assertEquals(newArrayList("a", "c", "e"), list);
  }

  public void testRemoveIf() {
    List<String> list = newArrayList("a", "b", "c", "d", "e");
    assertTrue(
        Iterators.removeIf(
            list.iterator(),
            new Predicate<String>() {
              @Override
              public boolean apply(String s) {
                return s.equals("b") || s.equals("d") || s.equals("f");

    assertEquals(newArrayList("a", "c", "e"), list);
  }

  public void testRemoveIf() {
    List<String> list = newArrayList("a", "b", "c", "d", "e");
    assertTrue(
        Iterators.removeIf(
            list.iterator(),
            new Predicate<String>() {
              @Override
              public boolean apply(String s) {
                return s.equals("b") || s.equals("d") || s.equals("f");

      synchronized (mutex) {
        return delegate().retainAll(c);
      }
    }

    @Override
    public boolean removeIf(Predicate<? super E> filter) {
      synchronized (mutex) {
        return delegate().removeIf(filter);
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    @DoNotCall("Always throws UnsupportedOperationException")
    public final boolean removeIf(java.util.function.Predicate<? super E> filter) {
      throw new UnsupportedOperationException();
    }

    /**
     * Guaranteed to throw an exception and leave the collection unmodified.
     *

   * @return {@code true} if any elements were removed from the iterator
   * @since 2.0
   */
  @CanIgnoreReturnValue
  public static <T extends @Nullable Object> boolean removeIf(
      Iterator<T> removeFrom, Predicate<? super T> predicate) {
    checkNotNull(predicate);
    boolean modified = false;
    while (removeFrom.hasNext()) {
      if (predicate.apply(removeFrom.next())) {

   * @return {@code true} if any elements were removed from the iterator
   * @since 2.0
   */
  @CanIgnoreReturnValue
  public static <T extends @Nullable Object> boolean removeIf(
      Iterator<T> removeFrom, Predicate<? super T> predicate) {
    checkNotNull(predicate);
    boolean modified = false;
    while (removeFrom.hasNext()) {
      if (predicate.apply(removeFrom.next())) {