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    import java.util.Iterator;
021    import java.util.Map;
022    
023    import org.apache.commons.collections.Predicate;
024    import org.apache.commons.collections.Transformer;
025    
026    /**
027     * Transformer implementation calls the transformer whose predicate returns true,
028     * like a switch statement.
029     * 
030     * @since Commons Collections 3.0
031     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
032     *
033     * @author Stephen Colebourne
034     */
035    public class SwitchTransformer implements Transformer, Serializable {
036    
037        /** Serial version UID */
038        private static final long serialVersionUID = -6404460890903469332L;
039    
040        /** The tests to consider */
041        private final Predicate[] iPredicates;
042        /** The matching transformers to call */
043        private final Transformer[] iTransformers;
044        /** The default transformer to call if no tests match */
045        private final Transformer iDefault;
046    
047        /**
048         * Factory method that performs validation and copies the parameter arrays.
049         * 
050         * @param predicates  array of predicates, cloned, no nulls
051         * @param transformers  matching array of transformers, cloned, no nulls
052         * @param defaultTransformer  the transformer to use if no match, null means return null
053         * @return the <code>chained</code> transformer
054         * @throws IllegalArgumentException if array is null
055         * @throws IllegalArgumentException if any element in the array is null
056         */
057        public static Transformer getInstance(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
058            FunctorUtils.validate(predicates);
059            FunctorUtils.validate(transformers);
060            if (predicates.length != transformers.length) {
061                throw new IllegalArgumentException("The predicate and transformer arrays must be the same size");
062            }
063            if (predicates.length == 0) {
064                return (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
065            }
066            predicates = FunctorUtils.copy(predicates);
067            transformers = FunctorUtils.copy(transformers);
068            return new SwitchTransformer(predicates, transformers, defaultTransformer);
069        }
070    
071        /**
072         * Create a new Transformer that calls one of the transformers depending 
073         * on the predicates. 
074         * <p>
075         * The Map consists of Predicate keys and Transformer values. A transformer 
076         * is called if its matching predicate returns true. Each predicate is evaluated
077         * until one returns true. If no predicates evaluate to true, the default
078         * transformer is called. The default transformer is set in the map with a 
079         * null key. The ordering is that of the iterator() method on the entryset 
080         * collection of the map.
081         * 
082         * @param predicatesAndTransformers  a map of predicates to transformers
083         * @return the <code>switch</code> transformer
084         * @throws IllegalArgumentException if the map is null
085         * @throws IllegalArgumentException if any transformer in the map is null
086         * @throws ClassCastException  if the map elements are of the wrong type
087         */
088        public static Transformer getInstance(Map predicatesAndTransformers) {
089            Transformer[] transformers = null;
090            Predicate[] preds = null;
091            if (predicatesAndTransformers == null) {
092                throw new IllegalArgumentException("The predicate and transformer map must not be null");
093            }
094            if (predicatesAndTransformers.size() == 0) {
095                return ConstantTransformer.NULL_INSTANCE;
096            }
097            // convert to array like this to guarantee iterator() ordering
098            Transformer defaultTransformer = (Transformer) predicatesAndTransformers.remove(null);
099            int size = predicatesAndTransformers.size();
100            if (size == 0) {
101                return (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
102            }
103            transformers = new Transformer[size];
104            preds = new Predicate[size];
105            int i = 0;
106            for (Iterator it = predicatesAndTransformers.entrySet().iterator(); it.hasNext();) {
107                Map.Entry entry = (Map.Entry) it.next();
108                preds[i] = (Predicate) entry.getKey();
109                transformers[i] = (Transformer) entry.getValue();
110                i++;
111            }
112            return new SwitchTransformer(preds, transformers, defaultTransformer);
113        }
114        
115        /**
116         * Constructor that performs no validation.
117         * Use <code>getInstance</code> if you want that.
118         * 
119         * @param predicates  array of predicates, not cloned, no nulls
120         * @param transformers  matching array of transformers, not cloned, no nulls
121         * @param defaultTransformer  the transformer to use if no match, null means return null
122         */
123        public SwitchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
124            super();
125            iPredicates = predicates;
126            iTransformers = transformers;
127            iDefault = (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
128        }
129    
130        /**
131         * Transforms the input to result by calling the transformer whose matching
132         * predicate returns true.
133         * 
134         * @param input  the input object to transform
135         * @return the transformed result
136         */
137        public Object transform(Object input) {
138            for (int i = 0; i < iPredicates.length; i++) {
139                if (iPredicates[i].evaluate(input) == true) {
140                    return iTransformers[i].transform(input);
141                }
142            }
143            return iDefault.transform(input);
144        }
145    
146        /**
147         * Gets the predicates, do not modify the array.
148         * 
149         * @return the predicates
150         * @since Commons Collections 3.1
151         */
152        public Predicate[] getPredicates() {
153            return iPredicates;
154        }
155    
156        /**
157         * Gets the transformers, do not modify the array.
158         * 
159         * @return the transformers
160         * @since Commons Collections 3.1
161         */
162        public Transformer[] getTransformers() {
163            return iTransformers;
164        }
165    
166        /**
167         * Gets the default transformer.
168         * 
169         * @return the default transformer
170         * @since Commons Collections 3.1
171         */
172        public Transformer getDefaultTransformer() {
173            return iDefault;
174        }
175    
176    }