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 */
017package org.apache.commons.functor.adapter;
018
019import java.io.Serializable;
020
021import org.apache.commons.functor.Predicate;
022import org.apache.commons.functor.UnaryPredicate;
023import org.apache.commons.lang3.Validate;
024
025/**
026 * Adapts a
027 * {@link UnaryPredicate UnaryPredicate}
028 * to the
029 * {@link Predicate Predicate} interface
030 * using a constant unary argument.
031 * <p/>
032 * Note that although this class implements
033 * {@link Serializable}, a given instance will
034 * only be truly <code>Serializable</code> if the
035 * underlying objects are.  Attempts to serialize
036 * an instance whose delegates are not
037 * <code>Serializable</code> will result in an exception.
038 *
039 * @version $Revision: 1365377 $ $Date: 2012-07-24 20:59:23 -0400 (Tue, 24 Jul 2012) $
040 */
041public 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        this.predicate =
060            (UnaryPredicate<Object>) Validate.notNull(predicate,
061                "UnaryPredicate argument was null");
062        this.param = arg;
063    }
064
065    /**
066     * {@inheritDoc}
067     */
068    public boolean test() {
069        return predicate.test(param);
070    }
071
072    /**
073     * {@inheritDoc}
074     */
075    @Override
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                && predicate.equals(that.predicate)
088                && (null == param ? null == that.param : param.equals(that.param));
089
090    }
091
092    /**
093     * {@inheritDoc}
094     */
095    @Override
096    public int hashCode() {
097        int hash = "BoundPredicate".hashCode();
098        hash <<= 2;
099        hash ^= predicate.hashCode();
100        if (null != param) {
101            hash <<= 2;
102            hash ^= param.hashCode();
103        }
104        return hash;
105    }
106
107    /**
108     * {@inheritDoc}
109     */
110    @Override
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}