public final class RemovalListeners {

  private RemovalListeners() {}

  /**
   * Returns a {@code RemovalListener} which processes all eviction notifications using {@code
   * executor}.
   *
   * @param listener the backing listener
   * @param executor the executor with which removal notifications are asynchronously executed
   */
  public static <K, V> RemovalListener<K, V> asynchronous(

    // other operations, the cache and the removal queue won't change from this point on.

    // Verify that each received removal notification was valid
    for (RemovalNotification<String, String> notification : removalListener) {
      assertEquals("Invalid removal notification", notification.getKey(), notification.getValue());
    }

    CacheStats stats = cache.stats();
    assertEquals(removalListener.size(), stats.evictionCount());

    // other operations, the cache and the removal queue won't change from this point on.

    // Verify that each received removal notification was valid
    for (RemovalNotification<String, String> notification : removalListener) {
      assertEquals("Invalid removal notification", notification.getKey(), notification.getValue());
    }

    CacheStats stats = cache.stats();
    assertEquals(removalListener.size(), stats.evictionCount());

    /** The key of the message: Last Access Time */
    public static final String LABELS_LAST_ACCESS_TIME = "{labels.lastAccessTime}";

    /** The key of the message: Notification To */
    public static final String LABELS_NOTIFICATION_TO = "{labels.notificationTo}";

    /** The key of the message: Num */
    public static final String LABELS_NUM = "{labels.num}";

    /** The key of the message: Page Number */

    assertEquals("Map must be empty by now", 0, cache.size());
    assertEquals("Eviction notifications must be received", 10, removalListener.getCount());

    CacheTesting.expireEntries((LoadingCache<?, ?>) cache, EXPIRING_TIME, ticker);
    // ensure that no new notifications are sent
    assertEquals("Eviction notifications must be received", 10, removalListener.getCount());
  }

      QueuingRemovalListener<K, V> listener, K key, V value, RemovalCause cause) {
    RemovalNotification<K, V> notification = listener.remove();
    assertSame(key, notification.getKey());
    assertSame(value, notification.getValue());
    assertSame(cause, notification.getCause());
  }

  // Segment core tests

  public void testNewEntry() {

    // Notification Configuration
    // ============================================================

    /** Notification configuration for login page. */
    public static final String NOTIFICATION_LOGIN = "notification.login";

    /** Notification configuration for search top page. */
    public static final String NOTIFICATION_SEARCH_TOP = "notification.search.top";

    Object key = new Object();
    assertSame(computed, cache.getUnchecked(key));
    RemovalNotification<Object, Object> notification = listener.remove();
    assertSame(key, notification.getKey());
    assertSame(computed, notification.getValue());
    assertSame(RemovalCause.SIZE, notification.getCause());
    assertTrue(listener.isEmpty());
    checkEmpty(cache);
  }

  public void testGet_expireAfterWrite() {

    Object key = new Object();
    assertSame(computed, cache.getUnchecked(key));
    RemovalNotification<Object, Object> notification = listener.remove();
    assertSame(key, notification.getKey());
    assertSame(computed, notification.getValue());
    assertSame(RemovalCause.SIZE, notification.getCause());
    assertTrue(listener.isEmpty());
    checkEmpty(cache);
  }

  public void testGet_expireAfterWrite() {

  static class QueuingRemovalListener<K, V> extends ConcurrentLinkedQueue<RemovalNotification<K, V>>
      implements RemovalListener<K, V> {

    @Override
    public void onRemoval(RemovalNotification<K, V> notification) {
      add(notification);
    }
  }

  /**
   * {@link RemovalListener} that counts each {@link RemovalNotification} it receives, and provides
   * access to the most-recently received one.
   */