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.adapter;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.functor.Function;
22 import org.apache.commons.functor.Predicate;
23
24 /**
25 * Adapts a
26 * {@link Predicate Predicate}
27 * to the
28 * {@link Function Function} interface.
29 * <p/>
30 * Note that although this class implements
31 * {@link Serializable}, a given instance will
32 * only be truly <code>Serializable</code> if the
33 * underlying predicate is. Attempts to serialize
34 * an instance whose delegate is not
35 * <code>Serializable</code> will result in an exception.
36 *
37 * @version $Revision: 1156320 $ $Date: 2011-08-10 21:14:50 +0200 (Wed, 10 Aug 2011) $
38 * @author Rodney Waldhoff
39 */
40 public final class PredicateFunction implements Function<Boolean>, Serializable {
41 /**
42 * serialVersionUID declaration.
43 */
44 private static final long serialVersionUID = -8858981355549412629L;
45 /** The {@link Predicate Predicate} I'm wrapping. */
46 private final Predicate predicate;
47
48 /**
49 * Create a new PredicateFunction.
50 * @param predicate to adapt
51 */
52 public PredicateFunction(Predicate predicate) {
53 if (predicate == null) {
54 throw new IllegalArgumentException("Predicate argument was null");
55 }
56 this.predicate = predicate;
57 }
58
59 /**
60 * {@inheritDoc}
61 * Returns <code>Boolean.TRUE</code> (<code>Boolean.FALSE</code>)
62 * when the {@link Predicate#test test} method of my underlying
63 * predicate returns <code>true</code> (<code>false</code>).
64 *
65 * @return a non-<code>null</code> <code>Boolean</code> instance
66 */
67 public Boolean evaluate() {
68 return predicate.test();
69 }
70
71 /**
72 * {@inheritDoc}
73 */
74 public boolean equals(Object that) {
75 return that == this || (that instanceof PredicateFunction && equals((PredicateFunction) that));
76 }
77
78 /**
79 * Learn whether another PredicateFunction is equal to this.
80 * @param that PredicateFunction to test
81 * @return boolean
82 */
83 public boolean equals(PredicateFunction that) {
84 return null != that && (null == predicate ? null == that.predicate : predicate.equals(that.predicate));
85 }
86
87 /**
88 * {@inheritDoc}
89 */
90 public int hashCode() {
91 int hash = "PredicateFunction".hashCode();
92 if (null != predicate) {
93 hash ^= predicate.hashCode();
94 }
95 return hash;
96 }
97
98 /**
99 * {@inheritDoc}
100 */
101 public String toString() {
102 return "PredicateFunction<" + predicate + ">";
103 }
104
105 /**
106 * Adapt a Predicate to the Function interface.
107 * @param predicate to adapt
108 * @return PredicateFunction
109 */
110 public static PredicateFunction adapt(Predicate predicate) {
111 return null == predicate ? null : new PredicateFunction(predicate);
112 }
113
114 }