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.collections.functors;
018    
019    import java.io.Serializable;
020    
021    import org.apache.commons.collections.Predicate;
022    import org.apache.commons.collections.Transformer;
023    
024    /**
025     * Transformer implementation that calls a Predicate using the input object
026     * and then returns the input.
027     * 
028     * @since Commons Collections 3.0
029     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
030     *
031     * @author Stephen Colebourne
032     */
033    public class PredicateTransformer implements Transformer, Serializable {
034    
035        /** Serial version UID */
036        private static final long serialVersionUID = 5278818408044349346L;
037    
038        /** The closure to wrap */
039        private final Predicate iPredicate;
040    
041        /**
042         * Factory method that performs validation.
043         * 
044         * @param predicate  the predicate to call, not null
045         * @return the <code>predicate</code> transformer
046         * @throws IllegalArgumentException if the predicate is null
047         */
048        public static Transformer getInstance(Predicate predicate) {
049            if (predicate == null) {
050                throw new IllegalArgumentException("Predicate must not be null");
051            }
052            return new PredicateTransformer(predicate);
053        }
054    
055        /**
056         * Constructor that performs no validation.
057         * Use <code>getInstance</code> if you want that.
058         * 
059         * @param predicate  the predicate to call, not null
060         */
061        public PredicateTransformer(Predicate predicate) {
062            super();
063            iPredicate = predicate;
064        }
065    
066        /**
067         * Transforms the input to result by calling a predicate.
068         * 
069         * @param input  the input object to transform
070         * @return the transformed result
071         */
072        public Object transform(Object input) {
073            return (iPredicate.evaluate(input) ? Boolean.TRUE : Boolean.FALSE);
074        }
075    
076        /**
077         * Gets the predicate.
078         * 
079         * @return the predicate
080         * @since Commons Collections 3.1
081         */
082        public Predicate getPredicate() {
083            return iPredicate;
084        }
085    
086    }