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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;

	/**
	* <p>An immutable pair consisting of two {@code Object} elements.</p>
	*
	* <p>Although the implementation is immutable, there is no restriction on the objects
	* that may be stored. If mutable objects are stored in the pair, then the pair
	* itself effectively becomes mutable. The class is also {@code final}, so a subclass
	* can not add undesirable behavior.</p>
	*
	* <p>#ThreadSafe# if both paired objects are thread-safe</p>
	*
	* @param <L> the left element type
	* @param <R> the right element type
	*
	* @since 3.0
	*/
	public final class ImmutablePair<L, R> extends Pair<L, R> {

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

	/**
	* An immutable pair of nulls.
	*/
	// This is not defined with generics to avoid warnings in call sites.
	@SuppressWarnings("rawtypes")
	private static final ImmutablePair NULL = of(null, null);

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

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

	/**
	* <p>Creates an immutable pair of two objects inferring the generic types.</p>
	*
	* <p>This factory allows the pair to be created using inference to
	* obtain the generic types.</p>
	*
	* @param <L> the left element type
	* @param <R> the right element type
	* @param left the left element, may be null
	* @return a pair formed from the two parameters, not null
	* @since 3.11
	*/
	public static <L, R> Pair<L, R> left(final L left) {
	return ImmutablePair.of(left, null);
	}

	/**
	* Returns an immutable pair of nulls.
	*
	* @param <L> the left element of this pair. Value is {@code null}.
	* @param <R> the right element of this pair. Value is {@code null}.
	* @return an immutable pair of nulls.
	* @since 3.6
	*/
	public static <L, R> ImmutablePair<L, R> nullPair() {
	return NULL;
	}

	/**
	* <p>Creates an immutable pair of two objects inferring the generic types.</p>
	*
	* <p>This factory allows the pair to be created using inference to
	* obtain the generic types.</p>
	*
	* @param <L> the left element type
	* @param <R> 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 <L, R> ImmutablePair<L, R> of(final L left, final R right) {
	return new ImmutablePair<>(left, right);
	}

	/**
	* <p>Creates an immutable pair from an existing pair.</p>
	*
	* <p>This factory allows the pair to be created using inference to
	* obtain the generic types.</p>
	*
	* @param <L> the left element type
	* @param <R> the right element type
	* @param pair the existing pair.
	* @return a pair formed from the two parameters, not null
	* @since 3.10
	*/
	public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
	final L left;
	final R right;
	if (pair != null) {
	left = pair.getKey();
	right = pair.getValue();
	} else {
	left = null;
	right = null;
	}
	return new ImmutablePair<>(left, right);
	}

	/**
	* <p>Creates an immutable pair of two objects inferring the generic types.</p>
	*
	* <p>This factory allows the pair to be created using inference to
	* obtain the generic types.</p>
	*
	* @param <L> the left element type
	* @param <R> the right element type
	* @param right the right element, may be null
	* @return a pair formed from the two parameters, not null
	* @since 3.11
	*/
	public static <L, R> Pair<L, R> right(final R right) {
	return ImmutablePair.of(null, right);
	}

	/** Left object */
	public final L left;

	/** Right object */
	public final R right;

	/**
	* Create a new pair instance.
	*
	* @param left the left value, may be null
	* @param right the right value, may be null
	*/
	public ImmutablePair(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;
	}

	/**
	* <p>Throws {@code UnsupportedOperationException}.</p>
	*
	* <p>This pair is immutable, so this operation is not supported.</p>
	*
	* @param value the value to set
	* @return never
	* @throws UnsupportedOperationException as this operation is not supported
	*/
	@Override
	public R setValue(final R value) {
	throw new UnsupportedOperationException();
	}

	}

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