    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 *      https://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
    019import java.util.Map;
    020import java.util.Objects;
    021
    022/**
    023 * An immutable pair consisting of two {@link Object} elements.
    024 *
    025 * <p>Although the implementation is immutable, there is no restriction on the objects
    026 * that may be stored. If mutable objects are stored in the pair, then the pair
    027 * itself effectively becomes mutable.</p>
    028 *
    029 * <p>#ThreadSafe# if both paired objects are thread-safe</p>
    030 *
    031 * @param <L> the left element type
    032 * @param <R> the right element type
    033 * @since 3.0
    034 */
    035public class ImmutablePair<L, R> extends Pair<L, R> {
    036
    037    /**
    038     * An empty array.
    039     * <p>
    040     * Consider using {@link #emptyArray()} to avoid generics warnings.
    041     * </p>
    042     *
    043     * @since 3.10
    044     */
    045    public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = {};
    046
    047    /**
    048     * An immutable pair of nulls.
    049     */
    050    // This is not defined with generics to avoid warnings in call sites.
    051    @SuppressWarnings("rawtypes")
    052    private static final ImmutablePair NULL = new ImmutablePair<>(null, null);
    053
    054    /** Serialization version */
    055    private static final long serialVersionUID = 4954918890077093841L;
    056
    057    /**
    058     * Returns the empty array singleton that can be assigned without compiler warning.
    059     *
    060     * @param <L> the left element type
    061     * @param <R> the right element type
    062     * @return the empty array singleton that can be assigned without compiler warning.
    063     * @since 3.10
    064     */
    065    @SuppressWarnings("unchecked")
    066    public static <L, R> ImmutablePair<L, R>[] emptyArray() {
    067        return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
    068    }
    069
    070    /**
    071     * Creates an immutable pair of two objects inferring the generic types.
    072     *
    073     * <p>This factory allows the pair to be created using inference to
    074     * obtain the generic types.</p>
    075     *
    076     * @param <L> the left element type
    077     * @param <R> the right element type
    078     * @param left  the left element, may be null
    079     * @return a pair formed from the two parameters, not null
    080     * @since 3.11
    081     */
    082    public static <L, R> Pair<L, R> left(final L left) {
    083        return of(left, null);
    084    }
    085
    086    /**
    087     * Returns an immutable pair of nulls.
    088     *
    089     * @param <L> the left element of this pair. Value is {@code null}.
    090     * @param <R> the right element of this pair. Value is {@code null}.
    091     * @return an immutable pair of nulls.
    092     * @since 3.6
    093     */
    094    @SuppressWarnings("unchecked")
    095    public static <L, R> ImmutablePair<L, R> nullPair() {
    096        return NULL;
    097    }
    098
    099    /**
    100     * Creates an immutable pair of two objects inferring the generic types.
    101     *
    102     * <p>This factory allows the pair to be created using inference to
    103     * obtain the generic types.</p>
    104     *
    105     * @param <L> the left element type
    106     * @param <R> the right element type
    107     * @param left  the left element, may be null
    108     * @param right  the right element, may be null
    109     * @return a pair formed from the two parameters, not null
    110     */
    111    public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
    112        return left != null || right != null ? new ImmutablePair<>(left, right) : nullPair();
    113    }
    114
    115    /**
    116     * Creates an immutable pair from a map entry.
    117     *
    118     * <p>This factory allows the pair to be created using inference to
    119     * obtain the generic types.</p>
    120     *
    121     * @param <L> the left element type
    122     * @param <R> the right element type
    123     * @param pair the existing map entry.
    124     * @return a pair formed from the map entry
    125     * @since 3.10
    126     */
    127    public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
    128        return pair != null ? new ImmutablePair<>(pair.getKey(), pair.getValue()) : nullPair();
    129    }
    130
    131    /**
    132     * Creates an immutable pair of two non-null objects inferring the generic types.
    133     *
    134     * <p>This factory allows the pair to be created using inference to
    135     * obtain the generic types.</p>
    136     *
    137     * @param <L> the left element type
    138     * @param <R> the right element type
    139     * @param left  the left element, may not be null
    140     * @param right  the right element, may not  be null
    141     * @return a pair formed from the two parameters, not null
    142     * @throws NullPointerException if any input is null
    143     * @since 3.13.0
    144     */
    145    public static <L, R> ImmutablePair<L, R> ofNonNull(final L left, final R right) {
    146        return of(Objects.requireNonNull(left, "left"), Objects.requireNonNull(right, "right"));
    147    }
    148
    149    /**
    150     * Creates an immutable pair of two objects inferring the generic types.
    151     *
    152     * <p>This factory allows the pair to be created using inference to
    153     * obtain the generic types.</p>
    154     *
    155     * @param <L> the left element type
    156     * @param <R> the right element type
    157     * @param right  the right element, may be null
    158     * @return a pair formed from the two parameters, not null
    159     * @since 3.11
    160     */
    161    public static <L, R> Pair<L, R> right(final R right) {
    162        return of(null, right);
    163    }
    164
    165    /** Left object */
    166    public final L left;
    167
    168    /** Right object */
    169    public final R right;
    170
    171    /**
    172     * Create a new pair instance.
    173     *
    174     * @param left  the left value, may be null
    175     * @param right  the right value, may be null
    176     */
    177    public ImmutablePair(final L left, final R right) {
    178        this.left = left;
    179        this.right = right;
    180    }
    181
    182    /**
    183     * {@inheritDoc}
    184     */
    185    @Override
    186    public L getLeft() {
    187        return left;
    188    }
    189
    190    /**
    191     * {@inheritDoc}
    192     */
    193    @Override
    194    public R getRight() {
    195        return right;
    196    }
    197
    198    /**
    199     * Throws {@link UnsupportedOperationException}.
    200     *
    201     * <p>This pair is immutable, so this operation is not supported.</p>
    202     *
    203     * @param value  the value to set
    204     * @return never
    205     * @throws UnsupportedOperationException as this operation is not supported
    206     */
    207    @Override
    208    public R setValue(final R value) {
    209        throw new UnsupportedOperationException();
    210    }
    211
    212}