guava/src/com/google/common/eventbus/SubscriberRegistry.java
@VisibleForTesting
  static ImmutableSet<Class<?>> flattenHierarchy(Class<?> concreteClass) {
    try {
      return flattenHierarchyCache.getUnchecked(concreteClass);
    } catch (UncheckedExecutionException e) {
      throw Throwables.propagate(e.getCause());
    }
  }
@VisibleForTesting
  static ImmutableSet<Class<?>> flattenHierarchy(Class<?> concreteClass) {
    try {
      return flattenHierarchyCache.getUnchecked(concreteClass);
    } catch (UncheckedExecutionException e) {
      throw Throwables.propagate(e.getCause());
    }
  }
Flattens a class's type hierarchy into a set of {@code Class} objects including all
superclasses (transitively) and all interfaces implemented by these superclasses.