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;
018    
019    /**
020     * Defines a functor interface implemented by classes that transform one
021     * object into another.
022     * <p>
023     * A <code>Transformer</code> converts the input object to the output object.
024     * The input object should be left unchanged.
025     * Transformers are typically used for type conversions, or extracting data
026     * from an object.
027     * <p>
028     * Standard implementations of common transformers are provided by
029     * {@link TransformerUtils}. These include method invokation, returning a constant,
030     * cloning and returning the string value.
031     * 
032     * @since Commons Collections 1.0
033     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
034     * 
035     * @author James Strachan
036     * @author Stephen Colebourne
037     */
038    public interface Transformer {
039    
040        /**
041         * Transforms the input object (leaving it unchanged) into some output object.
042         *
043         * @param input  the object to be transformed, should be left unchanged
044         * @return a transformed object
045         * @throws ClassCastException (runtime) if the input is the wrong class
046         * @throws IllegalArgumentException (runtime) if the input is invalid
047         * @throws FunctorException (runtime) if the transform cannot be completed
048         */
049        public Object transform(Object input);
050    
051    }