    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 *      https://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;
    020import java.util.Map.Entry;
    021import java.util.Objects;
    022
    023import org.apache.commons.collections4.KeyValue;
    024
    025/**
    026 * A mutable {@code KeyValue} pair that does not implement
    027 * {@link Entry Map.Entry}.
    028 * <p>
    029 * Note that a {@code DefaultKeyValue} instance may not contain
    030 * itself as a key or value.
    031 * </p>
    032 *
    033 * @param <K> The type of keys
    034 * @param <V> The type of values
    035 * @since 3.0
    036 */
    037public class DefaultKeyValue<K, V> extends AbstractKeyValue<K, V> {
    038
    039    /**
    040     * Constructs a new pair with a null key and null value.
    041     */
    042    public DefaultKeyValue() {
    043        super(null, null);
    044    }
    045
    046    /**
    047     * Constructs a new pair with the specified key and given value.
    048     *
    049     * @param key  The key for the entry, may be null
    050     * @param value  The value for the entry, may be null
    051     */
    052    public DefaultKeyValue(final K key, final V value) {
    053        super(key, value);
    054    }
    055
    056    /**
    057     * Constructs a new pair from the specified {@code KeyValue}.
    058     *
    059     * @param pair  The pair to copy, must not be null
    060     * @throws NullPointerException if the entry is null
    061     */
    062    public DefaultKeyValue(final KeyValue<? extends K, ? extends V> pair) {
    063        super(pair.getKey(), pair.getValue());
    064    }
    065
    066    /**
    067     * Constructs a new pair from the specified {@code Map.Entry}.
    068     *
    069     * @param entry  The entry to copy, must not be null
    070     * @throws NullPointerException if the entry is null
    071     */
    072    public DefaultKeyValue(final Map.Entry<? extends K, ? extends V> entry) {
    073        super(entry.getKey(), entry.getValue());
    074    }
    075
    076    /**
    077     * Compares this {@code Map.Entry} with another {@code Map.Entry}.
    078     * <p>
    079     * Returns true if the compared object is also a {@code DefaultKeyValue},
    080     * and its key and value are equal to this object's key and value.
    081     *
    082     * @param obj  The object to compare to
    083     * @return true if equal key and value
    084     */
    085    @Override
    086    public boolean equals(final Object obj) {
    087        if (obj == this) {
    088            return true;
    089        }
    090        if (!(obj instanceof DefaultKeyValue)) {
    091            return false;
    092        }
    093
    094        final DefaultKeyValue<?, ?> other = (DefaultKeyValue<?, ?>) obj;
    095        return
    096            Objects.equals(getKey(), other.getKey()) &&
    097            Objects.equals(getValue(), other.getValue());
    098    }
    099
    100    /**
    101     * Gets a hashCode compatible with the equals method.
    102     * <p>
    103     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()},
    104     * however subclasses may override this.
    105     *
    106     * @return A suitable hash code
    107     */
    108    @Override
    109    public int hashCode() {
    110        return (getKey() == null ? 0 : getKey().hashCode()) ^
    111               (getValue() == null ? 0 : getValue().hashCode());
    112    }
    113
    114    /**
    115     * Sets the key.
    116     *
    117     * @param key  The new key
    118     * @return The old key
    119     * @throws IllegalArgumentException if key is this object
    120     */
    121    @Override
    122    public K setKey(final K key) {
    123        if (key == this) {
    124            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a key.");
    125        }
    126
    127        return super.setKey(key);
    128    }
    129
    130    /**
    131     * Sets the value.
    132     *
    133     * @return The old value of the value
    134     * @param value The new value
    135     * @throws IllegalArgumentException if value is this object
    136     */
    137    @Override
    138    public V setValue(final V value) {
    139        if (value == this) {
    140            throw new IllegalArgumentException("DefaultKeyValue may not contain itself as a value.");
    141        }
    142
    143        return super.setValue(value);
    144    }
    145
    146    /**
    147     * Returns a new {@code Map.Entry} object with key and value from this pair.
    148     *
    149     * @return A MapEntry instance
    150     */
    151    public Map.Entry<K, V> toMapEntry() {
    152        return new DefaultMapEntry<>(this);
    153    }
    154
    155}