    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.io.Serializable;
    020import java.util.Map;
    021
    022import org.apache.commons.collections4.KeyValue;
    023
    024/**
    025 * A {@link java.util.Map.Entry Map.Entry} tied to a map underneath.
    026 * <p>
    027 * This can be used to enable a map entry to make changes on the underlying
    028 * map, however this will probably mess up any iterators.
    029 * </p>
    030 *
    031 * @param <K> the type of keys
    032 * @param <V> the type of mapped values
    033 * @since 3.0
    034 */
    035public class TiedMapEntry<K, V> implements Map.Entry<K, V>, KeyValue<K, V>, Serializable {
    036
    037    /** Serialization version */
    038    private static final long serialVersionUID = -8453869361373831205L;
    039
    040    /** The map underlying the entry/iterator */
    041    private final Map<K, V> map;
    042
    043    /** The key */
    044    private final K key;
    045
    046    /**
    047     * Constructs a new entry with the given Map and key.
    048     *
    049     * @param map  the map
    050     * @param key  the key
    051     */
    052    public TiedMapEntry(final Map<K, V> map, final K key) {
    053        super();
    054        this.map = map;
    055        this.key = key;
    056    }
    057
    058    // Map.Entry interface
    059    //-------------------------------------------------------------------------
    060    /**
    061     * Gets the key of this entry
    062     *
    063     * @return the key
    064     */
    065    @Override
    066    public K getKey() {
    067        return key;
    068    }
    069
    070    /**
    071     * Gets the value of this entry direct from the map.
    072     *
    073     * @return the value
    074     */
    075    @Override
    076    public V getValue() {
    077        return map.get(key);
    078    }
    079
    080    /**
    081     * Sets the value associated with the key direct onto the map.
    082     *
    083     * @param value  the new value
    084     * @return the old value
    085     * @throws IllegalArgumentException if the value is set to this map entry
    086     */
    087    @Override
    088    public V setValue(final V value) {
    089        if (value == this) {
    090            throw new IllegalArgumentException("Cannot set value to this map entry");
    091        }
    092        return map.put(key, value);
    093    }
    094
    095    /**
    096     * Compares this <code>Map.Entry</code> with another <code>Map.Entry</code>.
    097     * <p>
    098     * Implemented per API documentation of {@link java.util.Map.Entry#equals(Object)}
    099     *
    100     * @param obj  the object to compare to
    101     * @return true if equal key and value
    102     */
    103    @Override
    104    public boolean equals(final Object obj) {
    105        if (obj == this) {
    106            return true;
    107        }
    108        if (obj instanceof Map.Entry == false) {
    109            return false;
    110        }
    111        final Map.Entry<?,?> other = (Map.Entry<?,?>) obj;
    112        final Object value = getValue();
    113        return
    114            (key == null ? other.getKey() == null : key.equals(other.getKey())) &&
    115            (value == null ? other.getValue() == null : value.equals(other.getValue()));
    116    }
    117
    118    /**
    119     * Gets a hashCode compatible with the equals method.
    120     * <p>
    121     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()}
    122     *
    123     * @return a suitable hash code
    124     */
    125    @Override
    126    public int hashCode() {
    127        final Object value = getValue();
    128        return (getKey() == null ? 0 : getKey().hashCode()) ^
    129               (value == null ? 0 : value.hashCode());
    130    }
    131
    132    /**
    133     * Gets a string version of the entry.
    134     *
    135     * @return entry as a string
    136     */
    137    @Override
    138    public String toString() {
    139        return getKey() + "=" + getValue();
    140    }
    141
    142}