* elements in {@code a}, followed by the elements in {@code b}, followed by the elements in
   * {@code c}. The source iterators are not polled until necessary.
   *
   * <p>The returned iterator supports {@code remove()} when the corresponding input iterator
   * supports it.
   */
  public static <T extends @Nullable Object> Iterator<T> concat(

        return set1.isEmpty() && set2.isEmpty();
      }

      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<? extends E> itr1 = set1.iterator();
          final Iterator<? extends E> itr2 = set2.iterator();

          @Override
          @CheckForNull
          protected E computeNext() {
            if (itr1.hasNext()) {

  }

  public void testSize1() {
    Iterator<Integer> iterator = singleton(0).iterator();
    assertEquals(1, Iterators.size(iterator));
  }

  public void testSize_partiallyConsumed() {
    Iterator<Integer> iterator = asList(1, 2, 3, 4, 5).iterator();
    iterator.next();
    iterator.next();
    assertEquals(3, Iterators.size(iterator));
  }

  }

  public void testSize1() {
    Iterator<Integer> iterator = singleton(0).iterator();
    assertEquals(1, Iterators.size(iterator));
  }

  public void testSize_partiallyConsumed() {
    Iterator<Integer> iterator = asList(1, 2, 3, 4, 5).iterator();
    iterator.next();
    iterator.next();
    assertEquals(3, Iterators.size(iterator));
  }

  @ParameterizedTest
  @ArgumentsSource(FileSystemParamProvider::class)
  fun iterator(parameters: Pair<FileSystem, Boolean>) {
    setUp(parameters.first, parameters.second)
    set("a", "a1", "a2")
    set("b", "b1", "b2")
    set("c", "c1", "c2")
    val iterator = cache.snapshots()
    assertThat(iterator.hasNext()).isTrue()
    iterator.next().use {
      assertThat(it.key()).isEqualTo("a")

      }

      int oldCount = values.size();
      if (occurrences >= oldCount) {
        values.clear();
      } else {
        Iterator<V> iterator = values.iterator();
        for (int i = 0; i < occurrences; i++) {
          iterator.next();
          iterator.remove();
        }
      }
      return oldCount;
    }

    @Override
    public void clear() {
      multimap.clear();

    @Override
    public boolean removeAll(Collection<?> c) {
      synchronized (mutex) {
        return Iterators.removeAll(delegate().iterator(), c);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      synchronized (mutex) {
        return Iterators.retainAll(delegate().iterator(), c);
      }
    }

    private static final long serialVersionUID = 0;
  }

    @Override
    public boolean removeAll(Collection<?> c) {
      synchronized (mutex) {
        return Iterators.removeAll(delegate().iterator(), c);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      synchronized (mutex) {
        return Iterators.retainAll(delegate().iterator(), c);
      }
    }

    private static final long serialVersionUID = 0;
  }

  @Override
  public Set<Entry<K, V>> entrySet() {
    Set<Entry<K, V>> es = entrySet;
    return (es != null) ? es : (entrySet = new EntrySet());
  }

  // Iterator Support

  abstract class HashIterator<T> implements Iterator<T> {

    int nextSegmentIndex;
    int nextTableIndex;
    @CheckForNull Segment<K, V, E, S> currentSegment;
    @CheckForNull AtomicReferenceArray<E> currentTable;

  @Override
  public Set<Entry<K, V>> entrySet() {
    Set<Entry<K, V>> es = entrySet;
    return (es != null) ? es : (entrySet = new EntrySet());
  }

  // Iterator Support

  abstract class HashIterator<T> implements Iterator<T> {

    int nextSegmentIndex;
    int nextTableIndex;
    @CheckForNull Segment<K, V, E, S> currentSegment;
    @CheckForNull AtomicReferenceArray<E> currentTable;