com.google.common.cache.RemovalNotification.java Source code

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Here is the source code for com.google.common.cache.RemovalNotification.java

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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.
 *
 * <p>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<K, V> implements Entry<K, V> {
    @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 <K, V> RemovalNotification<K, V> 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 <code>{key}={value}</code>.
     */
    @Override
    public String toString() {
        return getKey() + "=" + getValue();
    }

    private static final long serialVersionUID = 0;
}