f.addCallback(
        new FutureCallback<String>() {
          @Override
          public void onSuccess(String result) {
            called[0] = true;
          }

          @Override
          public void onFailure(Throwable t) {}
        },
        directExecutor());
    assertThat(called[0]).isTrue();
  }

  // Avoid trouble with automatic mapping between JRE and Kotlin runtime classes.

    f.addCallback(
        new FutureCallback<String>() {
          @Override
          public void onSuccess(String result) {
            called[0] = true;
          }

          @Override
          public void onFailure(Throwable t) {}
        },
        directExecutor());
    assertThat(called[0]).isTrue();
  }

  // Avoid trouble with automatic mapping between JRE and Kotlin runtime classes.