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.functor.core.comparator;
18
19 import java.io.Serializable;
20 import java.util.Comparator;
21
22 import org.apache.commons.functor.BinaryPredicate;
23 import org.apache.commons.functor.UnaryPredicate;
24 import org.apache.commons.functor.adapter.RightBoundPredicate;
25
26 /**
27 * A {@link BinaryPredicate BinaryPredicate} that {@link #test tests}
28 * <code>true</code> iff the left argument is equal to the
29 * right argument under the specified {@link Comparator}.
30 * When no (or a <code>null</code> <code>Comparator</code> is specified,
31 * a {@link Comparable Comparable} <code>Comparator</code> is used.
32 *
33 * @see org.apache.commons.functor.core.IsEqual
34 *
35 * @version $Revision: 1166340 $ $Date: 2011-09-07 21:44:28 +0200 (Wed, 07 Sep 2011) $
36 * @author Rodney Waldhoff
37 *
38 */
39 public final class IsEquivalent<T> implements BinaryPredicate<T, T>, Serializable {
40
41 /**
42 * Basic IsEquivalent instance.
43 */
44 public static final IsEquivalent<Comparable<?>> INSTANCE = IsEquivalent.<Comparable<?>> instance();
45
46 /**
47 * serialVersionUID declaration.
48 */
49 private static final long serialVersionUID = -6392784113015793664L;
50
51 private final Comparator<? super T> comparator;
52
53 /**
54 * Create a new IsEquivalent.
55 */
56 @SuppressWarnings("unchecked")
57 public IsEquivalent() {
58 this(ComparableComparator.INSTANCE);
59 }
60
61 /**
62 * Construct an <code>IsEquivalent</code> {@link BinaryPredicate predicate}
63 * for the given {@link Comparator Comparator}.
64 *
65 * @param comparator the {@link Comparator Comparator}, when <code>null</code>,
66 * a <code>Comparator</code> for {@link Comparable Comparable}s will
67 * be used.
68 */
69 public IsEquivalent(Comparator<? super T> comparator) {
70 if (comparator == null) {
71 throw new IllegalArgumentException("Comparator must not be null");
72 }
73 this.comparator = comparator;
74 }
75
76 /**
77 * Return <code>true</code> iff the <i>left</i> parameter is
78 * equal to the <i>right</i> parameter under my current
79 * {@link Comparator Comparator}.
80 * {@inheritDoc}
81 */
82 public boolean test(T left, T right) {
83 return comparator.compare(left, right) == 0;
84 }
85
86 /**
87 * {@inheritDoc}
88 */
89 public boolean equals(Object that) {
90 return that == this || (that instanceof IsEquivalent<?> && equals((IsEquivalent<?>) that));
91 }
92
93 /**
94 * Learn whether a given IsEquivalent is equal to this.
95 * @param that IsEquivalent to test
96 * @return boolean
97 */
98 public boolean equals(IsEquivalent<?> that) {
99 if (null != that) {
100 if (null == comparator) {
101 return null == that.comparator;
102 }
103 return comparator.equals(that.comparator);
104 }
105 return false;
106 }
107
108 /**
109 * {@inheritDoc}
110 */
111 public int hashCode() {
112 int hash = "IsEquivalent".hashCode();
113 // by construction, comparator is never null
114 hash ^= comparator.hashCode();
115 return hash;
116 }
117
118 /**
119 * {@inheritDoc}
120 */
121 public String toString() {
122 return "IsEquivalent<" + comparator + ">";
123 }
124
125 /**
126 * Get a basic IsEquivalent instance.
127 * @param T
128 * @return IsEquivalent<T>
129 */
130 @SuppressWarnings("unchecked")
131 public static <T extends Comparable<?>> IsEquivalent<T> instance() {
132 return new IsEquivalent<T>(ComparableComparator.INSTANCE);
133 }
134
135 /**
136 * Get an IsEquivalent instance that always compares to <code>arg</code>.
137 * @param right argument
138 * @return UnaryPredicate
139 */
140 public static <T extends Comparable<?>> UnaryPredicate<T> instance(T right) {
141 return RightBoundPredicate.bind(instance(), right);
142 }
143
144 }