Set<String> friends = Sets.newHashSet("Tom", "Joe", "Dave");
    Set<String> enemies = Sets.newHashSet("Dick", "Harry", "Tom");

    Set<String> goodFriends = Sets.difference(friends, enemies);
    assertEquals(2, goodFriends.size());

    ImmutableSet<String> immut = Sets.difference(friends, enemies).immutableCopy();
    HashSet<String> mut = Sets.difference(friends, enemies).copyInto(new HashSet<String>());

    Set<String> friends = Sets.newHashSet("Tom", "Joe", "Dave");
    Set<String> enemies = Sets.newHashSet("Dick", "Harry", "Tom");

    Set<String> goodFriends = Sets.difference(friends, enemies);
    assertEquals(2, goodFriends.size());

    ImmutableSet<String> immut = Sets.difference(friends, enemies).immutableCopy();
    HashSet<String> mut = Sets.difference(friends, enemies).copyInto(new HashSet<String>());

            <!-- Even after we stop using JSR305 annotations in our own code, we'll want this link so that NullPointerTester's docs can link to @CheckForNull and friends... at least once we start using this config for guava-testlib. -->
            <offlineLink>
              <url>https://static.javadoc.io/com.google.code.findbugs/jsr305/3.0.1/</url>

    resetContainer();
  }

  /**
   * @return the contents of the container under test, for use by {@link #expectContents(Object[])
   *     expectContents(E...)} and its friends.
   */
  protected abstract Collection<E> actualContents();

  /**
   * Replaces the existing container under test with a new container created by the subject
   * generator.
   *

            <!-- Even after we stop using JSR305 annotations in our own code, we'll want this link so that NullPointerTester's docs can link to @CheckForNull and friends... at least once we start using this config for guava-testlib. -->
            <offlineLink>
              <url>https://static.javadoc.io/com.google.code.findbugs/jsr305/3.0.1/</url>

    resetContainer();
  }

  /**
   * @return the contents of the container under test, for use by {@link #expectContents(Object[])
   *     expectContents(E...)} and its friends.
   */
  protected abstract Collection<E> actualContents();

  /**
   * Replaces the existing container under test with a new container created by the subject
   * generator.
   *

    @CheckForNull ValueEntry<K, V> nextInValueBucket;
    /*
     * The *InValueSet and *InMultimap fields below are null after construction, but we almost
     * always call succeedsIn*() to initialize them immediately thereafter.
     *
     * The exception is the *InValueSet fields of multimapHeaderEntry, which are never set. (That

    extends AggregateFuture<V, C> {
  /*
   * We access this field racily but safely. For discussion of a similar situation, see the comments
   * on the fields of TimeoutFuture. This field is slightly different from the fields discussed
   * there: cancel() never reads this field, only writes to it. That makes the race here completely
   * harmless, rather than just 99.99% harmless.
   */

     * we can reference a node whose fields have been cleared is inside the iterator (and presumably
     * only under concurrent modification).
     *
     * To access these fields when you know that they are not null, call the pred() and succ()
     * methods, which perform null checks before returning the fields.
     */
    @CheckForNull private AvlNode<E> pred;

  }

  private static final int ENDPOINT = -2;

  // TODO(user): predecessors and successors should be collocated (reducing cache misses).
  // Might also explore collocating all of [hash, next, predecessor, successor] fields of an
  // entry in a *single* long[], though that reduces the maximum size of the set by a factor of 2

  /**
   * Pointer to the predecessor of an entry in insertion order. ENDPOINT indicates a node is the