    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
    021import org.apache.commons.collections4.KeyValue;
    022
    023/**
    024 * A mutable <code>KeyValue</code> pair that does not implement
    025 * {@link java.util.Map.Entry Map.Entry}.
    026 * <p>
    027 * Note that a <code>DefaultKeyValue</code> instance may not contain
    028 * itself as a key or value.
    029 *
    030 * @since 3.0
    031 */
    032public class DefaultKeyValue<K, V> extends AbstractKeyValue<K, V> {
    033
    034    /**
    035     * Constructs a new pair with a null key and null value.
    036     */
    037    public DefaultKeyValue() {
    038        super(null, null);
    039    }
    040
    041    /**
    042     * Constructs a new pair with the specified key and given value.
    043     *
    044     * @param key  the key for the entry, may be null
    045     * @param value  the value for the entry, may be null
    046     */
    047    public DefaultKeyValue(final K key, final V value) {
    048        super(key, value);
    049    }
    050
    051    /**
    052     * Constructs a new pair from the specified <code>KeyValue</code>.
    053     *
    054     * @param pair  the pair to copy, must not be null
    055     * @throws NullPointerException if the entry is null
    056     */
    057    public DefaultKeyValue(final KeyValue<? extends K, ? extends V> pair) {
    058        super(pair.getKey(), pair.getValue());
    059    }
    060
    061    /**
    062     * Constructs a new pair from the specified <code>Map.Entry</code>.
    063     *
    064     * @param entry  the entry to copy, must not be null
    065     * @throws NullPointerException if the entry is null
    066     */
    067    public DefaultKeyValue(final Map.Entry<? extends K, ? extends V> entry) {
    068        super(entry.getKey(), entry.getValue());
    069    }
    070
    071    //-----------------------------------------------------------------------
    072    /**
    073     * Sets the key.
    074     *
    075     * @param key  the new key
    076     * @return the old key
    077     * @throws IllegalArgumentException if key is this object
    078     */
    079    @Override
    080    public K setKey(final K key) {
    081        if (key == this) {
    082            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a key.");
    083        }
    084
    085        return super.setKey(key);
    086    }
    087
    088    /**
    089     * Sets the value.
    090     *
    091     * @return the old value of the value
    092     * @param value the new value
    093     * @throws IllegalArgumentException if value is this object
    094     */
    095    @Override
    096    public V setValue(final V value) {
    097        if (value == this) {
    098            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a value.");
    099        }
    100
    101        return super.setValue(value);
    102    }
    103
    104    //-----------------------------------------------------------------------
    105    /**
    106     * Returns a new <code>Map.Entry</code> object with key and value from this pair.
    107     *
    108     * @return a MapEntry instance
    109     */
    110    public Map.Entry<K, V> toMapEntry() {
    111        return new DefaultMapEntry<>(this);
    112    }
    113
    114    //-----------------------------------------------------------------------
    115    /**
    116     * Compares this <code>Map.Entry</code> with another <code>Map.Entry</code>.
    117     * <p>
    118     * Returns true if the compared object is also a <code>DefaultKeyValue</code>,
    119     * and its key and value are equal to this object's key and value.
    120     *
    121     * @param obj  the object to compare to
    122     * @return true if equal key and value
    123     */
    124    @Override
    125    public boolean equals(final Object obj) {
    126        if (obj == this) {
    127            return true;
    128        }
    129        if (obj instanceof DefaultKeyValue == false) {
    130            return false;
    131        }
    132
    133        final DefaultKeyValue<?, ?> other = (DefaultKeyValue<?, ?>) obj;
    134        return
    135            (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey())) &&
    136            (getValue() == null ? other.getValue() == null : getValue().equals(other.getValue()));
    137    }
    138
    139    /**
    140     * Gets a hashCode compatible with the equals method.
    141     * <p>
    142     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()},
    143     * however subclasses may override this.
    144     *
    145     * @return a suitable hash code
    146     */
    147    @Override
    148    public int hashCode() {
    149        return (getKey() == null ? 0 : getKey().hashCode()) ^
    150               (getValue() == null ? 0 : getValue().hashCode());
    151    }
    152
    153}