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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  
22  import org.apache.commons.lang3.ObjectUtils;
23  import org.apache.commons.lang3.builder.CompareToBuilder;
24  
25  /**
26   * <p>A pair consisting of two elements.</p>
27   * 
28   * <p>This class is an abstract implementation defining the basic API.
29   * It refers to the elements as 'left' and 'right'. It also implements the
30   * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
31   * 
32   * <p>Subclass implementations may be mutable or immutable.
33   * However, there is no restriction on the type of the stored objects that may be stored.
34   * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
35   *
36   * @param <L> the left element type
37   * @param <R> the right element type
38   *
39   * @since Lang 3.0
40   * @version $Id: Pair.java 1557584 2014-01-12 18:26:49Z britter $
41   */
42  public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
43  
44      /** Serialization version */
45      private static final long serialVersionUID = 4954918890077093841L;
46  
47      /**
48       * <p>Obtains an immutable pair of from two objects inferring the generic types.</p>
49       * 
50       * <p>This factory allows the pair to be created using inference to
51       * obtain the generic types.</p>
52       * 
53       * @param <L> the left element type
54       * @param <R> the right element type
55       * @param left  the left element, may be null
56       * @param right  the right element, may be null
57       * @return a pair formed from the two parameters, not null
58       */
59      public static <L, R> Pair<L, R> of(final L left, final R right) {
60          return new ImmutablePair<L, R>(left, right);
61      }
62  
63      //-----------------------------------------------------------------------
64      /**
65       * <p>Gets the left element from this pair.</p>
66       * 
67       * <p>When treated as a key-value pair, this is the key.</p>
68       * 
69       * @return the left element, may be null
70       */
71      public abstract L getLeft();
72  
73      /**
74       * <p>Gets the right element from this pair.</p>
75       * 
76       * <p>When treated as a key-value pair, this is the value.</p>
77       * 
78       * @return the right element, may be null
79       */
80      public abstract R getRight();
81  
82      /**
83       * <p>Gets the key from this pair.</p>
84       * 
85       * <p>This method implements the {@code Map.Entry} interface returning the
86       * left element as the key.</p>
87       * 
88       * @return the left element as the key, may be null
89       */
90      @Override
91      public final L getKey() {
92          return getLeft();
93      }
94  
95      /**
96       * <p>Gets the value from this pair.</p>
97       * 
98       * <p>This method implements the {@code Map.Entry} interface returning the
99       * right element as the value.</p>
100      * 
101      * @return the right element as the value, may be null
102      */
103     @Override
104     public R getValue() {
105         return getRight();
106     }
107 
108     //-----------------------------------------------------------------------
109     /**
110      * <p>Compares the pair based on the left element followed by the right element.
111      * The types must be {@code Comparable}.</p>
112      * 
113      * @param other  the other pair, not null
114      * @return negative if this is less, zero if equal, positive if greater
115      */
116     @Override
117     public int compareTo(final Pair<L, R> other) {
118       return new CompareToBuilder().append(getLeft(), other.getLeft())
119               .append(getRight(), other.getRight()).toComparison();
120     }
121 
122     /**
123      * <p>Compares this pair to another based on the two elements.</p>
124      * 
125      * @param obj  the object to compare to, null returns false
126      * @return true if the elements of the pair are equal
127      */
128     @SuppressWarnings( "deprecation" ) // ObjectUtils.equals(Object, Object) has been deprecated in 3.2
129     @Override
130     public boolean equals(final Object obj) {
131         if (obj == this) {
132             return true;
133         }
134         if (obj instanceof Map.Entry<?, ?>) {
135             final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
136             return ObjectUtils.equals(getKey(), other.getKey())
137                     && ObjectUtils.equals(getValue(), other.getValue());
138         }
139         return false;
140     }
141 
142     /**
143      * <p>Returns a suitable hash code.
144      * The hash code follows the definition in {@code Map.Entry}.</p>
145      * 
146      * @return the hash code
147      */
148     @Override
149     public int hashCode() {
150         // see Map.Entry API specification
151         return (getKey() == null ? 0 : getKey().hashCode()) ^
152                 (getValue() == null ? 0 : getValue().hashCode());
153     }
154 
155     /**
156      * <p>Returns a String representation of this pair using the format {@code ($left,$right)}.</p>
157      * 
158      * @return a string describing this object, not null
159      */
160     @Override
161     public String toString() {
162         return new StringBuilder().append('(').append(getLeft()).append(',').append(getRight()).append(')').toString();
163     }
164 
165     /**
166      * <p>Formats the receiver using the given format.</p>
167      * 
168      * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
169      * be used to embed the left and right elements. Use {@code %1$s} for the left
170      * element (key) and {@code %2$s} for the right element (value).
171      * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
172      * 
173      * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
174      * @return the formatted string, not null
175      */
176     public String toString(final String format) {
177         return String.format(format, getLeft(), getRight());
178     }
179 
180 }