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.Predicate;
22 import org.apache.commons.functor.UnaryPredicate;
23
24 /**
25 * Adapts a
26 * {@link UnaryPredicate UnaryPredicate}
27 * to the
28 * {@link Predicate Predicate} interface
29 * using a constant unary argument.
30 * <p/>
31 * Note that although this class implements
32 * {@link Serializable}, a given instance will
33 * only be truly <code>Serializable</code> if the
34 * underlying objects are. Attempts to serialize
35 * an instance whose delegates are not
36 * <code>Serializable</code> will result in an exception.
37 *
38 * @version $Revision: 1156320 $ $Date: 2011-08-10 21:14:50 +0200 (Wed, 10 Aug 2011) $
39 * @author Rodney Waldhoff
40 */
41 public final class BoundPredicate implements Predicate, Serializable {
42 /**
43 * serialVersionUID declaration.
44 */
45 private static final long serialVersionUID = -5721164265625291834L;
46 /** The {@link UnaryPredicate UnaryPredicate} I'm wrapping. */
47 private final UnaryPredicate<Object> predicate;
48 /** The parameter to pass to {@code predicate}. */
49 private final Object param;
50
51 /**
52 * Create a new BoundPredicate instance.
53 * @param <A> input type
54 * @param predicate the predicate to adapt
55 * @param arg the constant argument to use
56 */
57 @SuppressWarnings("unchecked")
58 public <A> BoundPredicate(UnaryPredicate<? super A> predicate, A arg) {
59 if (predicate == null) {
60 throw new IllegalArgumentException("UnaryPredicate argument was null");
61 }
62 this.predicate = (UnaryPredicate<Object>) predicate;
63 this.param = arg;
64 }
65
66 /**
67 * {@inheritDoc}
68 */
69 public boolean test() {
70 return predicate.test(param);
71 }
72
73 /**
74 * {@inheritDoc}
75 */
76 public boolean equals(Object that) {
77 return that == this || (that instanceof BoundPredicate && equals((BoundPredicate) that));
78 }
79
80 /**
81 * Learn whether another BoundPredicate is equal to this.
82 * @param that BoundPredicate to test
83 * @return boolean
84 */
85 public boolean equals(BoundPredicate that) {
86 return null != that
87 && (null == predicate ? null == that.predicate : predicate.equals(that.predicate))
88 && (null == param ? null == that.param : param.equals(that.param));
89
90 }
91
92 /**
93 * {@inheritDoc}
94 */
95 public int hashCode() {
96 int hash = "BoundPredicate".hashCode();
97 if (null != predicate) {
98 hash <<= 2;
99 hash ^= predicate.hashCode();
100 }
101 if (null != param) {
102 hash <<= 2;
103 hash ^= param.hashCode();
104 }
105 return hash;
106 }
107
108 /**
109 * {@inheritDoc}
110 */
111 public String toString() {
112 return "BoundPredicate<" + predicate + "(" + param + ")>";
113 }
114
115 /**
116 * Adapt the given, possibly-<code>null</code>,
117 * {@link UnaryPredicate UnaryPredicate} to the
118 * {@link Predicate Predicate} interface by binding
119 * the specified <code>Object</code> as a constant
120 * argument.
121 * When the given <code>UnaryPredicate</code> is <code>null</code>,
122 * returns <code>null</code>.
123 *
124 * @param <A> input type
125 * @param predicate the possibly-<code>null</code>
126 * {@link UnaryPredicate UnaryPredicate} to adapt
127 * @param arg the object to bind as a constant argument
128 * @return a <code>BoundPredicate</code> wrapping the given
129 * {@link UnaryPredicate UnaryPredicate}, or <code>null</code>
130 * if the given <code>UnaryPredicate</code> is <code>null</code>
131 */
132 public static <A> BoundPredicate bind(UnaryPredicate<? super A> predicate, A arg) {
133 return null == predicate ? null : new BoundPredicate(predicate, arg);
134 }
135
136 }