Iterator<String> nonpeek = Lists.newArrayList("a", "b", "c").iterator();
    PeekingIterator<String> peek = Iterators.peekingIterator(nonpeek);
    assertNotSame(peek, nonpeek);
    assertSame(peek, Iterators.peekingIterator(peek));
    assertSame(peek, Iterators.peekingIterator((Iterator<String>) peek));
  }

    public boolean offer(E e) {
      synchronized (mutex) {
        return delegate().offer(e);
      }
    }

    @Override
    @CheckForNull
    public E peek() {
      synchronized (mutex) {
        return delegate().peek();
      }
    }

    @Override
    @CheckForNull
    public E poll() {
      synchronized (mutex) {
        return delegate().poll();
      }
    }

  @Override
  public boolean isEmpty() {
    /*
     * Sum per-segment modCounts to avoid mis-reporting when elements are concurrently added and
     * removed in one segment while checking another, in which case the table was never actually
     * empty at any point. (The sum ensures accuracy up through at least 1<<31 per-segment
     * modifications before recheck.)  Method containsValue() uses similar constructions for

                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");
                    } catch (IllegalArgumentException expected) {
                    }
                    capturedPeeker.set(peeker);
                    return closeable2;

        return i;
      }
    }
    return -1;
  }

  /**
   * Returns the number of matching {@code char}s found in a character sequence.
   *
   * <p>Counts 2 per supplementary character, such as for {@link #whitespace}().{@link #negate}().
   */
  public int countIn(CharSequence sequence) {
    int count = 0;
    for (int i = 0; i < sequence.length(); i++) {

   * {@code combinations} does not retain the individual subsets.
   *
   * @param set the set of elements to take combinations of
   * @param size the number of elements per combination
   * @return the set of all combinations of {@code size} elements from {@code set}
   * @throws IllegalArgumentException if {@code size} is not between 0 and {@code set.size()}
   *     inclusive

    Iterator<String> nonpeek = Lists.newArrayList("a", "b", "c").iterator();
    PeekingIterator<String> peek = Iterators.peekingIterator(nonpeek);
    assertNotSame(peek, nonpeek);
    assertSame(peek, Iterators.peekingIterator(peek));
    assertSame(peek, Iterators.peekingIterator((Iterator<String>) peek));
  }

                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");
                    } catch (IllegalArgumentException expected) {
                    }
                    capturedPeeker.set(peeker);
                    return closeable2;

   * once after loading completes). Much internal cache management is performed at the segment
   * granularity. For example, access queues and write queues are kept per segment when they are
   * required by the selected eviction algorithm. As such, when writing unit tests it is not
   * uncommon to specify {@code concurrencyLevel(1)} in order to achieve more deterministic eviction
   * behavior.

        return i;
      }
    }
    return -1;
  }

  /**
   * Returns the number of matching {@code char}s found in a character sequence.
   *
   * <p>Counts 2 per supplementary character, such as for {@link #whitespace}().{@link #negate}().
   */
  public int countIn(CharSequence sequence) {
    int count = 0;
    for (int i = 0; i < sequence.length(); i++) {