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