseOrder())
                    .collect(
                            () -> new StringBuilder(),
                            (sb, i) -> sb.appendCodePoint(i),
                            (sb1, sb2) -> sb1.append(sb2)
                    ).toString();
            System.out.println(reversed);
        }
        {
            System.out.println("Sorting emojis (broken)");
            String reversed = emojis.codePoints().boxed().sorted(Comparator.reverseOrder())
                    .collect(
                            () -> new StringBuilder(),
                            (sb, i) -> sb.appendCodePoint(i),
                            (sb1, sb2) -> sb1.append(sb2)
                    ).toString();
            System.out.println(reversed);
        }
        {
            System.out.println("Sorting emojis");
            String reversed = Arrays.stream(GRAPHEME_CLUSTER_BOUNDARY.split(emojis))
                    .sorted(Comparator.reverseOrder())
                    .collect(Collectors.joining());
            System.out.println(reversed);
        }
        {
            System.out.println("parallelSort and then reverse");
            String[] arr = manyEmojis.clone();
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                Arrays.parallelSort(arr);
                List<String> list = Arrays.asList(arr);
                Collections.reverse(list);
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("parallelSort reversedOrder");
            String[] arr = manyEmojis.clone();
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                Arrays.parallelSort(arr, Comparator.reverseOrder());
                String reversed = String.join("", arr);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("sort and then reverse");
            String[] arr = manyEmojis.clone();
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                Arrays.sort(arr);
                List<String> list = Arrays.asList(arr);
                Collections.reverse(list);
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("sort reversedOrder");
            String[] arr = manyEmojis.clone();
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                Arrays.sort(arr, Comparator.reverseOrder());
                String reversed = String.join("", arr);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("parallel Stream reversedOrder");
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                List<String> list = Arrays.stream(manyEmojis).parallel()
                        .sorted(Comparator.reverseOrder())
                        .collect(Collectors.toList());
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("sort the parallel Stream and then collect to a list and then reverse it");
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                List<String> list = Arrays.stream(manyEmojis).parallel()
                        .sorted()
                        .collect(Collectors.toList());
                Collections.reverse(list);
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("Stream reversedOrder");
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                List<String> list = Arrays.stream(manyEmojis)
                        .sorted(Comparator.reverseOrder())
                        .collect(Collectors.toList());
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
        System.gc();
        {
            System.out.println("sort the Stream and then collect to a list and then reverse it");
            System.out.println(NUM_FMT.format(measureNanoTime(() -> {
                List<String> list = Arrays.stream(manyEmojis)
                        .sorted()
                        .collect(Collectors.toList());
                Collections.reverse(list);
                String reversed = String.join("", list);
                System.out.println("length: " + reversed.length());
            })));
        }
    }
}