001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.lang3.tuple;
018
019 import java.io.Serializable;
020 import java.util.Map;
021
022 import org.apache.commons.lang3.ObjectUtils;
023 import org.apache.commons.lang3.builder.CompareToBuilder;
024
025 /**
026 * <p>A pair consisting of two elements.</p>
027 *
028 * <p>This class is an abstract implementation defining the basic API.
029 * It refers to the elements as 'left' and 'right'. It also implements the
030 * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
031 *
032 * <p>Subclass implementations may be mutable or immutable.
033 * However, there is no restriction on the type of the stored objects that may be stored.
034 * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
035 *
036 * @param <L> the left element type
037 * @param <R> the right element type
038 *
039 * @since Lang 3.0
040 * @version $Id: Pair.java 1142401 2011-07-03 08:30:12Z bayard $
041 */
042 public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
043
044 /** Serialization version */
045 private static final long serialVersionUID = 4954918890077093841L;
046
047 /**
048 * <p>Obtains an immutable pair of from two objects inferring the generic types.</p>
049 *
050 * <p>This factory allows the pair to be created using inference to
051 * obtain the generic types.</p>
052 *
053 * @param <L> the left element type
054 * @param <R> the right element type
055 * @param left the left element, may be null
056 * @param right the right element, may be null
057 * @return a pair formed from the two parameters, not null
058 */
059 public static <L, R> Pair<L, R> of(L left, R right) {
060 return new ImmutablePair<L, R>(left, right);
061 }
062
063 //-----------------------------------------------------------------------
064 /**
065 * <p>Gets the left element from this pair.</p>
066 *
067 * <p>When treated as a key-value pair, this is the key.</p>
068 *
069 * @return the left element, may be null
070 */
071 public abstract L getLeft();
072
073 /**
074 * <p>Gets the right element from this pair.</p>
075 *
076 * <p>When treated as a key-value pair, this is the value.</p>
077 *
078 * @return the right element, may be null
079 */
080 public abstract R getRight();
081
082 /**
083 * <p>Gets the key from this pair.</p>
084 *
085 * <p>This method implements the {@code Map.Entry} interface returning the
086 * left element as the key.</p>
087 *
088 * @return the left element as the key, may be null
089 */
090 public final L getKey() {
091 return getLeft();
092 }
093
094 /**
095 * <p>Gets the value from this pair.</p>
096 *
097 * <p>This method implements the {@code Map.Entry} interface returning the
098 * right element as the value.</p>
099 *
100 * @return the right element as the value, may be null
101 */
102 public R getValue() {
103 return getRight();
104 }
105
106 //-----------------------------------------------------------------------
107 /**
108 * <p>Compares the pair based on the left element followed by the right element.
109 * The types must be {@code Comparable}.</p>
110 *
111 * @param other the other pair, not null
112 * @return negative if this is less, zero if equal, positive if greater
113 */
114 public int compareTo(Pair<L, R> other) {
115 return new CompareToBuilder().append(getLeft(), other.getLeft())
116 .append(getRight(), other.getRight()).toComparison();
117 }
118
119 /**
120 * <p>Compares this pair to another based on the two elements.</p>
121 *
122 * @param obj the object to compare to, null returns false
123 * @return true if the elements of the pair are equal
124 */
125 @Override
126 public boolean equals(Object obj) {
127 if (obj == this) {
128 return true;
129 }
130 if (obj instanceof Map.Entry<?, ?>) {
131 Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
132 return ObjectUtils.equals(getKey(), other.getKey())
133 && ObjectUtils.equals(getValue(), other.getValue());
134 }
135 return false;
136 }
137
138 /**
139 * <p>Returns a suitable hash code.
140 * The hash code follows the definition in {@code Map.Entry}.</p>
141 *
142 * @return the hash code
143 */
144 @Override
145 public int hashCode() {
146 // see Map.Entry API specification
147 return (getKey() == null ? 0 : getKey().hashCode()) ^
148 (getValue() == null ? 0 : getValue().hashCode());
149 }
150
151 /**
152 * <p>Returns a String representation of this pair using the format {@code ($left,$right)}.</p>
153 *
154 * @return a string describing this object, not null
155 */
156 @Override
157 public String toString() {
158 return new StringBuilder().append('(').append(getLeft()).append(',').append(getRight()).append(')').toString();
159 }
160
161 /**
162 * <p>Formats the receiver using the given format.</p>
163 *
164 * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
165 * be used to embed the left and right elements. Use {@code %1$s} for the left
166 * element (key) and {@code %2$s} for the right element (value).
167 * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
168 *
169 * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
170 * @return the formatted string, not null
171 */
172 public String toString(String format) {
173 return String.format(format, getLeft(), getRight());
174 }
175
176 }