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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.io.Serializable;
20  import java.util.Map;
21  import java.util.Objects;
22  
23  import org.apache.commons.lang3.builder.CompareToBuilder;
24  import org.apache.commons.lang3.function.FailableBiConsumer;
25  import org.apache.commons.lang3.function.FailableBiFunction;
26  
27  /**
28   * A pair consisting of two elements.
29   *
30   * <p>This class is an abstract implementation defining the basic API.
31   * It refers to the elements as 'left' and 'right'. It also implements the
32   * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
33   *
34   * <p>Subclass implementations may be mutable or immutable.
35   * However, there is no restriction on the type of the stored objects that may be stored.
36   * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
37   *
38   * @param <L> the left element type
39   * @param <R> the right element type
40   *
41   * @since 3.0
42   */
43  public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
44  
45      /** Serialization version */
46      private static final long serialVersionUID = 4954918890077093841L;
47  
48      /**
49       * An empty array.
50       * <p>
51       * Consider using {@link #emptyArray()} to avoid generics warnings.
52       * </p>
53       *
54       * @since 3.10.
55       */
56      public static final Pair<?, ?>[] EMPTY_ARRAY = {};
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> Pair<L, R>[] emptyArray() {
69          return (Pair<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       * @param right  the right element, may be null
82       * @return a pair formed from the two parameters, not null
83       */
84      public static <L, R> Pair<L, R> of(final L left, final R right) {
85          return ImmutablePair.of(left, right);
86      }
87  
88      /**
89       * Creates an immutable pair from a map entry.
90       *
91       * <p>This factory allows the pair to be created using inference to
92       * obtain the generic types.</p>
93       *
94       * @param <L> the left element type
95       * @param <R> the right element type
96       * @param pair the map entry.
97       * @return a pair formed from the map entry
98       * @since 3.10
99       */
100     public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
101         return ImmutablePair.of(pair);
102     }
103 
104     /**
105      * Creates an immutable pair of two non-null objects inferring the generic types.
106      *
107      * <p>This factory allows the pair to be created using inference to
108      * obtain the generic types.</p>
109      *
110      * @param <L> the left element type
111      * @param <R> the right element type
112      * @param left  the left element, may not be null
113      * @param right  the right element, may not  be null
114      * @return a pair formed from the two parameters, not null
115      * @throws NullPointerException if any input is null
116      * @since 3.13.0
117      */
118     public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
119         return ImmutablePair.ofNonNull(left, right);
120     }
121 
122     /**
123      * Accepts this key and value as arguments to the given consumer.
124      *
125      * @param <E> The kind of thrown exception or error.
126      * @param consumer the consumer to call.
127      * @throws E Thrown when the consumer fails.
128      * @since 3.13.0
129      */
130     public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
131         consumer.accept(getKey(), getValue());
132     }
133 
134     /**
135      * Applies this key and value as arguments to the given function.
136      *
137      * @param <V> The function return type.
138      * @param <E> The kind of thrown exception or error.
139      * @param function the consumer to call.
140      * @return the function's return value.
141      * @throws E Thrown when the consumer fails.
142      * @since 3.13.0
143      */
144     public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
145         return function.apply(getKey(), getValue());
146     }
147 
148     /**
149      * Compares the pair based on the left element followed by the right element.
150      * The types must be {@link Comparable}.
151      *
152      * @param other  the other pair, not null
153      * @return negative if this is less, zero if equal, positive if greater
154      */
155     @Override
156     public int compareTo(final Pair<L, R> other) {
157       return new CompareToBuilder().append(getLeft(), other.getLeft())
158               .append(getRight(), other.getRight()).toComparison();
159     }
160 
161     /**
162      * Compares this pair to another based on the two elements.
163      *
164      * @param obj  the object to compare to, null returns false
165      * @return true if the elements of the pair are equal
166      */
167     @Override
168     public boolean equals(final Object obj) {
169         if (obj == this) {
170             return true;
171         }
172         if (obj instanceof Map.Entry<?, ?>) {
173             final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
174             return Objects.equals(getKey(), other.getKey())
175                     && Objects.equals(getValue(), other.getValue());
176         }
177         return false;
178     }
179 
180     /**
181      * Gets the key from this pair.
182      *
183      * <p>This method implements the {@code Map.Entry} interface returning the
184      * left element as the key.</p>
185      *
186      * @return the left element as the key, may be null
187      */
188     @Override
189     public final L getKey() {
190         return getLeft();
191     }
192 
193     /**
194      * Gets the left element from this pair.
195      *
196      * <p>When treated as a key-value pair, this is the key.</p>
197      *
198      * @return the left element, may be null
199      */
200     public abstract L getLeft();
201 
202     /**
203      * Gets the right element from this pair.
204      *
205      * <p>When treated as a key-value pair, this is the value.</p>
206      *
207      * @return the right element, may be null
208      */
209     public abstract R getRight();
210 
211     /**
212      * Gets the value from this pair.
213      *
214      * <p>This method implements the {@code Map.Entry} interface returning the
215      * right element as the value.</p>
216      *
217      * @return the right element as the value, may be null
218      */
219     @Override
220     public R getValue() {
221         return getRight();
222     }
223 
224     /**
225      * Returns a suitable hash code.
226      * The hash code follows the definition in {@code Map.Entry}.
227      *
228      * @return the hash code
229      */
230     @Override
231     public int hashCode() {
232         // see Map.Entry API specification
233         return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
234     }
235 
236     /**
237      * Returns a String representation of this pair using the format {@code ($left,$right)}.
238      *
239      * @return a string describing this object, not null
240      */
241     @Override
242     public String toString() {
243         return "(" + getLeft() + ',' + getRight() + ')';
244     }
245 
246     /**
247      * Formats the receiver using the given format.
248      *
249      * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
250      * be used to embed the left and right elements. Use {@code %1$s} for the left
251      * element (key) and {@code %2$s} for the right element (value).
252      * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
253      *
254      * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
255      * @return the formatted string, not null
256      */
257     public String toString(final String format) {
258         return String.format(format, getLeft(), getRight());
259     }
260 
261 }