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.math3.util;
018
019 /**
020 * Generic pair.
021 * <br/>
022 * Although the instances of this class are immutable, it is impossible
023 * to ensure that the references passed to the constructor will not be
024 * modified by the caller.
025 *
026 * @param <K> Key type.
027 * @param <V> Value type.
028 *
029 * @since 3.0
030 * @version $Id: Pair.java 1422313 2012-12-15 18:53:41Z psteitz $
031 */
032 public class Pair<K, V> {
033 /** Key. */
034 private final K key;
035 /** Value. */
036 private final V value;
037
038 /**
039 * Create an entry representing a mapping from the specified key to the
040 * specified value.
041 *
042 * @param k Key (first element of the pair).
043 * @param v Value (second element of the pair).
044 */
045 public Pair(K k, V v) {
046 key = k;
047 value = v;
048 }
049
050 /**
051 * Create an entry representing the same mapping as the specified entry.
052 *
053 * @param entry Entry to copy.
054 */
055 public Pair(Pair<? extends K, ? extends V> entry) {
056 this(entry.getKey(), entry.getValue());
057 }
058
059 /**
060 * Get the key.
061 *
062 * @return the key (first element of the pair).
063 */
064 public K getKey() {
065 return key;
066 }
067
068 /**
069 * Get the value.
070 *
071 * @return the value (second element of the pair).
072 */
073 public V getValue() {
074 return value;
075 }
076
077 /**
078 * Get the first element of the pair.
079 *
080 * @return the first element of the pair.
081 * @since 3.1
082 */
083 public K getFirst() {
084 return key;
085 }
086
087 /**
088 * Get the second element of the pair.
089 *
090 * @return the second element of the pair.
091 * @since 3.1
092 */
093 public V getSecond() {
094 return value;
095 }
096
097 /**
098 * Compare the specified object with this entry for equality.
099 *
100 * @param o Object.
101 * @return {@code true} if the given object is also a map entry and
102 * the two entries represent the same mapping.
103 */
104 @Override
105 public boolean equals(Object o) {
106 if (this == o) {
107 return true;
108 }
109 if (!(o instanceof Pair)) {
110 return false;
111 } else {
112 Pair<?, ?> oP = (Pair<?, ?>) o;
113 return (key == null ?
114 oP.key == null :
115 key.equals(oP.key)) &&
116 (value == null ?
117 oP.value == null :
118 value.equals(oP.value));
119 }
120 }
121
122 /**
123 * Compute a hash code.
124 *
125 * @return the hash code value.
126 */
127 @Override
128 public int hashCode() {
129 int result = key == null ? 0 : key.hashCode();
130
131 final int h = value == null ? 0 : value.hashCode();
132 result = 37 * result + h ^ (h >>> 16);
133
134 return result;
135 }
136 }