1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.lang3.tuple;
18
19 import java.util.Map;
20 import java.util.Objects;
21
22 /**
23 * An immutable pair consisting of two {@link Object} elements.
24 *
25 * <p>Although the implementation is immutable, there is no restriction on the objects
26 * that may be stored. If mutable objects are stored in the pair, then the pair
27 * itself effectively becomes mutable.</p>
28 *
29 * <p>#ThreadSafe# if both paired objects are thread-safe</p>
30 *
31 * @param <L> the left element type
32 * @param <R> the right element type
33 * @since 3.0
34 */
35 public class ImmutablePair<L, R> extends Pair<L, R> {
36
37 /**
38 * An empty array.
39 * <p>
40 * Consider using {@link #emptyArray()} to avoid generics warnings.
41 * </p>
42 *
43 * @since 3.10
44 */
45 public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = {};
46
47 /**
48 * An immutable pair of nulls.
49 */
50 // This is not defined with generics to avoid warnings in call sites.
51 @SuppressWarnings("rawtypes")
52 private static final ImmutablePair NULL = new ImmutablePair<>(null, null);
53
54 /** Serialization version */
55 private static final long serialVersionUID = 4954918890077093841L;
56
57 /**
58 * Returns the empty array singleton that can be assigned without compiler warning.
59 *
60 * @param <L> the left element type
61 * @param <R> the right element type
62 * @return the empty array singleton that can be assigned without compiler warning.
63 * @since 3.10
64 */
65 @SuppressWarnings("unchecked")
66 public static <L, R> ImmutablePair<L, R>[] emptyArray() {
67 return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
68 }
69
70 /**
71 * Creates an immutable pair of two objects inferring the generic types.
72 *
73 * <p>This factory allows the pair to be created using inference to
74 * obtain the generic types.</p>
75 *
76 * @param <L> the left element type
77 * @param <R> the right element type
78 * @param left the left element, may be null
79 * @return a pair formed from the two parameters, not null
80 * @since 3.11
81 */
82 public static <L, R> Pair<L, R> left(final L left) {
83 return of(left, null);
84 }
85
86 /**
87 * Returns an immutable pair of nulls.
88 *
89 * @param <L> the left element of this pair. Value is {@code null}.
90 * @param <R> the right element of this pair. Value is {@code null}.
91 * @return an immutable pair of nulls.
92 * @since 3.6
93 */
94 @SuppressWarnings("unchecked")
95 public static <L, R> ImmutablePair<L, R> nullPair() {
96 return NULL;
97 }
98
99 /**
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 }