001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.cache;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.base.Objects;
023
024import java.util.Map.Entry;
025
026import javax.annotation.Nullable;
027
028/**
029 * A notification of the removal of a single entry. The key and/or value may be null if they were
030 * already garbage collected.
031 *
032 * <p>Like other {@code Map.Entry} instances associated with {@code CacheBuilder}, this class holds
033 * strong references to the key and value, regardless of the type of references the cache may be
034 * using.
035 *
036 * @author Charles Fry
037 * @since 10.0
038 */
039@GwtCompatible
040public final class RemovalNotification<K, V> implements Entry<K, V> {
041  @Nullable private final K key;
042  @Nullable private final V value;
043  private final RemovalCause cause;
044
045  /**
046   * Creates a new {@code RemovalNotification} for the given {@code key}/{@code value} pair, with
047   * the given {@code cause} for the removal. The {@code key} and/or {@code value} may be
048   * {@code null} if they were already garbage collected.
049   *
050   * @since 19.0
051   */
052  public static <K, V> RemovalNotification<K, V> create(
053      @Nullable K key, @Nullable V value, RemovalCause cause) {
054    return new RemovalNotification(key, value, cause);
055  }
056
057  private RemovalNotification(@Nullable K key, @Nullable V value, RemovalCause cause) {
058    this.key = key;
059    this.value = value;
060    this.cause = checkNotNull(cause);
061  }
062
063  /**
064   * Returns the cause for which the entry was removed.
065   */
066  public RemovalCause getCause() {
067    return cause;
068  }
069
070  /**
071   * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
072   * {@link RemovalCause#EXPLICIT} nor {@link RemovalCause#REPLACED}).
073   */
074  public boolean wasEvicted() {
075    return cause.wasEvicted();
076  }
077
078  @Nullable @Override public K getKey() {
079    return key;
080  }
081
082  @Nullable @Override public V getValue() {
083    return value;
084  }
085
086  @Override public final V setValue(V value) {
087    throw new UnsupportedOperationException();
088  }
089
090  @Override public boolean equals(@Nullable Object object) {
091    if (object instanceof Entry) {
092      Entry<?, ?> that = (Entry<?, ?>) object;
093      return Objects.equal(this.getKey(), that.getKey())
094          && Objects.equal(this.getValue(), that.getValue());
095    }
096    return false;
097  }
098
099  @Override public int hashCode() {
100    K k = getKey();
101    V v = getValue();
102    return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
103  }
104
105  /**
106   * Returns a string representation of the form <code>{key}={value}</code>.
107   */
108  @Override public String toString() {
109    return getKey() + "=" + getValue();
110  }
111  private static final long serialVersionUID = 0;
112}