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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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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.lang3.tuple;

import java.util.Map;

/**
 * A mutable pair consisting of two {@code Object} elements.
 *
 * Not #ThreadSafe#
 *
 * @param  the left element type
 * @param  the right element type
 *
 * @since 3.0
 */
public class MutablePair extends Pair {

    /**
     * An empty array.
     * 
     * Consider using {@link #emptyArray()} to avoid generics warnings.
     * 
     *
     * @since 3.10.
     */
    public static final MutablePair[] EMPTY_ARRAY = new MutablePair[0];

    /** Serialization version */
    private static final long serialVersionUID = 4954918890077093841L;

    /**
     * Returns the empty array singleton that can be assigned without compiler warning.
     *
     * @param  the left element type
     * @param  the right element type
     * @return the empty array singleton that can be assigned without compiler warning.
     *
     * @since 3.10.
     */
    @SuppressWarnings("unchecked")
    public static  MutablePair[] emptyArray() {
        return (MutablePair[]) EMPTY_ARRAY;
    }

    /**
     * Creates a mutable pair of two objects inferring the generic types.
     *
     * This factory allows the pair to be created using inference to
     * obtain the generic types.
     *
     * @param  the left element type
     * @param  the right element type
     * @param left  the left element, may be null
     * @param right  the right element, may be null
     * @return a pair formed from the two parameters, not null
     */
    public static  MutablePair of(final L left, final R right) {
        return new MutablePair<>(left, right);
    }

    /**
     * Creates a mutable pair from an existing pair.
     *
     * This factory allows the pair to be created using inference to
     * obtain the generic types.
     *
     * @param  the left element type
     * @param  the right element type
     * @param pair the existing pair.
     * @return a pair formed from the two parameters, not null
     */
    public static  MutablePair of(final Map.Entry pair) {
        final L left;
        final R right;
        if (pair != null) {
            left = pair.getKey();
            right = pair.getValue();
        } else {
            left = null;
            right = null;
        }
        return new MutablePair<>(left, right);
    }

    /** Left object */
    public L left;

    /** Right object */
    public R right;

    /**
     * Create a new pair instance of two nulls.
     */
    public MutablePair() {
        super();
    }

    /**
     * Create a new pair instance.
     *
     * @param left  the left value, may be null
     * @param right  the right value, may be null
     */
    public MutablePair(final L left, final R right) {
        super();
        this.left = left;
        this.right = right;
    }

    //-----------------------------------------------------------------------
    /**
     * {@inheritDoc}
     */
    @Override
    public L getLeft() {
        return left;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public R getRight() {
        return right;
    }

    /**
     * Sets the left element of the pair.
     *
     * @param left  the new value of the left element, may be null
     */
    public void setLeft(final L left) {
        this.left = left;
    }

    /**
     * Sets the right element of the pair.
     *
     * @param right  the new value of the right element, may be null
     */
    public void setRight(final R right) {
        this.right = right;
    }

    /**
     * Sets the {@code Map.Entry} value.
     * This sets the right element of the pair.
     *
     * @param value  the right value to set, not null
     * @return the old value for the right element
     */
    @Override
    public R setValue(final R value) {
        final R result = getRight();
        setRight(value);
        return result;
    }

}