return seq.length() - pos;
  }

  /*
   * To avoid the need to call requireNonNull so much, we could consider more clever approaches,
   * such as:
   *
   * - Make checkOpen return the non-null `seq`. Then callers can assign that to a local variable or
   *   even back to `this.seq`. However, that may suggest that we're defending against concurrent
   *   mutation, which is not an actual risk because we use `synchronized`.

   * nulls as long as the *last* element is *not* null.
   *
   * (To "go out of its way," the method tracks a `set` bit so that it can distinguish "the final
   * split has a last element of null, so throw NPE" from "the final split was empty, so look for an
   * element in the prior one.")
   */
  public static <T> java.util.Optional<T> findLast(Stream<T> stream) {

import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import java.util.concurrent.Executor;
import java.util.logging.Level;
import org.jspecify.annotations.Nullable;

/**
 * A support class for {@code ListenableFuture} implementations to manage their listeners. An

    Hash {
      @Override
      Map<Element, Element> create(Collection<Element> keys) {
        Map<Element, Element> map = new HashMap<>();
        for (Element element : keys) {
          map.put(element, element);
        }
        return map;
      }
    },
    LinkedHM {
      @Override
      Map<Element, Element> create(Collection<Element> keys) {
        Map<Element, Element> map = new LinkedHashMap<>();

import static java.lang.Character.MAX_SURROGATE;
import static java.lang.Character.MIN_SURROGATE;

import com.google.common.annotations.GwtCompatible;

/**
 * Low-level, high-performance utility methods related to the {@linkplain Charsets#UTF_8 UTF-8}
 * character encoding. UTF-8 is defined in section D92 of <a
 * href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core

import static java.lang.Character.MAX_SURROGATE;
import static java.lang.Character.MIN_SURROGATE;

import com.google.common.annotations.GwtCompatible;

/**
 * Low-level, high-performance utility methods related to the {@linkplain Charsets#UTF_8 UTF-8}
 * character encoding. UTF-8 is defined in section D92 of <a
 * href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core

        .createTestSuite();
  }

  // Not specifying KNOWN_ORDER for PriorityQueue and PriorityBlockingQueue
  // even though they do have it, because our tests interpret KNOWN_ORDER to
  // also mean that the iterator returns the head element first, which those
  // don't.

  public Test testsForPriorityBlockingQueue() {
    return QueueTestSuiteBuilder.using(

        final Entry entry = getEntry(index);
        final E oldValue = entry.element;
        entry.element = element;
        return oldValue;
    }

    /**
     * Returns the position of the element.
     *
     * @param element the element
     * @return the position
     */
    public int indexOf(final E element) {
        int index = 0;
        if (element == null) {

    final int hash;

    Element(int hash) {
      this.hash = hash;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return this == obj || (obj instanceof Element && ((Element) obj).hash == hash);
    }

    @Override
    public int hashCode() {
      return hash;
    }

    @Override
    public int compareTo(Element that) {

    /**
     * Returns the number of occurrences of {@code element} in this multiset.
     *
     * @param element the element to look for
     * @return the nonnegative number of occurrences of the element
     */
    @Override
    public int count(@Nullable Object element) {
      try {
        return unbox(countMap.get(element));
      } catch (NullPointerException | ClassCastException e) {
        return 0;