/*

 * 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 org.apache.commons.collections4.KeyValue;

/**

 * Abstract pair class to assist with creating <code>KeyValue</code>

 * and {@link java.util.Map.Entry Map.Entry} implementations.

 *

 * @param <K> the type of keys

 * @param <V> the type of values

 * @since 3.0

 */

public abstract class AbstractKeyValue<K, V> implements KeyValue<K, V> {

    /** The key */

    private K key;

    /** The value */

    private V value;

    /**

     * Constructs a new pair with the specified 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 AbstractKeyValue(final K key, final V value) {

        super();

        this.key = key;

        this.value = value;

    }

    /**

     * Gets the key from the pair.

     *

     * @return the key

     */

    @Override

    public K getKey() {

        return key;

    }

    protected K setKey(final K key) {

        final K old = this.key;

        this.key = key;

        return old;

    }

    /**

     * Gets the value from the pair.

     *

     * @return the value

     */

    @Override

    public V getValue() {

        return value;

    }

    protected V setValue(final V value) {

        final V old = this.value;

        this.value = value;

        return old;

    }

    /**

     * Gets a debugging String view of the pair.

     *

     * @return a String view of the entry

     */

    @Override

    public String toString() {

        return new StringBuilder()

            .append(getKey())

            .append('=')

            .append(getValue())

            .toString();

    }

}