ListenableFuture<I> input,
      AsyncFunction<? super I, ? extends O> function,
      Executor executor) {
    AsyncTransformFuture<I, O> output = new AsyncTransformFuture<>(input, function);
    input.addListener(output, rejectionPropagatingExecutor(executor, output));
    return output;
  }

  static <I extends @Nullable Object, O extends @Nullable Object> ListenableFuture<O> create(

  // operation in the constructor.
  //
  // 1. In the listener that performs the callback. In this case it is fine since inputFuture is
  //    assigned prior to calling addListener, and addListener happens-before any invocation of the
  //    listener. Notably, this means that 'volatile' is unnecessary to make 'inputFuture' visible
  //    to the listener.
  //

   * service changes state. The listener will not have previous state changes replayed, so it is
   * suggested that listeners are added before the service starts.
   *
   * <p>{@code addListener} guarantees execution ordering across calls to a given listener but not
   * across calls to multiple listeners. Specifically, a given listener will have its callbacks

            return null;
        }

        @Override
        public void addListener(String className) {
        }

        @Override
        public <T extends java.util.EventListener> void addListener(T t) {
        }

        @Override
        public void addListener(Class<? extends java.util.EventListener> listenerClass) {
        }

        @Override

import java.util.concurrent.Executor;
import java.util.logging.Level;

/**
 * A list of listeners for implementing a concurrency friendly observable object.
 *
 * <p>Listeners are registered once via {@link #addListener} and then may be invoked by {@linkplain
 * #enqueue enqueueing} and then {@linkplain #dispatch dispatching} events.
 *
 * <p>The API of this class is designed to make it easy to achieve the following properties
 *
 * <ul>

            return null;
        }

        @Override
        public void addListener(String className) {
        }

        @Override
        public <T extends java.util.EventListener> void addListener(T t) {
        }

        @Override
        public void addListener(Class<? extends java.util.EventListener> listenerClass) {
        }

        @Override

      // Register a listener on each Future in the list to update the state of this future.
      // Note that if all the futures on the list are done prior to completing this loop, the last
      // call to addListener() will callback to setOneValue(), transitively call our cleanup
      // listener, and set this.futures to null.
      // This is not actually a problem, since the foreach only needs this.futures to be non-null

              }
              return 25;
            }
          });

  @Override
  protected void setUp() throws Exception {
    super.setUp();

    exec = newCachedThreadPool();

    task.addListener(
        new Runnable() {
          @Override
          public void run() {
            listenerLatch.countDown();
          }
        },
        directExecutor());
  }

  @Override

  private final ListenableFuture<?> future;

  public MockFutureListener(ListenableFuture<?> future) {
    this.countDownLatch = new CountDownLatch(1);
    this.future = future;

    future.addListener(this, directExecutor());
  }

  @Override
  public void run() {
    countDownLatch.countDown();
  }

  /**
   * Verify that the listener completes in a reasonable amount of time, and Asserts that the future

    this.exec = newCachedThreadPool();
    this.future = checkNotNull(future);
    this.latch = new CountDownLatch(1);
  }

  public void setUp() {
    future.addListener(
        new Runnable() {
          @Override
          public void run() {
            latch.countDown();
          }
        },
        exec);

    assertEquals(1, latch.getCount());