001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.keyvalue;
018
019import java.util.Map;
020
021/**
022 * Abstract Pair class to assist with creating correct
023 * {@link java.util.Map.Entry Map.Entry} implementations.
024 *
025 * @param <K> the type of keys
026 * @param <V> the type of mapped values
027 * @since 3.0
028 */
029public abstract class AbstractMapEntry<K, V> extends AbstractKeyValue<K, V> implements Map.Entry<K, V> {
030
031    /**
032     * Constructs a new entry with the given key and given value.
033     *
034     * @param key  the key for the entry, may be null
035     * @param value  the value for the entry, may be null
036     */
037    protected AbstractMapEntry(final K key, final V value) {
038        super(key, value);
039    }
040
041    /**
042     * Compares this {@code Map.Entry} with another {@code Map.Entry}.
043     * <p>
044     * Implemented per API documentation of {@link java.util.Map.Entry#equals(Object)}
045     *
046     * @param obj  the object to compare to
047     * @return true if equal key and value
048     */
049    @Override
050    public boolean equals(final Object obj) {
051        if (obj == this) {
052            return true;
053        }
054        if (!(obj instanceof Map.Entry)) {
055            return false;
056        }
057        final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
058        return
059            (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey())) &&
060            (getValue() == null ? other.getValue() == null : getValue().equals(other.getValue()));
061    }
062
063    /**
064     * Gets a hashCode compatible with the equals method.
065     * <p>
066     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()}
067     *
068     * @return a suitable hash code
069     */
070    @Override
071    public int hashCode() {
072        return (getKey() == null ? 0 : getKey().hashCode()) ^
073               (getValue() == null ? 0 : getValue().hashCode());
074    }
075
076    /**
077     * Sets the value stored in this {@code Map.Entry}.
078     * <p>
079     * This {@code Map.Entry} is not connected to a Map, so only the
080     * local data is changed.
081     *
082     * @param value  the new value
083     * @return the previous value
084     */
085    @Override
086    public V setValue(final V value) { // NOPMD
087        return super.setValue(value);
088    }
089
090}