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 1436770 2013-01-22 07:09:45Z ggregory $
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 @Override
129 public boolean equals(final Object obj) {
130 if (obj == this) {
131 return true;
132 }
133 if (obj instanceof Map.Entry<?, ?>) {
134 final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
135 return ObjectUtils.equals(getKey(), other.getKey())
136 && ObjectUtils.equals(getValue(), other.getValue());
137 }
138 return false;
139 }
140
141 /**
142 * <p>Returns a suitable hash code.
143 * The hash code follows the definition in {@code Map.Entry}.</p>
144 *
145 * @return the hash code
146 */
147 @Override
148 public int hashCode() {
149 // see Map.Entry API specification
150 return (getKey() == null ? 0 : getKey().hashCode()) ^
151 (getValue() == null ? 0 : getValue().hashCode());
152 }
153
154 /**
155 * <p>Returns a String representation of this pair using the format {@code ($left,$right)}.</p>
156 *
157 * @return a string describing this object, not null
158 */
159 @Override
160 public String toString() {
161 return new StringBuilder().append('(').append(getLeft()).append(',').append(getRight()).append(')').toString();
162 }
163
164 /**
165 * <p>Formats the receiver using the given format.</p>
166 *
167 * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
168 * be used to embed the left and right elements. Use {@code %1$s} for the left
169 * element (key) and {@code %2$s} for the right element (value).
170 * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
171 *
172 * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
173 * @return the formatted string, not null
174 */
175 public String toString(final String format) {
176 return String.format(format, getLeft(), getRight());
177 }
178
179 }