*     Object} if any key is acceptable
 * @author Charles Fry
 * @since 10.0
 */
@GwtCompatible
@FunctionalInterface
@ElementTypesAreNonnullByDefault
public interface RemovalListener<K, V> {
  /**
   * Notifies the listener that a removal occurred at some point in the past.
   *
   * <p>This does not always signify that the key is now absent from the cache, as it may have
   * already been re-added.

 *     Object} if any key is acceptable
 * @author Charles Fry
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface RemovalListener<K, V> {
  /**
   * Notifies the listener that a removal occurred at some point in the past.
   *
   * <p>This does not always signify that the key is now absent from the cache, as it may have
   * already been re-added.

@ElementTypesAreNonnullByDefault
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(

@ElementTypesAreNonnullByDefault
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(

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Utility {@link RemovalListener} implementations intended for use in testing.
 *
 * @author mike nonemacher
 */
@GwtCompatible(emulated = true)
class TestingRemovalListeners {

  /** Returns a new no-op {@code RemovalListener}. */
  static <K, V> NullRemovalListener<K, V> nullRemovalListener() {
    return new NullRemovalListener<>();
  }

    }
  }

  public void testRemovalListener_setTwice() {
    RemovalListener<Object, Object> testListener = nullRemovalListener();
    CacheBuilder<Object, Object> builder = CacheBuilder.newBuilder().removalListener(testListener);
    try {
      // even to the same instance is not allowed
      builder = builder.removalListener(testListener);
      fail();
    } catch (IllegalStateException expected) {
    }

            .removalListener(removalListener)
            .ticker(ticker)
            .build(loader);
    runRemovalScheduler(cache, removalListener, loader, ticker, KEY_PREFIX, EXPIRING_TIME);
  }

  public void testRemovalScheduler_expireAfterBoth() {
    FakeTicker ticker = new FakeTicker();
    CountingRemovalListener<String, Integer> removalListener = countingRemovalListener();

  }

  public void testGet() {
    Object computed = new Object();
    LoadingCache<Object, Object> cache =
        CacheBuilder.newBuilder()
            .maximumSize(0)
            .removalListener(listener)
            .build(constantLoader(computed));

    Object key = new Object();
    assertSame(computed, cache.getUnchecked(key));
    RemovalNotification<Object, Object> notification = listener.remove();

  }

  public void testEviction_maxSize() {
    CountingRemovalListener<Integer, Integer> removalListener = countingRemovalListener();
    IdentityLoader<Integer> loader = identityLoader();
    LoadingCache<Integer, Integer> cache =
        CacheBuilder.newBuilder()
            .maximumSize(MAX_SIZE)
            .removalListener(removalListener)
            .build(loader);
    for (int i = 0; i < 2 * MAX_SIZE; i++) {

    }
  }

  public void testRemovalListener_setTwice() {
    RemovalListener<Object, Object> testListener = nullRemovalListener();
    CacheBuilder<Object, Object> builder = CacheBuilder.newBuilder().removalListener(testListener);
    try {
      // even to the same instance is not allowed
      builder = builder.removalListener(testListener);
      fail();
    } catch (IllegalStateException expected) {
    }