// null versus non-null.
    a = Arrays.<@Nullable Integer>asList(4, 8, 15, null, 23, 42);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a.iterator(), b.iterator()));
    assertFalse(elementsEqual(b.iterator(), a.iterator()));

    // Different lengths.
    a = asList(4, 8, 15, 16, 23);
    b = asList(4, 8, 15, 16, 23, 42);

    b = asList(4, 8, 15, 16, 23, 42);
    assertTrue(elementsEqual(a, b));

    // An element differs.
    a = asList(4, 8, 15, 12, 23, 42);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a, b));

    // null versus non-null.
    a = Arrays.<@Nullable Integer>asList(4, 8, 15, null, 23, 42);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a, b));
    assertFalse(elementsEqual(b, a));

   * number of elements and every element of {@code iterable1} is equal to the corresponding element
   * of {@code iterable2}.
   */
  public static boolean elementsEqual(Iterable<?> iterable1, Iterable<?> iterable2) {
    if (iterable1 instanceof Collection && iterable2 instanceof Collection) {
      Collection<?> collection1 = (Collection<?>) iterable1;