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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. Guava has only one code dependency - javax.annotation, per the JSR-305 spec.

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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.cache;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;

import java.util.Map.Entry;

import javax.annotation.Nullable;

/**
 * A notification of the removal of a single entry. The key and/or value may be null if they were
 * already garbage collected.
 *
 * Like other {@code Map.Entry} instances associated with {@code CacheBuilder}, this class holds
 * strong references to the key and value, regardless of the type of references the cache may be
 * using.
 *
 * @author Charles Fry
 * @since 10.0
 */
@GwtCompatible
public final class RemovalNotification implements Entry {
  @Nullable private final K key;
  @Nullable private final V value;
  private final RemovalCause cause;

  /**
   * Creates a new {@code RemovalNotification} for the given {@code key}/{@code value} pair, with
   * the given {@code cause} for the removal. The {@code key} and/or {@code value} may be
   * {@code null} if they were already garbage collected.
   *
   * @since 19.0
   */
  public static  RemovalNotification create(
      @Nullable K key, @Nullable V value, RemovalCause cause) {
    return new RemovalNotification(key, value, cause);
  }

  private RemovalNotification(@Nullable K key, @Nullable V value, RemovalCause cause) {
    this.key = key;
    this.value = value;
    this.cause = checkNotNull(cause);
  }

  /**
   * Returns the cause for which the entry was removed.
   */
  public RemovalCause getCause() {
    return cause;
  }

  /**
   * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
   * {@link RemovalCause#EXPLICIT} nor {@link RemovalCause#REPLACED}).
   */
  public boolean wasEvicted() {
    return cause.wasEvicted();
  }

  @Nullable @Override public K getKey() {
    return key;
  }

  @Nullable @Override public V getValue() {
    return value;
  }

  @Override public final V setValue(V value) {
    throw new UnsupportedOperationException();
  }

  @Override public boolean equals(@Nullable Object object) {
    if (object instanceof Entry) {
      Entry that = (Entry) object;
      return Objects.equal(this.getKey(), that.getKey())
          && Objects.equal(this.getValue(), that.getValue());
    }
    return false;
  }

  @Override public int hashCode() {
    K k = getKey();
    V v = getValue();
    return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
  }

  /**
   * Returns a string representation of the form {key}={value}.
   */
  @Override public String toString() {
    return getKey() + "=" + getValue();
  }
  private static final long serialVersionUID = 0;
}