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 *      http://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.lang3.tuple;
018
019/**
020 * <p>An immutable pair consisting of two {@code Object} elements.</p>
021 *
022 * <p>Although the implementation is immutable, there is no restriction on the objects
023 * that may be stored. If mutable objects are stored in the pair, then the pair
024 * itself effectively becomes mutable. The class is also {@code final}, so a subclass
025 * can not add undesirable behaviour.</p>
026 *
027 * <p>#ThreadSafe# if both paired objects are thread-safe</p>
028 *
029 * @param <L> the left element type
030 * @param <R> the right element type
031 *
032 * @since 3.0
033 */
034public final class ImmutablePair<L, R> extends Pair<L, R> {
035
036    /**
037     * An immutable pair of nulls.
038     */
039    // This is not defined with generics to avoid warnings in call sites.
040    @SuppressWarnings("rawtypes")
041    private static final ImmutablePair NULL = of(null, null);
042
043    /** Serialization version */
044    private static final long serialVersionUID = 4954918890077093841L;
045
046    /**
047     * Returns an immutable pair of nulls.
048     *
049     * @param <L> the left element of this pair. Value is {@code null}.
050     * @param <R> the right element of this pair. Value is {@code null}.
051     * @return an immutable pair of nulls.
052     * @since 3.6
053     */
054    @SuppressWarnings("unchecked")
055    public static <L, R> ImmutablePair<L, R> nullPair() {
056        return NULL;
057    }
058
059    /** Left object */
060    public final L left;
061    /** Right object */
062    public final R right;
063
064    /**
065     * <p>Obtains an immutable pair of two objects inferring the generic types.</p>
066     *
067     * <p>This factory allows the pair to be created using inference to
068     * obtain the generic types.</p>
069     *
070     * @param <L> the left element type
071     * @param <R> the right element type
072     * @param left  the left element, may be null
073     * @param right  the right element, may be null
074     * @return a pair formed from the two parameters, not null
075     */
076    public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
077        return new ImmutablePair<>(left, right);
078    }
079
080    /**
081     * Create a new pair instance.
082     *
083     * @param left  the left value, may be null
084     * @param right  the right value, may be null
085     */
086    public ImmutablePair(final L left, final R right) {
087        super();
088        this.left = left;
089        this.right = right;
090    }
091
092    //-----------------------------------------------------------------------
093    /**
094     * {@inheritDoc}
095     */
096    @Override
097    public L getLeft() {
098        return left;
099    }
100
101    /**
102     * {@inheritDoc}
103     */
104    @Override
105    public R getRight() {
106        return right;
107    }
108
109    /**
110     * <p>Throws {@code UnsupportedOperationException}.</p>
111     *
112     * <p>This pair is immutable, so this operation is not supported.</p>
113     *
114     * @param value  the value to set
115     * @return never
116     * @throws UnsupportedOperationException as this operation is not supported
117     */
118    @Override
119    public R setValue(final R value) {
120        throw new UnsupportedOperationException();
121    }
122
123}