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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4.keyvalue;

import java.util.Map;

/**
 * Abstract Pair class to assist with creating correct
 * {@link java.util.Map.Entry Map.Entry} implementations.
 *
 * @since 3.0
 */
public abstract class AbstractMapEntry extends AbstractKeyValue implements Map.Entry {

    /**
     * Constructs a new entry with the given key and given value.
     *
     * @param key  the key for the entry, may be null
     * @param value  the value for the entry, may be null
     */
    protected AbstractMapEntry(final K key, final V value) {
        super(key, value);
    }

    // Map.Entry interface
    //-------------------------------------------------------------------------
    /**
     * Sets the value stored in this Map.Entry.
     * 
     * This Map.Entry is not connected to a Map, so only the
     * local data is changed.
     *
     * @param value  the new value
     * @return the previous value
     */
    @Override
    public V setValue(final V value) { // NOPMD
        return super.setValue(value);
    }

    /**
     * Compares this Map.Entry with another Map.Entry.
     * 

     * Implemented per API documentation of {@link java.util.Map.Entry#equals(Object)}
     *
     * @param obj  the object to compare to
     * @return true if equal key and value
     */
    @Override
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof Map.Entry == false) {
            return false;
        }
        final Map.Entry other = (Map.Entry) obj;
        return
            (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey())) &&
            (getValue() == null ? other.getValue() == null : getValue().equals(other.getValue()));
    }

    /**
     * Gets a hashCode compatible with the equals method.
     * 
     * Implemented per API documentation of {@link java.util.Map.Entry#hashCode()}
     *
     * @return a suitable hash code
     */
    @Override
    public int hashCode() {
        return (getKey() == null ? 0 : getKey().hashCode()) ^
               (getValue() == null ? 0 : getValue().hashCode());
    }

}