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.composite;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.functor.BinaryPredicate;
22 import org.apache.commons.lang3.Validate;
23
24 /**
25 * Transposes (swaps) the arguments to some other
26 * {@link BinaryPredicate predicate}.
27 * For example, given a predicate <i>p</i>
28 * and the ordered pair of arguments <i>a</i>,
29 * <i>b</i>.
30 * {@link #test tests}
31 * <code>p.test(b,a)</code>.
32 * <p>
33 * Note that although this class implements
34 * {@link Serializable}, a given instance will
35 * only be truly <code>Serializable</code> if the
36 * underlying functor is. Attempts to serialize
37 * an instance whose delegate is not
38 * <code>Serializable</code> will result in an exception.
39 * </p>
40 * @param <L> the left argument type.
41 * @param <R> the right argument type.
42 * @version $Revision: 1365329 $ $Date: 2012-07-24 19:34:23 -0300 (Tue, 24 Jul 2012) $
43 */
44 public class TransposedPredicate<L, R> implements BinaryPredicate<L, R>, Serializable {
45 /**
46 * serialVersionUID declaration.
47 */
48 private static final long serialVersionUID = 3441209087576289240L;
49 // attributes
50 // ------------------------------------------------------------------------
51 /**
52 * The adapted predicate.
53 */
54 private final BinaryPredicate<? super R, ? super L> predicate;
55
56 // constructor
57 // ------------------------------------------------------------------------
58 /**
59 * Create a new TransposedPredicate.
60 * @param predicate the BinaryPredicate to transpose
61 */
62 public TransposedPredicate(BinaryPredicate<? super R, ? super L> predicate) {
63 this.predicate = Validate.notNull(predicate, "BinaryPredicate argument must not be null");
64 }
65
66 // functor interface
67 // ------------------------------------------------------------------------
68 /**
69 * {@inheritDoc}
70 */
71 public final boolean test(L left, R right) {
72 return predicate.test(right, left);
73 }
74
75 /**
76 * {@inheritDoc}
77 */
78 @Override
79 public boolean equals(Object that) {
80 return that == this || (that instanceof TransposedPredicate<?, ?> && equals((TransposedPredicate<?, ?>) that));
81 }
82
83 /**
84 * Learn whether another TransposedPredicate is equal to this.
85 * @param that the TransposedPredicate to test
86 * @return boolean
87 */
88 public boolean equals(TransposedPredicate<?, ?> that) {
89 return null != that && predicate.equals(that.predicate);
90 }
91
92 /**
93 * {@inheritDoc}
94 */
95 @Override
96 public int hashCode() {
97 int hash = "TransposedPredicate".hashCode();
98 hash ^= predicate.hashCode();
99 return hash;
100 }
101
102 /**
103 * {@inheritDoc}
104 */
105 @Override
106 public String toString() {
107 return "TransposedPredicate<" + predicate + ">";
108 }
109
110 // static
111 // ------------------------------------------------------------------------
112 /**
113 * Return the transposition of <code>p</code>.
114 *
115 * @param <L> the left argument type.
116 * @param <R> the right argument type.
117 * @param p BinaryPredicate to transpose
118 * @return TransposedPredicate
119 */
120 public static <L, R> TransposedPredicate<R, L> transpose(BinaryPredicate<? super L, ? super R> p) {
121 return null == p ? null : new TransposedPredicate<R, L>(p);
122 }
123
124 }