Transformer分析

/*   *  Licensed to the Apache Software Foundation (ASF) under one or more   *  contributor license agreements.  See the NOTICE file distributed with   *  this work for additional information regarding copyright ownership.   *  The ASF licenses this file to You under the Apache License, Version 2.0   *  (the "License"); you may not use this file except in compliance with   *  the License.  You may obtain a copy of the License at   *   *      http://www.apache.org/licenses/LICENSE-2.0   *   *  Unless required by applicable law or agreed to in writing, software   *  distributed under the License is distributed on an "AS IS" BASIS,   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   *  See the License for the specific language governing permissions and   *  limitations under the License.   */  package org.apache.commons.collections;    /**   * Defines a functor interface implemented by classes that transform one   * object into another.   * <p>   * A Transformer converts the input object to the output object.   * The input object should be left unchanged.   * Transformers are typically used for type conversions, or extracting data   * from an object.   * 
   * Standard implementations of common transformers are provided by   * {@link TransformerUtils}. These include method invokation, returning a constant,   * cloning and returning the string value.   *    * @since Commons Collections 1.0   * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $   *    * @author James Strachan   * @author Stephen Colebourne   */  public interface Transformer {        /**       * Transforms the input object (leaving it unchanged) into some output object.       *       * @param input  the object to be transformed, should be left unchanged       * @return a transformed object       * @throws ClassCastException (runtime) if the input is the wrong class       * @throws IllegalArgumentException (runtime) if the input is invalid       * @throws FunctorException (runtime) if the transform cannot be completed       */      public Object transform(Object input);    }