/**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableSortedMap} whose
   * keys and values are the result of applying the provided mapping functions to the input
   * elements. The generated map is sorted by the natural ordering of the keys.
   *
   * <p>If the mapped keys contain duplicates, an {@code IllegalArgumentException} is thrown when

      this.keys = new @Nullable Object[initialCapacity];
      this.values = new @Nullable Object[initialCapacity];
    }

    private void ensureCapacity(int minCapacity) {
      if (minCapacity > keys.length) {
        int newCapacity = ImmutableCollection.Builder.expandedCapacity(keys.length, minCapacity);
        this.keys = Arrays.copyOf(keys, newCapacity);

 *
 * <p>This implementation is heavily derived from revision 1.96 of <a
 * href="http://tinyurl.com/ConcurrentHashMap">ConcurrentHashMap.java</a>.
 *
 * @param <K> the type of the keys in the map
 * @param <V> the type of the values in the map
 * @param <E> the type of the {@link InternalEntry} entry implementation used internally
 * @param <S> the type of the {@link Segment} entry implementation used internally

      return unmodifiableValueCollection(delegate.get(key));
    }

    @Override
    public Multiset<K> keys() {
      Multiset<K> result = keys;
      if (result == null) {
        keys = result = Multisets.unmodifiableMultiset(delegate.keys());
      }
      return result;
    }

    @Override
    public Set<K> keySet() {
      Set<K> result = keySet;

      return unmodifiableValueCollection(delegate.get(key));
    }

    @Override
    public Multiset<K> keys() {
      Multiset<K> result = keys;
      if (result == null) {
        keys = result = Multisets.unmodifiableMultiset(delegate.keys());
      }
      return result;
    }

    @Override
    public Set<K> keySet() {
      Set<K> result = keySet;

 *
 * <p>This implementation is heavily derived from revision 1.96 of <a
 * href="http://tinyurl.com/ConcurrentHashMap">ConcurrentHashMap.java</a>.
 *
 * @param <K> the type of the keys in the map
 * @param <V> the type of the values in the map
 * @param <E> the type of the {@link InternalEntry} entry implementation used internally
 * @param <S> the type of the {@link Segment} entry implementation used internally

 *
 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the {@link
 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
 * comparisons for values.
 *

            return new Object();
          }

          @Override
          public Map<Object, Object> loadAll(Iterable<?> keys) throws Exception {
            Map<Object, Object> result = new HashMap<>();
            for (Object key : keys) {
              Object value = new Object();
              result.put(key, value);
              // add extra entries
              result.put(value, key);

 *
 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the {@link
 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
 * comparisons for values.
 *

            return new Object();
          }

          @Override
          public Map<Object, Object> loadAll(Iterable<?> keys) throws Exception {
            Map<Object, Object> result = new HashMap<>();
            for (Object key : keys) {
              Object value = new Object();
              result.put(key, value);
              // add extra entries
              result.put(value, key);