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 * http://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 *
34 * @since 3.0
35 */
36 public class ImmutablePair<L, R> extends Pair<L, R> {
37
38 /**
39 * An empty array.
40 * <p>
41 * Consider using {@link #emptyArray()} to avoid generics warnings.
42 * </p>
43 *
44 * @since 3.10.
45 */
46 public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = {};
47
48 /**
49 * An immutable pair of nulls.
50 */
51 // This is not defined with generics to avoid warnings in call sites.
52 @SuppressWarnings("rawtypes")
53 private static final ImmutablePair NULL = new ImmutablePair<>(null, null);
54
55 /** Serialization version */
56 private static final long serialVersionUID = 4954918890077093841L;
57
58 /**
59 * Returns the empty array singleton that can be assigned without compiler warning.
60 *
61 * @param <L> the left element type
62 * @param <R> the right element type
63 * @return the empty array singleton that can be assigned without compiler warning.
64 *
65 * @since 3.10.
66 */
67 @SuppressWarnings("unchecked")
68 public static <L, R> ImmutablePair<L, R>[] emptyArray() {
69 return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
70 }
71
72 /**
73 * Creates an immutable pair of two objects inferring the generic types.
74 *
75 * <p>This factory allows the pair to be created using inference to
76 * obtain the generic types.</p>
77 *
78 * @param <L> the left element type
79 * @param <R> the right element type
80 * @param left the left element, may be null
81 * @return a pair formed from the two parameters, not null
82 * @since 3.11
83 */
84 public static <L, R> Pair<L, R> left(final L left) {
85 return ImmutablePair.of(left, null);
86 }
87
88 /**
89 * Returns an immutable pair of nulls.
90 *
91 * @param <L> the left element of this pair. Value is {@code null}.
92 * @param <R> the right element of this pair. Value is {@code null}.
93 * @return an immutable pair of nulls.
94 * @since 3.6
95 */
96 @SuppressWarnings("unchecked")
97 public static <L, R> ImmutablePair<L, R> nullPair() {
98 return NULL;
99 }
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 }