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: 666186 $ $Date: 2008-06-10 11:34:42 -0500 (Tue, 10 Jun 2008) $
39 * @author Rodney Waldhoff
40 */
41 public final class BoundPredicate implements Predicate, Serializable {
42 /** The {@link UnaryPredicate UnaryPredicate} I'm wrapping. */
43 private UnaryPredicate<Object> predicate;
44 /** The parameter to pass to that predicate. */
45 private Object param;
46
47 /**
48 * Create a new BoundPredicate.
49 * @param predicate the predicate to adapt
50 * @param arg the constant argument to use
51 */
52 @SuppressWarnings("unchecked")
53 public <A> BoundPredicate(UnaryPredicate<? super A> predicate, A arg) {
54 if (predicate == null) {
55 throw new IllegalArgumentException("UnaryPredicate argument was null");
56 }
57 this.predicate = (UnaryPredicate<Object>) predicate;
58 this.param = arg;
59 }
60
61 /**
62 * {@inheritDoc}
63 */
64 public boolean test() {
65 return predicate.test(param);
66 }
67
68 /**
69 * {@inheritDoc}
70 */
71 public boolean equals(Object that) {
72 return that == this || (that instanceof BoundPredicate && equals((BoundPredicate) that));
73 }
74
75 /**
76 * Learn whether another BoundPredicate is equal to this.
77 * @param that BoundPredicate to test
78 * @return boolean
79 */
80 public boolean equals(BoundPredicate that) {
81 return null != that
82 && (null == predicate ? null == that.predicate : predicate.equals(that.predicate))
83 && (null == param ? null == that.param : param.equals(that.param));
84
85 }
86
87 /**
88 * {@inheritDoc}
89 */
90 public int hashCode() {
91 int hash = "BoundPredicate".hashCode();
92 if (null != predicate) {
93 hash <<= 2;
94 hash ^= predicate.hashCode();
95 }
96 if (null != param) {
97 hash <<= 2;
98 hash ^= param.hashCode();
99 }
100 return hash;
101 }
102
103 /**
104 * {@inheritDoc}
105 */
106 public String toString() {
107 return "BoundPredicate<" + predicate + "(" + param + ")>";
108 }
109
110 /**
111 * Adapt the given, possibly-<code>null</code>,
112 * {@link UnaryPredicate UnaryPredicate} to the
113 * {@link Predicate Predicate} interface by binding
114 * the specified <code>Object</code> as a constant
115 * argument.
116 * When the given <code>UnaryPredicate</code> is <code>null</code>,
117 * returns <code>null</code>.
118 *
119 * @param predicate the possibly-<code>null</code>
120 * {@link UnaryPredicate UnaryPredicate} to adapt
121 * @param arg the object to bind as a constant argument
122 * @return a <code>BoundPredicate</code> wrapping the given
123 * {@link UnaryPredicate UnaryPredicate}, or <code>null</code>
124 * if the given <code>UnaryPredicate</code> is <code>null</code>
125 */
126 public static <A> BoundPredicate bind(UnaryPredicate<? super A> predicate, A arg) {
127 return null == predicate ? null : new BoundPredicate(predicate, arg);
128 }
129
130 }