private final List<Thread> hooks = Lists.newArrayList();

    @Override
    synchronized void addShutdownHook(Thread hook) {
      hooks.add(hook);
    }

    synchronized void shutdown() throws InterruptedException {
      for (Thread hook : hooks) {
        hook.start();
      }
      for (Thread hook : hooks) {
        hook.join();
      }
    }
  }

    private final List<Thread> hooks = Lists.newArrayList();

    @Override
    synchronized void addShutdownHook(Thread hook) {
      hooks.add(hook);
    }

    synchronized void shutdown() throws InterruptedException {
      for (Thread hook : hooks) {
        hook.start();
      }
      for (Thread hook : hooks) {
        hook.join();
      }
    }
  }

                    // following code, but unfortunately the behavior of logging
                    // is undefined in shutdown hooks.
                    // This is because the logging code installs a shutdown hook of its
                    // own. See Cleaner class inside {@link LogManager}.
                    service.shutdown();

     * already have to deal with, thanks to DI frameworks that perform field and method injection,
     * frameworks like Android that define post-construct hooks like Activity.onCreate, etc.
     */

    @CheckForNull private ValueSetLink<K, V> predecessorInValueSet;
    @CheckForNull private ValueSetLink<K, V> successorInValueSet;

    }

    public static OptionalEntity<StopwordsItem> createStopwordsItem(final CreateForm form, final VaErrorHook hook) {
        return getEntity(form).map(entity -> {
            final String newInput = form.input;
            validateStopwordsString(newInput, "input", hook);
            entity.setNewInput(newInput);
            return entity;
        });
    }

    protected WebConfigService webConfigService;

    // ===================================================================================
    //                                                                               Hook
    //                                                                              ======
    @Override
    protected void setupHtmlData(final ActionRuntime runtime) {
        super.setupHtmlData(runtime);

    protected DynamicProperties systemProperties;

    // ===================================================================================
    //                                                                               Hook
    //                                                                              ======
    @Override
    protected void setupHtmlData(final ActionRuntime runtime) {
        super.setupHtmlData(runtime);

    protected ScheduledJobService scheduledJobService;

    // ===================================================================================
    //                                                                               Hook
    //                                                                              ======
    @Override
    protected void setupHtmlData(final ActionRuntime runtime) {
        super.setupHtmlData(runtime);

 *
 * <pre>
 * interface Book {...}
 * public class Books {
 *   public static Book hardcover(String title) {...}
 *   public static Book paperback(String title) {...}
 * }
 * </pre>
 *
 * <p>And all the created {@code Book} instances can be tested with:
 *
 * <pre>
 * new ClassSanityTester()
 *     .forAllPublicStaticMethods(Books.class)
 *     .thatReturn(Book.class)

    protected WebConfigService webConfigService;

    // ===================================================================================
    //                                                                               Hook
    //                                                                              ======
    @Override
    protected void setupHtmlData(final ActionRuntime runtime) {
        super.setupHtmlData(runtime);