public static <T extends @Nullable Object> UnmodifiableIterator<T> unmodifiableIterator(
      Iterator<? extends T> iterator) {
    checkNotNull(iterator);
    if (iterator instanceof UnmodifiableIterator) {
      @SuppressWarnings("unchecked") // Since it's unmodifiable, the covariant cast is safe
      UnmodifiableIterator<T> result = (UnmodifiableIterator<T>) iterator;
      return result;
    }

      throw new UnsupportedOperationException();
    }

    /**
     * Scope the return type to {@link UnmodifiableIterator} to ensure this is an unmodifiable view.
     *
     * @since 20.0 (present with return type {@link Iterator} since 2.0)
     */
    @Override
    public abstract UnmodifiableIterator<E> iterator();
  }

  /**

    Iterator<String> mod = Lists.newArrayList("a", "b", "c").iterator();
    UnmodifiableIterator<String> unmod = Iterators.unmodifiableIterator(mod);
    assertNotSame(mod, unmod);
    assertSame(unmod, Iterators.unmodifiableIterator(unmod));
    assertSame(unmod, Iterators.unmodifiableIterator((Iterator<String>) unmod));
  }

  @SuppressWarnings("deprecation")

    Iterator<String> mod = Lists.newArrayList("a", "b", "c").iterator();
    UnmodifiableIterator<String> unmod = Iterators.unmodifiableIterator(mod);
    assertNotSame(mod, unmod);
    assertSame(unmod, Iterators.unmodifiableIterator(unmod));
    assertSame(unmod, Iterators.unmodifiableIterator((Iterator<String>) unmod));
  }

  @SuppressWarnings("deprecation")

    return super.entrySet();
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    class EntrySet extends ImmutableMapEntrySet<K, V> {
      @Override
      public UnmodifiableIterator<Entry<K, V>> iterator() {
        return asList().iterator();
      }

      @Override
      public Spliterator<Entry<K, V>> spliterator() {
        return asList().spliterator();
      }

    return super.entrySet();
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    class EntrySet extends ImmutableMapEntrySet<K, V> {
      @Override
      public UnmodifiableIterator<Entry<K, V>> iterator() {
        return asList().iterator();
      }

      @Override
      ImmutableList<Entry<K, V>> createAsList() {
        return new ImmutableList<Entry<K, V>>() {