assertTrue(broken.hasNext());
    // We can't retrieve even the known first element:
    assertThrows(SomeUncheckedException.class, broken::next);
    assertThrows(SomeUncheckedException.class, broken::next);
  }

  private static Iterator<Integer> newDoubler(int first, int last) {
    return new AbstractSequentialIterator<Integer>(first) {
      @Override
      protected @Nullable Integer computeNext(Integer previous) {

  @CanIgnoreReturnValue
  public final <A extends Appendable> A appendTo(
      A appendable, @Nullable Object first, @Nullable Object second, @Nullable Object... rest)
      throws IOException {
    return appendTo(appendable, iterable(first, second, rest));
  }

  /**
   * Appends the string representation of each of {@code parts}, using the previously configured

   *
   * @param first the first array of elements to concatenate
   * @param second the second array of elements to concatenate
   * @param type the component type of the returned array
   */
  @GwtIncompatible // Array.newInstance(Class, int)
  public static <T extends @Nullable Object> T[] concat(
      T[] first, T[] second, Class<@NonNull T> type) {

        // List with first element NOT being Entity
        List<Object> mixedList = new ArrayList<>();
        mixedList.add("string first");
        mixedList.add(entity);

        RenderDataUtil.register(data, "mixed", mixedList);

        Object result = data.getDataMap().get("mixed");
        assertEquals(mixedList, result); // Should be registered as-is since first element is not Entity
    }

        // Should alternate between channels
        ChannelInfo first = loadBalancer.selectChannel(mockMessage);
        ChannelInfo second = loadBalancer.selectChannel(mockMessage);

        assertNotNull(first);
        assertNotNull(second);
        // Due to round-robin, should get different channels or same order
        assertTrue(Arrays.asList(channel1, channel2).contains(first));

$(function() {
  $('input[type="text"],select,textarea', ".login-box,section.content")
    .first()
    .focus();
  $(".form-group .has-error")
    .first()
    .next("input,select,textarea")
    .focus();

  $("section.content input").keypress(function(e) {
    var $submitButton;
    if (e.which === 13) {
      $submitButton = $("input#submit, button#submit");
      if ($submitButton.length > 0) {
        $submitButton[0].submit();
      }

/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first { #read-the-tutorial-first }

The next sections assume you already read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

    Converter<StringWrapper, Long> converter = first.andThen(STR_TO_LONG);

    assertEquals(LONG_VAL, converter.convert(new StringWrapper(STR_VAL)));
    assertEquals(STR_VAL, converter.reverse().convert(LONG_VAL).value);

    assertEquals("StringWrapper.andThen(string2long)", converter.toString());

    new EqualsTester()
        .addEqualityGroup(first.andThen(STR_TO_LONG), first.andThen(STR_TO_LONG))
        .testEquals();
  }

            },
            directExecutor());

    // Wait for the first task to be started in the background. It will block until we explicitly
    // stop it.
    blockingCallable.waitForStart();

    // Give the second task a chance to (incorrectly) start up while the first task is running.
    assertThat(future2.isDone()).isFalse();

    // Stop the first task. The second task should then run.
    blockingCallable.stop();

/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

## Read the Tutorial first { #read-the-tutorial-first }

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.