* Comparator} or {@link Comparable} type whose comparison behavior is <i>inconsistent with
 * equals</i>. That is, {@code a.compareTo(b)} or {@code comparator.compare(a, b)} should equal zero
 * <i>if and only if</i> {@code a.equals(b)}. If this advice is not followed, the resulting map will
 * not correctly obey its specification.
 *
 * <p>See the Guava User Guide article on <a href=

  private static final class Listener {
    static final Listener TOMBSTONE = new Listener();
    @CheckForNull // null only for TOMBSTONE
    final Runnable task;
    @CheckForNull // null only for TOMBSTONE
    final Executor executor;

    // writes to next are made visible by subsequent CAS's on the listeners field
    @CheckForNull Listener next;

        ImmutableMap.of(
            3, ValueDifferenceImpl.create("c", "f"), 5, ValueDifferenceImpl.create("e", "g")),
        diff1.entriesDiffering());
    assertEquals(
        "not equal: only on left={2=b, 4=d}: only on right={6=z}: "
            + "value differences={3=(c, f), 5=(e, g)}",
        diff1.toString());

    MapDifference<Integer, String> diff2 = Maps.difference(right, left);
    assertFalse(diff2.areEqual());

        ImmutableMap.of(
            3, ValueDifferenceImpl.create("c", "f"), 5, ValueDifferenceImpl.create("e", "g")),
        diff1.entriesDiffering());
    assertEquals(
        "not equal: only on left={2=b, 4=d}: only on right={6=z}: "
            + "value differences={3=(c, f), 5=(e, g)}",
        diff1.toString());

    MapDifference<Integer, String> diff2 = Maps.difference(right, left);
    assertFalse(diff2.areEqual());

  @GwtIncompatible // used only from other GwtIncompatible code
  private static final class BitSetMatcher extends NamedFastMatcher {

    private final BitSet table;

    private BitSetMatcher(BitSet table, String description) {
      super(description);
      if (table.length() + Long.SIZE < table.size()) {
        table = (BitSet) table.clone();
        // If only we could actually call BitSet.trimToSize() ourselves...

    testConcurrentLoading(CacheBuilder.newBuilder().expireAfterWrite(10, TimeUnit.SECONDS));
  }

  /**
   * On a successful concurrent computation, only one thread does the work, but all the threads get
   * the same result.
   */
  private static void testConcurrentLoadingDefault(CacheBuilder<Object, Object> builder)
      throws InterruptedException {

  }

  @GwtIncompatible // Only used by @GwtIncompatible code
  private abstract static class EmptyIteratorTester extends IteratorTester<Integer> {
    protected EmptyIteratorTester() {
      super(3, MODIFIABLE, Collections.<Integer>emptySet(), IteratorTester.KnownOrder.KNOWN_ORDER);
    }
  }

  @GwtIncompatible // Only used by @GwtIncompatible code

 *
 * <p>This class should be used by other collection classes only.
 *
 * @author Mike Bostock
 * @author Jared Levy
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
/*
 * I have decided not to bother adding @ParametricNullness annotations in this class. Adding them is
 * a lot of busy work, and the annotation matters only when the APIs to be annotated are visible to

  @GwtIncompatible // used only from other GwtIncompatible code
  private static final class BitSetMatcher extends NamedFastMatcher {

    private final BitSet table;

    private BitSetMatcher(BitSet table, String description) {
      super(description);
      if (table.length() + Long.SIZE < table.size()) {
        table = (BitSet) table.clone();
        // If only we could actually call BitSet.trimToSize() ourselves...

   * <p><i>Performance notes:</i> while the power set of a set with size {@code n} is of size {@code
   * 2^n}, its memory usage is only {@code O(n)}. When the power set is constructed, the input set
   * is merely copied. Only as the power set is iterated are the individual subsets created, and
   * these subsets themselves occupy only a small constant amount of memory.
   *
   * @param set the set of elements to construct a power set from