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.BinaryFunction;
22
23 /**
24 * Transposes (swaps) the arguments to some other
25 * {@link BinaryFunction function}.
26 * For example, given a function <i>f</i>
27 * and the ordered pair of arguments <i>a</i>,
28 * <i>b</i>.
29 * {@link #evaluate evaluates} to
30 * <code>f.evaluate(b,a)</code>.
31 * <p>
32 * Note that although this class implements
33 * {@link Serializable}, a given instance will
34 * only be truly <code>Serializable</code> if the
35 * underlying functor is. Attempts to serialize
36 * an instance whose delegate is not
37 * <code>Serializable</code> will result in an exception.
38 * </p>
39 * @version $Revision: 1171154 $ $Date: 2011-09-15 17:58:38 +0200 (Thu, 15 Sep 2011) $
40 * @author Rodney Waldhoff
41 */
42 public class TransposedFunction<L, R, T> implements BinaryFunction<L, R, T>, Serializable {
43 /**
44 * serialVersionUID declaration.
45 */
46 private static final long serialVersionUID = -5824252875453493940L;
47 // attributes
48 // ------------------------------------------------------------------------
49 private final BinaryFunction<? super R, ? super L, ? extends T> function;
50
51 // constructor
52 // ------------------------------------------------------------------------
53 /**
54 * Create a new TransposedFunction.
55 * @param function BinaryFunction to transpose.
56 */
57 public TransposedFunction(BinaryFunction<? super R, ? super L, ? extends T> function) {
58 if (function == null) {
59 throw new IllegalArgumentException("BinaryFunction argument was null");
60 }
61 this.function = function;
62 }
63
64 // functor interface
65 // ------------------------------------------------------------------------
66 /**
67 * {@inheritDoc}
68 */
69 public final T evaluate(L left, R right) {
70 return function.evaluate(right, left);
71 }
72
73 /**
74 * {@inheritDoc}
75 */
76 public final boolean equals(Object that) {
77 return that == this || (that instanceof TransposedFunction<?, ?, ?>
78 && equals((TransposedFunction<?, ?, ?>) that));
79 }
80
81 /**
82 * Learn whether another TransposedFunction is equal to this.
83 * @param that TransposedFunction to test
84 * @return boolean
85 */
86 public final boolean equals(TransposedFunction<?, ?, ?> that) {
87 return null != that && (null == function ? null == that.function : function.equals(that.function));
88 }
89
90 /**
91 * {@inheritDoc}
92 */
93 public int hashCode() {
94 int hash = "TransposedFunction".hashCode();
95 if (null != function) {
96 hash ^= function.hashCode();
97 }
98 return hash;
99 }
100
101 /**
102 * {@inheritDoc}
103 */
104 public String toString() {
105 return "TransposedFunction<" + function + ">";
106 }
107
108 // static
109 // ------------------------------------------------------------------------
110 /**
111 * Transpose a BinaryFunction.
112 * @param f BinaryFunction to transpose
113 * @return TransposedFunction
114 */
115 public static <L, R, T> TransposedFunction<R, L, T> transpose(BinaryFunction<? super L, ? super R, ? extends T> f) {
116 return null == f ? null : new TransposedFunction<R, L, T>(f);
117 }
118
119 }