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