* queue's iterator:
   *
   * <pre>{@code
   * Queue<E> queue = Queues.synchronizedQueue(MinMaxPriorityQueue.<E>create());
   * ...
   * queue.add(element);  // Needn't be in synchronized block
   * ...
   * synchronized (queue) {  // Must synchronize on queue!
   *   Iterator<E> i = queue.iterator(); // Must be in synchronized block
   *   while (i.hasNext()) {
   *     foo(i.next());

     */
    @CheckForNull
    Class<?> loadFinalizer();
  }

  /**
   * Tries to load Finalizer from the system class loader. If Finalizer is in the system class path,
   * we needn't create a separate loader.
   */
  static class SystemLoader implements FinalizerLoader {
    // This is used by the ClassLoader-leak test in FinalizableReferenceQueueTest to disable

     */
    @CheckForNull
    Class<?> loadFinalizer();
  }

  /**
   * Tries to load Finalizer from the system class loader. If Finalizer is in the system class path,
   * we needn't create a separate loader.
   */
  static class SystemLoader implements FinalizerLoader {
    // This is used by the ClassLoader-leak test in FinalizableReferenceQueueTest to disable

      return removal;
    }
  }

  /**
   * Any updates to LocalCache.Strength used in CacheBuilder need to be matched in this class for
   * compilation purposes.
   */
  enum Strength {
    /*
     * TODO(kevinb): If we strongly reference the value and aren't loading, we needn't wrap the
     * value. This could save ~8 bytes per entry.
     */

    STRONG {
      @Override

   * of its collection views:
   *
   * <pre>{@code
   * Table<R, C, V> table = Tables.synchronizedTable(HashBasedTable.<R, C, V>create());
   * ...
   * Map<C, V> row = table.row(rowKey);  // Needn't be in synchronized block
   * ...
   * synchronized (table) {  // Synchronizing on table, not row!
   *   Iterator<Entry<C, V>> i = row.entrySet().iterator(); // Must be in synchronized block
   *   while (i.hasNext()) {

    K key = null;

    Multimap<K, V> multimap = Multimaps.synchronizedMultimap(HashMultimap.<K, V>create());
    Collection<V> values = multimap.get(key); // Needn't be in synchronized block
    synchronized (multimap) { // Synchronizing on multimap, not values!
      Iterator<V> i = values.iterator(); // Must be in synchronized block
      while (i.hasNext()) {

      void genericTestSynchronizedMultimapSampleCodeCompilation() {
    K key = null;

    Multimap<K, V> multimap = Multimaps.synchronizedMultimap(HashMultimap.<K, V>create());
    Collection<V> values = multimap.get(key); // Needn't be in synchronized block
    synchronized (multimap) { // Synchronizing on multimap, not values!
      Iterator<V> i = values.iterator(); // Must be in synchronized block
      while (i.hasNext()) {
        foo(i.next());

   * of its collection views:
   *
   * <pre>{@code
   * BiMap<Long, String> map = Maps.synchronizedBiMap(
   *     HashBiMap.<Long, String>create());
   * ...
   * Set<Long> set = map.keySet();  // Needn't be in synchronized block
   * ...
   * synchronized (map) {  // Synchronizing on map, not set!
   *   Iterator<Long> it = set.iterator(); // Must be in synchronized block
   *   while (it.hasNext()) {

   *
   * <pre>{@code
   * Multimap<K, V> multimap = Multimaps.synchronizedMultimap(
   *     HashMultimap.<K, V>create());
   * ...
   * Collection<V> values = multimap.get(key);  // Needn't be in synchronized block
   * ...
   * synchronized (multimap) {  // Synchronizing on multimap, not values!
   *   Iterator<V> i = values.iterator(); // Must be in synchronized block
   *   while (i.hasNext()) {

     * The key reference queue contains entries whose keys have been garbage collected, and which
     * need to be cleaned up internally.
     */
    @CheckForNull final ReferenceQueue<K> keyReferenceQueue;

    /**
     * The value reference queue contains value references whose values have been garbage collected,
     * and which need to be cleaned up internally.
     */
    @CheckForNull final ReferenceQueue<V> valueReferenceQueue;