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 * @param <L> the left element type.
74 * @param <R> the right element type.
75 * @param left the left element, may be null.
76 * @return an immutable formed from the two parameters, not null.
77 * @since 3.11
78 */
79 public static <L, R> Pair<L, R> left(final L left) {
80 return of(left, null);
81 }
82
83 /**
84 * Returns an immutable pair of nulls.
85 *
86 * @param <L> the left element of this pair. Value is {@code null}.
87 * @param <R> the right element of this pair. Value is {@code null}.
88 * @return an immutable pair of nulls.
89 * @since 3.6
90 */
91 @SuppressWarnings("unchecked")
92 public static <L, R> ImmutablePair<L, R> nullPair() {
93 return NULL;
94 }
95
96 /**
97 * Creates an immutable pair of two objects inferring the generic types.
98 *
99 * @param <L> the left element type.
100 * @param <R> the right element type.
101 * @param left the left element, may be null.
102 * @param right the right element, may be null.
103 * @return an immutable formed from the two parameters, not null.
104 */
105 public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
106 return left != null || right != null ? new ImmutablePair<>(left, right) : nullPair();
107 }
108
109 /**
110 * Creates an immutable pair from a map entry.
111 *
112 * @param <L> the left element type.
113 * @param <R> the right element type.
114 * @param pair the existing map entry.
115 * @return an immutable formed from the map entry.
116 * @since 3.10
117 */
118 public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
119 return pair != null ? new ImmutablePair<>(pair.getKey(), pair.getValue()) : nullPair();
120 }
121
122 /**
123 * Creates an immutable pair of two non-null objects inferring the generic types.
124 *
125 * @param <L> the left element type.
126 * @param <R> the right element type.
127 * @param left the left element, may not be null.
128 * @param right the right element, may not be null.
129 * @return an immutable formed from the two parameters, not null.
130 * @throws NullPointerException if any input is null.
131 * @since 3.13.0
132 */
133 public static <L, R> ImmutablePair<L, R> ofNonNull(final L left, final R right) {
134 return of(Objects.requireNonNull(left, "left"), Objects.requireNonNull(right, "right"));
135 }
136
137 /**
138 * Creates an immutable pair of two objects inferring the generic types.
139 *
140 * @param <L> the left element type.
141 * @param <R> the right element type.
142 * @param right the right element, may be null.
143 * @return an immutable formed from the two parameters, not null.
144 * @since 3.11
145 */
146 public static <L, R> Pair<L, R> right(final R right) {
147 return of(null, right);
148 }
149
150 /** Left object */
151 public final L left;
152
153 /** Right object */
154 public final R right;
155
156 /**
157 * Create a new pair instance.
158 *
159 * @param left the left value, may be null
160 * @param right the right value, may be null
161 */
162 public ImmutablePair(final L left, final R right) {
163 this.left = left;
164 this.right = right;
165 }
166
167 /**
168 * {@inheritDoc}
169 */
170 @Override
171 public L getLeft() {
172 return left;
173 }
174
175 /**
176 * {@inheritDoc}
177 */
178 @Override
179 public R getRight() {
180 return right;
181 }
182
183 /**
184 * Throws {@link UnsupportedOperationException}.
185 *
186 * <p>This pair is immutable, so this operation is not supported.</p>
187 *
188 * @param value the value to set
189 * @return never
190 * @throws UnsupportedOperationException as this operation is not supported
191 */
192 @Override
193 public R setValue(final R value) {
194 throw new UnsupportedOperationException();
195 }
196
197 }