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.BinaryPredicate;
022    import org.apache.commons.functor.UnaryPredicate;
023    
024    /**
025     * Adapts a
026     * {@link BinaryPredicate BinaryPredicate}
027     * to the
028     * {@link UnaryPredicate UnaryPredicate} interface
029     * using a constant left-side 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     * @param <A> the argument type.
039     * @version $Revision: 1157623 $ $Date: 2011-08-14 21:59:51 +0200 (Sun, 14 Aug 2011) $
040     * @author Rodney Waldhoff
041     */
042    public final class LeftBoundPredicate<A> implements UnaryPredicate<A>, Serializable {
043    
044        /**
045         * serialVersionUID declaration.
046         */
047        private static final long serialVersionUID = 3851481216909573294L;
048        /** The {@link BinaryPredicate BinaryPredicate} I'm wrapping. */
049        private final BinaryPredicate<Object, ? super A> predicate;
050        /** The parameter to pass to {@code predicate}. */
051        private final Object param;
052    
053        /**
054         * Create a new LeftBoundPredicate.
055         * @param <L> the left argument type.
056         * @param predicate the predicate to adapt
057         * @param arg the constant argument to use
058         */
059        @SuppressWarnings("unchecked")
060        public <L> LeftBoundPredicate(BinaryPredicate<? super L, ? super A> predicate, L arg) {
061            if (predicate == null) {
062                throw new IllegalArgumentException("BinaryPredicate argument was null");
063            }
064            this.predicate = (BinaryPredicate<Object, ? super A>) predicate;
065            this.param = arg;
066        }
067    
068        /**
069         * {@inheritDoc}
070         */
071        public boolean test(A obj) {
072            return predicate.test(param, obj);
073        }
074    
075        /**
076         * {@inheritDoc}
077         */
078        public boolean equals(Object that) {
079            return that == this || (that instanceof LeftBoundPredicate<?> && equals((LeftBoundPredicate<?>) that));
080        }
081    
082        /**
083         * Learn whether another LeftBoundPredicate is equal to this.
084         * @param that LeftBoundPredicate to test
085         * @return boolean
086         */
087        public boolean equals(LeftBoundPredicate<?> that) {
088            return null != that
089                    && (null == predicate ? null == that.predicate : predicate.equals(that.predicate))
090                    && (null == param ? null == that.param : param.equals(that.param));
091        }
092    
093        /**
094         * {@inheritDoc}
095         */
096        public int hashCode() {
097            int hash = "LeftBoundPredicate".hashCode();
098            if (null != predicate) {
099                hash <<= 2;
100                hash ^= predicate.hashCode();
101            }
102            if (null != param) {
103                hash <<= 2;
104                hash ^= param.hashCode();
105            }
106            return hash;
107        }
108    
109        /**
110         * {@inheritDoc}
111         */
112        public String toString() {
113            return "LeftBoundPredicate<" + predicate + "(" + param + ",?)>";
114        }
115    
116        /**
117         * Adapt a BinaryPredicate to the UnaryPredicate interface.
118         * @param <L> the left argument type.
119         * @param <R> the right argument type.
120         * @param predicate to adapt
121         * @param arg Object argument to always send as the left operand to the wrapped function
122         * @return LeftBoundPredicate
123         */
124        public static <L, R> LeftBoundPredicate<R> bind(BinaryPredicate<? super L, ? super R> predicate, L arg) {
125            return null == predicate ? null : new LeftBoundPredicate<R>(predicate, arg);
126        }
127    }