*
 * <p>A call to any of the <i>enter</i> methods with <b>void</b> return type should always be
 * followed immediately by a <i>try/finally</i> block to ensure that the current thread leaves the
 * monitor cleanly:
 *
 * <pre>{@code
 * monitor.enter();
 * try {
 *   // do things while occupying the monitor
 * } finally {
 *   monitor.leave();
 * }
 * }</pre>
 *

   *
   * <p>This method is similar to {@link java.util.concurrent.CompletableFuture#whenComplete} and
   * {@link java.util.concurrent.CompletableFuture#whenCompleteAsync}. It also serves the use case
   * of {@link java.util.concurrent.CompletableFuture#thenAccept} and {@link
   * java.util.concurrent.CompletableFuture#thenAcceptAsync}.
   *

   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this class leaves the specific choice of
   * hash code unspecified, unlike the Java 8+ equivalent.
   */
  @Override
  public abstract int hashCode();

  /**
   * Returns a string representation for this instance.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this class leaves the specific string

 * including those in many JDK classes.
 *
 * <p>{@code Object.hashCode} implementations tend to be very fast, but have weak collision
 * prevention and <i>no</i> expectation of bit dispersion. This leaves them perfectly suitable for
 * use in hash tables, because extra collisions cause only a slight performance hit, while poor bit
 * dispersion is easily corrected using a secondary hash function (which all reasonable hash table

    // (b) Waiting for the single guard to become satisfied.
    // (c) Occupying the monitor and awaiting the tearDownLatch.
    //
    // Except for (c), every thread should occupy the monitor very briefly, and every thread leaves
    // the monitor with the guard satisfied. Therefore as soon as tearDownLatch is triggered, we
    // should be able to enter the monitor, and then we set the guard to satisfied for the benefit

  @CheckForNull
  public E peekLast() {
    return isEmpty() ? null : elementData(getMaxElementIndex());
  }

  /**
   * Removes the element at position {@code index}.
   *
   * <p>Normally this method leaves the elements at up to {@code index - 1}, inclusive, untouched.
   * Under these circumstances, it returns {@code null}.
   *
   * <p>Occasionally, in order to maintain the heap invariant, it must swap a later element of the

    // (b) Waiting for the single guard to become satisfied.
    // (c) Occupying the monitor and awaiting the tearDownLatch.
    //
    // Except for (c), every thread should occupy the monitor very briefly, and every thread leaves
    // the monitor with the guard satisfied. Therefore as soon as tearDownLatch is triggered, we
    // should be able to enter the monitor, and then we set the guard to satisfied for the benefit

    //     imagine a line separating the first block from the second, we can proceed by exchanging
    //     the smaller of these blocks with the far end of the other one. That leaves us with a
    //     smaller version of the same problem.
    //     Say we are rotating abcdefgh by 5. We start with abcde|fgh. The smaller block is [fgh]:

   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this class leaves the specific choice of
   * hash code unspecified, unlike the Java 8+ equivalent.
   */
  @Override
  public abstract int hashCode();

  /**
   * Returns a string representation for this instance.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this class leaves the specific string