    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
    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. The class is also {@code final}, so a subclass
    028 * can not add undesirable behavior.</p>
    029 *
    030 * <p>#ThreadSafe# if both paired objects are thread-safe</p>
    031 *
    032 * @param <L> the left element type
    033 * @param <R> the right element type
    034 *
    035 * @since 3.0
    036 */
    037public class ImmutablePair<L, R> extends Pair<L, R> {
    038
    039    /**
    040     * An empty array.
    041     * <p>
    042     * Consider using {@link #emptyArray()} to avoid generics warnings.
    043     * </p>
    044     *
    045     * @since 3.10.
    046     */
    047    public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = {};
    048
    049    /**
    050     * An immutable pair of nulls.
    051     */
    052    // This is not defined with generics to avoid warnings in call sites.
    053    @SuppressWarnings("rawtypes")
    054    private static final ImmutablePair NULL = new ImmutablePair<>(null, null);
    055
    056    /** Serialization version */
    057    private static final long serialVersionUID = 4954918890077093841L;
    058
    059    /**
    060     * Returns the empty array singleton that can be assigned without compiler warning.
    061     *
    062     * @param <L> the left element type
    063     * @param <R> the right element type
    064     * @return the empty array singleton that can be assigned without compiler warning.
    065     *
    066     * @since 3.10.
    067     */
    068    @SuppressWarnings("unchecked")
    069    public static <L, R> ImmutablePair<L, R>[] emptyArray() {
    070        return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
    071    }
    072
    073    /**
    074     * Creates an immutable pair of two objects inferring the generic types.
    075     *
    076     * <p>This factory allows the pair to be created using inference to
    077     * obtain the generic types.</p>
    078     *
    079     * @param <L> the left element type
    080     * @param <R> the right element type
    081     * @param left  the left element, may be null
    082     * @return a pair formed from the two parameters, not null
    083     * @since 3.11
    084     */
    085    public static <L, R> Pair<L, R> left(final L left) {
    086        return ImmutablePair.of(left, null);
    087    }
    088
    089    /**
    090     * Returns an immutable pair of nulls.
    091     *
    092     * @param <L> the left element of this pair. Value is {@code null}.
    093     * @param <R> the right element of this pair. Value is {@code null}.
    094     * @return an immutable pair of nulls.
    095     * @since 3.6
    096     */
    097    @SuppressWarnings("unchecked")
    098    public static <L, R> ImmutablePair<L, R> nullPair() {
    099        return NULL;
    100    }
    101
    102    /**
    103     * Creates an immutable pair of two objects inferring the generic types.
    104     *
    105     * <p>This factory allows the pair to be created using inference to
    106     * obtain the generic types.</p>
    107     *
    108     * @param <L> the left element type
    109     * @param <R> the right element type
    110     * @param left  the left element, may be null
    111     * @param right  the right element, may be null
    112     * @return a pair formed from the two parameters, not null
    113     */
    114    public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
    115        return left != null || right != null ? new ImmutablePair<>(left, right) : nullPair();
    116    }
    117
    118    /**
    119     * Creates an immutable pair from a map entry.
    120     *
    121     * <p>This factory allows the pair to be created using inference to
    122     * obtain the generic types.</p>
    123     *
    124     * @param <L> the left element type
    125     * @param <R> the right element type
    126     * @param pair the existing map entry.
    127     * @return a pair formed from the map entry
    128     * @since 3.10
    129     */
    130    public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
    131        return pair != null ? new ImmutablePair<>(pair.getKey(), pair.getValue()) : nullPair();
    132    }
    133
    134    /**
    135     * Creates an immutable pair of two non-null objects inferring the generic types.
    136     *
    137     * <p>This factory allows the pair to be created using inference to
    138     * obtain the generic types.</p>
    139     *
    140     * @param <L> the left element type
    141     * @param <R> the right element type
    142     * @param left  the left element, may not be null
    143     * @param right  the right element, may not  be null
    144     * @return a pair formed from the two parameters, not null
    145     * @throws NullPointerException if any input is null
    146     * @since 3.13.0
    147     */
    148    public static <L, R> ImmutablePair<L, R> ofNonNull(final L left, final R right) {
    149        return of(Objects.requireNonNull(left, "left"), Objects.requireNonNull(right, "right"));
    150    }
    151
    152    /**
    153     * Creates an immutable pair of two objects inferring the generic types.
    154     *
    155     * <p>This factory allows the pair to be created using inference to
    156     * obtain the generic types.</p>
    157     *
    158     * @param <L> the left element type
    159     * @param <R> the right element type
    160     * @param right  the right element, may be null
    161     * @return a pair formed from the two parameters, not null
    162     * @since 3.11
    163     */
    164    public static <L, R> Pair<L, R> right(final R right) {
    165        return ImmutablePair.of(null, right);
    166    }
    167
    168    /** Left object */
    169    public final L left;
    170
    171    /** Right object */
    172    public final R right;
    173
    174    /**
    175     * Create a new pair instance.
    176     *
    177     * @param left  the left value, may be null
    178     * @param right  the right value, may be null
    179     */
    180    public ImmutablePair(final L left, final R right) {
    181        this.left = left;
    182        this.right = right;
    183    }
    184
    185    /**
    186     * {@inheritDoc}
    187     */
    188    @Override
    189    public L getLeft() {
    190        return left;
    191    }
    192
    193    /**
    194     * {@inheritDoc}
    195     */
    196    @Override
    197    public R getRight() {
    198        return right;
    199    }
    200
    201    /**
    202     * Throws {@link UnsupportedOperationException}.
    203     *
    204     * <p>This pair is immutable, so this operation is not supported.</p>
    205     *
    206     * @param value  the value to set
    207     * @return never
    208     * @throws UnsupportedOperationException as this operation is not supported
    209     */
    210    @Override
    211    public R setValue(final R value) {
    212        throw new UnsupportedOperationException();
    213    }
    214
    215}