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}