checkNotNull(iterable);
    Iterators.checkNonnegative(position);
    if (iterable instanceof List) {
      List<? extends T> list = Lists.cast(iterable);
      return (position < list.size()) ? list.get(position) : defaultValue;
    } else {
      Iterator<? extends T> iterator = iterable.iterator();
      Iterators.advance(iterator, position);
      return Iterators.getNext(iterator, defaultValue);
    }
  }

    assertEquals(1, Iterators.size(registry.getSubscribers(1)));

    registry.register(new IntegerSubscriber());
    assertEquals(3, Iterators.size(registry.getSubscribers("")));
    assertEquals(1, Iterators.size(registry.getSubscribers(new Object())));
    assertEquals(2, Iterators.size(registry.getSubscribers(1)));
  }

  public void testGetSubscribers_returnsImmutableSnapshot() {

All `go/types` data structures that expose sequences using a pair of
methods such as `Len() int` and `At(int) T` now also methods that
return iterators, allowing you to simplify code such as this:

```go
params := fn.Type.(*types.Signature).Params()
for i := 0; i < params.Len(); i++ {
   use(params.At(i))
}
```

to this:

```go
for param := range fn.Signature().Params().Variables() {
   use(param)
}
```

            if (graph.isDirected()) {
              return Iterators.unmodifiableIterator(
                  Iterators.concat(
                      Iterators.transform(
                          graph.predecessors(node).iterator(),
                          (N predecessor) -> EndpointPair.ordered(predecessor, node)),
                      Iterators.transform(

        @Override
        protected Set<K> delegate() {
          return delegate.keySet();
        }

        @Override
        public Iterator<K> iterator() {
          return Iterators.unmodifiableIterator(delegate.keySet().iterator());
        }

        @Override
        public boolean removeAll(Collection<?> c) {
          return delegate.keySet().removeAll(c);
        }

        @Override

    List<?> list = emptyList();
    Iterator<?> iterator = list.iterator();
    PeekingIterator<?> peekingIterator = Iterators.peekingIterator(iterator);

    assertThrows(NoSuchElementException.class, () -> peekingIterator.peek());
  }

  public void testPeekDoesntChangeIteration() {
    List<?> list = Lists.newArrayList("A", "B", "C");
    Iterator<?> iterator = list.iterator();

  public Entry<K, V> firstEntry() {
    return Iterators.<@Nullable Entry<K, V>>getNext(entryIterator(), null);
  }

  @Override
  @CheckForNull
  public Entry<K, V> lastEntry() {
    return Iterators.<@Nullable Entry<K, V>>getNext(descendingEntryIterator(), null);
  }

  @Override
  @CheckForNull
  public Entry<K, V> pollFirstEntry() {
    return Iterators.pollNext(entryIterator());
  }

  @Override

  protected E standardHigher(@ParametricNullness E e) {
    return Iterators.getNext(tailSet(e, false).iterator(), null);
  }

  @Override
  @CheckForNull
  public E pollFirst() {
    return delegate().pollFirst();
  }

  /**
   * A sensible definition of {@link #pollFirst} in terms of the {@code iterator} method. If you
   * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this

      @Override
      public Iterator<T> iterator() {
        return Iterators.concat(
            /* lazily generate the iterators on each input only as needed */
            new AbstractIndexedListIterator<Iterator<? extends T>>(inputs.length) {
              @Override
              public Iterator<? extends T> get(int i) {
                return inputs[i].iterator();
              }
            });
      }

The [strings] package adds several functions that work with iterators:
- [Lines] returns an iterator over
  the newline-terminated lines in the string s.
- [SplitSeq] returns an iterator over
  all substrings of s separated by sep.
- [SplitAfterSeq] returns an iterator
  over substrings of s split after each instance of sep.
- [FieldsSeq] returns an iterator over
  substrings of s split around runs of whitespace characters,
  as defined by unicode.IsSpace.