001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.functor.adapter;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.functor.Predicate;
022 import org.apache.commons.functor.UnaryPredicate;
023
024 /**
025 * Adapts a
026 * {@link UnaryPredicate UnaryPredicate}
027 * to the
028 * {@link Predicate Predicate} interface
029 * using a constant unary argument.
030 * <p/>
031 * Note that although this class implements
032 * {@link Serializable}, a given instance will
033 * only be truly <code>Serializable</code> if the
034 * underlying objects are. Attempts to serialize
035 * an instance whose delegates are not
036 * <code>Serializable</code> will result in an exception.
037 *
038 * @version $Revision: 1156320 $ $Date: 2011-08-10 21:14:50 +0200 (Wed, 10 Aug 2011) $
039 * @author Rodney Waldhoff
040 */
041 public final class BoundPredicate implements Predicate, Serializable {
042 /**
043 * serialVersionUID declaration.
044 */
045 private static final long serialVersionUID = -5721164265625291834L;
046 /** The {@link UnaryPredicate UnaryPredicate} I'm wrapping. */
047 private final UnaryPredicate<Object> predicate;
048 /** The parameter to pass to {@code predicate}. */
049 private final Object param;
050
051 /**
052 * Create a new BoundPredicate instance.
053 * @param <A> input type
054 * @param predicate the predicate to adapt
055 * @param arg the constant argument to use
056 */
057 @SuppressWarnings("unchecked")
058 public <A> BoundPredicate(UnaryPredicate<? super A> predicate, A arg) {
059 if (predicate == null) {
060 throw new IllegalArgumentException("UnaryPredicate argument was null");
061 }
062 this.predicate = (UnaryPredicate<Object>) predicate;
063 this.param = arg;
064 }
065
066 /**
067 * {@inheritDoc}
068 */
069 public boolean test() {
070 return predicate.test(param);
071 }
072
073 /**
074 * {@inheritDoc}
075 */
076 public boolean equals(Object that) {
077 return that == this || (that instanceof BoundPredicate && equals((BoundPredicate) that));
078 }
079
080 /**
081 * Learn whether another BoundPredicate is equal to this.
082 * @param that BoundPredicate to test
083 * @return boolean
084 */
085 public boolean equals(BoundPredicate that) {
086 return null != that
087 && (null == predicate ? null == that.predicate : predicate.equals(that.predicate))
088 && (null == param ? null == that.param : param.equals(that.param));
089
090 }
091
092 /**
093 * {@inheritDoc}
094 */
095 public int hashCode() {
096 int hash = "BoundPredicate".hashCode();
097 if (null != predicate) {
098 hash <<= 2;
099 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 }