* We use `fromNullable` instead of `of` because `WeakReference.get()` has a nullable return
     * type.
     *
     * In practice, we are very unlikely to see `null`: The `WeakReference` to the enum constant
     * won't be cleared as long as the enum constant is referenced somewhere, and the enum constant
     * is referenced somewhere for as long as the enum class is loaded. *Maybe in theory* the enum

       * pass.
       *
       * 2. We would probably choose to compare exceptions using == instead of equals() (for
       * consistency with how weak references are cleared). That's a behavior change -- arguably the
       * removal of a feature.
       *
       * Fortunately, exceptions rarely contain references to expensive resources.
       */

      //

    }

    public void test_clearCache() {
        // Test that clearCache doesn't throw exception
        popularWordHelper.clearCache();

        // Verify cache is cleared (we can't directly test this without accessing the cache)
        // But we can test that it doesn't throw exceptions
        assertTrue(true);
    }

    public void test_init_configuration() {

    assertEquals(1, segment.count);
    assertSame(newValue, segment.get(key, hash));

    // cleared
    entry.setValueReference(oldValueRef);
    assertSame(oldValue, segment.get(key, hash));
    oldValueRef.clear();
    assertFalse(segment.replace(key, hash, oldValue, newValue));
    assertEquals(0, segment.count);
    assertNull(segment.get(key, hash));
  }

   * clear()} clears all table mappings.
   */
  @WeakOuter
  private abstract class TableSet<T> extends ImprovedAbstractSet<T> {
    @Override
    public boolean isEmpty() {
      return backingMap.isEmpty();
    }

    @Override
    public void clear() {
      backingMap.clear();
    }
  }

  /**
   * {@inheritDoc}
   *

        for (WeakReference<Class<? extends Exception>> knownGood : validClasses) {
          if (exceptionClass.equals(knownGood.get())) {
            return;
          }
          // TODO(cpovirk): if reference has been cleared, remove it?
        }
        checkExceptionClassValidity(exceptionClass);

        /*
         * It's very unlikely that any loaded Futures class will see getChecked called with more

        for (WeakReference<Class<? extends Exception>> knownGood : validClasses) {
          if (exceptionClass.equals(knownGood.get())) {
            return;
          }
          // TODO(cpovirk): if reference has been cleared, remove it?
        }
        checkExceptionClassValidity(exceptionClass);

        /*
         * It's very unlikely that any loaded Futures class will see getChecked called with more

        }
        /*
         * requireNonNull is safe: The first call to this method always enters the !hasNext() case
         * and populates currentKey, after which it's never cleared.
         */
        return immutableEntry(requireNonNull(currentKey), valueItr.next());
      }
    };
  }

  @Override
  Spliterator<Entry<K, V>> entrySpliterator() {

    totalSize -= collection.size();
    collection.clear();

    return unmodifiableCollectionSubclass(output);
  }

  <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    return Collections.unmodifiableCollection(collection);
  }

  @Override
  public void clear() {
    // Clear each collection, to make previously returned collections empty.

      executorService.execute(
          () -> {
            lock.lock();
            try {
              startUp();
              /*
               * requireNonNull is safe because executorService is never cleared after the
               * assignment above.
               */
              requireNonNull(executorService);
              runningTask = scheduler().schedule(delegate, executorService, task);