}

    @Override
    public void finalizeReferent() {
      finalizeReferentCalled = true;
    }
  }

  /**
   * Keeps a weak reference to the underlying reference queue. When this reference is cleared, we
   * know that the background thread has stopped and released its strong reference.
   */
  private WeakReference<ReferenceQueue<Object>> queueReference;


  public void testThatFinalizerStops() {
    weaklyReferenceQueue();

    if (threadStarted) {
      return;
    }

    Reference<?> reference;
    while ((reference = queue.poll()) != null) {
      /*
       * This is for the benefit of phantom references. Weak and soft references will have already
       * been cleared by this point.
       */
      reference.clear();
      try {
        ((FinalizableReference) reference).finalizeReferent();
      } catch (Throwable t) {

When adding links which point to resources within git repositories, like
KEPs or supporting documentation, please reference a specific commit and avoid
linking directly to the master branch. This ensures that links reference a
specific point in time, rather than a document that may change over time.

        () -> equalsTester.addEqualityGroup(reference, equalObject1, null));
  }

  /** Test adding null equal object yields error */
  public void testAddNullEqualObject() {
    assertThrows(
        NullPointerException.class,
        () -> equalsTester.addEqualityGroup(reference, (Object[]) null));
  }

  /**
   * Test adding objects only by addEqualityGroup, with no reference object specified in the
   * constructor.
   */

    schemas: Optional[Dict[str, Union[Schema, Reference]]] = None
    responses: Optional[Dict[str, Union[Response, Reference]]] = None
    parameters: Optional[Dict[str, Union[Parameter, Reference]]] = None
    examples: Optional[Dict[str, Union[Example, Reference]]] = None
    requestBodies: Optional[Dict[str, Union[RequestBody, Reference]]] = None
    headers: Optional[Dict[str, Union[Header, Reference]]] = None

    if (adjacentNodes != null) {
      checkState(adjacentNodes.add(node));
    }
  }

  @CheckForNull
  private static <T> T getReference(@CheckForNull Reference<T> reference) {
    return (reference == null) ? null : reference.get();
  }

/**
 * An immutable object that may contain a non-null reference to another object. Each instance of
 * this type either contains a non-null reference, or contains nothing (in which case we say that
 * the reference is "absent"); it is never said to "contain {@code null}".
 *
 * <p>A non-null {@code Optional<T>} reference can be used as a replacement for a nullable {@code T}

		nrules[pattern] = nrules[pattern].Union(targetIDSet)
	}

	return nrules
}

// Difference - returns difference with given rules as new rules.
func (rules Rules) Difference(rules2 Rules) Rules {
	nrules := make(Rules)

	for pattern, targetIDSet := range rules {
		if nv := targetIDSet.Difference(rules2[pattern]); len(nv) > 0 {
			nrules[pattern] = nv
		}
	}

	return nrules

    Set<String> enemies = 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>());

    enemies.add("Dave");
    assertEquals(1, goodFriends.size());

		t.Fatal(err)
	}
	isClosed := rlk.IsClosed()
	if isClosed {
		t.Fatal("File ref count shouldn't be zero")
	}

	// Increase reference count to 2.
	rlk.IncLockRef()

	isClosed = rlk.IsClosed()
	if isClosed {
		t.Fatal("File ref count shouldn't be zero")
	}

	// Decrease reference count by 1.
	if err = rlk.Close(); err != nil {
		t.Fatal(err)
	}

	isClosed = rlk.IsClosed()
	if isClosed {